Patent Application
20110017938
The present invention relates to a half-metallic antiferromagnetic material that has an antiferromagnetic property and exhibits, among electron spin-up and spin-down states, in one electron spin state, a property as a metal and, in the other electron spin state, a property as an insulator or a semiconductor.
A half-metallic antiferromagnetic property is a concept first proposed by van Leuken and de Groot (see Non-Patent Literature 1), and a half-metallic antiferromagnetic material is a substance that exhibits a property as a metal in one electron spin state of electron spin-up and spin-down states and a property as an insulator or a semiconductor in the other electron spin state.
As a half-metallic antiferromagnetic material as described above, various substances have conventionally been proposed. For example, Pickett calculated electronic states of Sr2VCuO6, La2MnVO6 and La2MnCoO6 that have a double perovskite structure, and predicted that, among these intermetallic compounds, La2MnVO6 has a likelihood of exhibiting a half-metallic antiferromagnetic property (see Non-Patent Literature 2).
Furthermore, the present inventors have proposed various antiferromagnetic half-metallic semiconductors having a semiconductor as a host (see Non-Patent Literatures 3 to 7) and have applied for their patents (see Patent Literatures 1 and 2). The antiferromagnetic half-metallic semiconductors that the present inventors have proposed can be obtained by substituting, for example, a group II atom of a group II-VI compound semiconductor or a group III atom of a group III-V compound semiconductor with two or more magnetic ions. Specifically, examples thereof include (ZnCrFe)S, (ZnVCo)S, (ZnCrFe)Se, (ZnVCo)Se, (GaCrNi)N and (GaMnCo)N.
However, as a result of a study conducted by the present inventors, it was found that an intermetallic compound La2MnVO6 predicted by Pickett to be likely to exhibit the half-metallic antiferromagnetic property is low in the likelihood of developing the half-metallic antiferromagnetic property and, even when the half-metallic antiferromagnetic property is developed, it is low in the likelihood of being a stable magnetic structure. Furthermore, in the antiferromagnetic half-metallic semiconductor with a semiconductor as a host, a strong attractive interaction exists between magnetic ions; accordingly, magnetic ions form clusters in the host or two-phase separation is caused in an equilibrium state to result in a state where magnetic ions are precipitated in the host. Accordingly, a problem is that it is difficult to assemble a crystal state and to be chemically stable. Another problem is that owing to weak chemical bond, the magnetic coupling is weak and the magnetic structure is unstable.
In this connection, an object of the present invention is to provide a half-metallic antiferromagnetic material that is chemically stable and has a stable magnetic structure.
A half-metallic antiferromagnetic material according to the present invention is a compound that has a crystal structure of a nickel arsenic type, a zinc blende type, a wurtzite type, a chalcopyrite type or a rock salt type and is constituted of two or more magnetic elements and a chalocogen or a pnictogen, the two or more magnetic elements containing a magnetic element having fewer than 5 effective d electrons and a magnetic element having more than 5 effective d electrons, a total number of effective d electrons of the two or more magnetic elements'being 10 or a value close to 10.
The number of effective d electrons of a magnetic element is a number obtained by subtracting the number of electrons that a chalcogen or a pnictogen loses for covalent bonding or ionic bonding, that is, the number of ionic valency, from the number of all valence electrons of the magnetic element. The number of all valence electrons of a magnetic element is a value-obtained by subtracting the number of core electrons (18 in a 3d transition metal element) from the number of electrons in the atom (atomic number). For example, since a chalcogen is divalent, the numbers of effective d electrons of Cr (atomic number: 24) and Fe (atomic number: 26) are four (=24−18−2) and 6 (=26−18−2), respectively. Furthermore, since the pnictogen is trivalent, the numbers of effective d electrons of Mn (atomic number: 25) and Co (atomic number: 27) are four (=25−18−3) and 6 (=27−18−3), respectively.
Furthermore, the total number of effective d electrons of two or more magnetic elements can be obtained also as shown below. For example, in a half-metallic antiferromagnetic material represented by a composition formula ABX2 (A and B each represent a magnetic element and X represents a chalcogen), the number of valence electrons that the chalcogen X supplies to a bond state owing to sp electrons is 12 (=6×2), and, in a bond state owing to sp electrons, 16 (=8×2) valence electrons per chemical formula weight are accommodated. Accordingly, since four electrons (=16−12) are supplied from magnetic elements A and B to the bond state, a value obtained by subtracting four that is the number of the electrons from the total of the number of all valence electrons of the magnetic element A and the number of all valence electrons of the magnetic element B is the total number of effective d electrons. In the case where the magnetic element A is Cr (atomic number: 24) and the magnetic element B is Fe (atomic number: 26), since the number of all valence electrons of the magnetic element A is 6 (=24−18) and the number of all valence electrons of the magnetic element B is 8 (=26−18), the total number of all valence electrons is 14 and the total number of effective d electrons of the magnetic elements A and B is 10 (=14−4). On the other hand, in a half-metallic antiferromagnetic material where in the composition formula ABX2, X is a pnictogen, since the number of valence electrons that the pnictogen X supplies to a bond state owing to Sp electrons is 10 (=5×2), a value obtained by subtracting a number of the electrons of 6 from the total of the number of all valence electrons of the magnetic element A and the number of all valence electrons of the magnetic element B is the total number of effective d electrons.
Furthermore, also in a half-metallic antiferromagnetic material constituted of three or more magnetic elements and a chalcogen or a pnictogen, for example, a half-metallic antiferromagnetic material represented by a composition formula (ABC)X2 (A, B and C each represent a magnetic element), in a manner similar to a half-metallic antiferromagnetic material constituted of two magnetic elements and a chalcogen or a pnictogen, a total number of effective d electrons can be obtained. Still furthermore, also in a half-metallic antiferromagnetic material where (AC)X2 and (BC)X2 each form a solid solution like (A0.5B0.5C)X2, in a manner similar to the above, a total number of effective d electrons can be obtained. For example, in the case where the magnetic element A represents V, the magnetic element B represents Mn and the magnetic element C represents Fe and X represents a chalcogen, the total number of all valence electrons of the magnetic elements A, B and C is 14 (=5×0.5+7×0.5+8) and the total number of effective d electrons of the magnetic elements A, B and C is 10.
The reason why the compound according to the present invention develops a half-metallic antiferromagnetic property is considered as follows. In the following description, a case where two magnetic elements are contained will be described.
In a nonmagnetic state of a compound represented by a composition formula ABX2 (A and B each represent a magnetic element and X represents a chalcogen or a pnictogen), as shown in
A d orbital of the magnetic element A and a d orbital of the magnetic element B are spin split owing to an interelectronic interaction. At that time, as a magnetic state, a state where a local magnetic moment of the magnetic element A and a local magnetic moment of the magnetic element B are aligned in parallel with each other and a state where a local magnetic moment of the magnetic element A and a local magnetic moment of the magnetic element B are aligned in antiparallel with each other are considered. In addition, a paramagnetic state where local magnetic moments are aligned in arbitrary directions and also other complicated states can be considered. However, it is enough only to study two states where local magnetic moments are aligned in parallel and in antiparallel with each other.
In a state where a local magnetic moment of the magnetic element A and a local magnetic moment of the magnetic element B are aligned in parallel with each other, as shown in
E1=−|t|2/D (Formula 1)
In the above, D represents an energy difference of d orbitals of the magnetic elements A and B and takes a larger value as the difference of the numbers of effective d electrons between the magnetic element A and the magnetic element B becomes larger.
On the other hand, in a state where a local magnetic moment of the magnetic element A and a local magnetic moment of the magnetic element B are aligned in antiparallel with each other, as shown in
While an energy gain due to the superexchange interaction is proportional to a square of the hopping integral t (secondary perturbation), an energy gain due to the double exchange interaction is linearly proportional to the hopping integral t (primary perturbation when degeneration is caused). Accordingly, in general, a larger energy gain is generated by the double exchange interaction than by the superexchange interaction. In order to generate the double exchange interaction, d states have to be degenerated, and, in a state where local magnetic moments are aligned in antiparallel with each other, when a total number of effective d electrons of the magnetic element A and the number of effective d electrons of the magnetic element B is 10 that is the number of maximum occupying electrons of a 3d electron orbital or a value close to 10, such degeneracy is caused.
As mentioned above, when a total number of effective d electrons is 10 or a value close to 10, a case where local magnetic moments of A and B are aligned in antiparallel with each other is advantageous from energy point of view. Furthermore, in a spin-down band that is subjected to an effect of large exchange splitting corresponding to twice the ferromagnetic exchange splitting, as shown in
Furthermore, a zinc blende type crystal structure, a wurtzite type crystal structure and a chalcopyrite type crystal structure, which are strong in covalent property, are 4-coordinated and a nickel arsenic type crystal structure and a rock salt type crystal structure, which have an ionic property, are 6-coordinated, and all crystal structures form a strong chemical bond. However, concerning an s-state or a e-state, a substance having a crystal structure of 4-coordination is smaller in bonding/antibonding splitting to have a semiconductive property, and a substance having a crystal structure of 6-coordination has a more insulative property. A band made of a d-state of the magnetic element comes in a region where a band gap was originally present. Among a spin-up band and a spin-down band, in one spin band, an original band gap remains to develop a half-metallic property. Furthermore, although a d-state of the magnetic element is hybridized with surrounding negative ions, a property of a d-state as an atomic orbital is retained and stable antiferromagnetic property is developed with large magnetic splitting and local magnetic moment remained.
From what was mentioned above, a compound according to the present invention can be said high in the likelihood of developing a half-metallic antiferromagnetic property in a ground state. It is confirmed by a first principle electronic state calculation as will be described below that a half-metallic antiferromagnetic property is developed in a compound according to the present invention.
In addition, in the case where a total number of effective d electrons of two magnetic elements is a value close to 10, since magnitudes of magnetic moments of both magnetic elements are slightly different, it is considered to develop a ferrimagnetic property having a slight magnetic property as a whole. However, in claims and a specification of the present application, “a ferrimagnetic material” is included in “an antiferromagnetic material”.
The half-metallic antiferromagnetic material according to the present invention is not a state where magnetic ions precipitate in a host like a half-metallic antiferromagnetic semiconductor with a semiconductor as a host but a compound obtained by chemically bonding a chalcogen or a pnictogen and a magnetic element together. The bond thereof is sufficiently strong and it can be said a stable compound also from calculation of formation energy. In addition, it is also known that many similar compounds (for example, transition metal chalcogenides having various crystal structures such as nickel arsenic type) exist stably.
Furthermore, since a chemical bond between a magnetic ion and a chalcogen or a pnictogen is strong, also a chemical bond between magnetic ions via a chalcogen or a pnictogen is strong. Here, a magnetic coupling is due to magnetic moment among chemical bond and can be said that the stronger the chemical bond is, the stronger also the magnetic coupling is. Accordingly, the half-metallic antiferromagnetic material according to the present invention can be said strong in the magnetic coupling and stable in a magnetic structure.
A half-metallic antiferromagnetic material having a first specific configuration is constituted of two magnetic elements and a chalcogen, the two magnetic elements being any one combination selected from the groups of Cr and Fe, V and Co, Ti and Ni, Cr and Mn, Cr and Ni, Ti and Co, Cr and Co, V and Fe and V and Ni. Since the chalcogen is divalent, according to the combinations, a total number of effective d electrons takes a value from 9 to 12.
A half-metallic antiferromagnetic material having a second specific configuration is constituted of two magnetic elements and a pnictogen, the two magnetic elements being any one combination selected from the groups of Mn and Co, Cr and Ni, V and Mn and Fe and Ni. Since the pnictogen is trivalent, according to the combinations, a total number of effective d electrons takes a value from 6 to 12.
A half-metallic antiferromagnetic material having a third specific configuration is constituted of three magnetic elements and a chalcogen, the three magnetic elements being any one combination selected from the groups of Co and Ti and Cr, V and Fe and Ni, Fe and Mn and V, Cr and Mn and Co, and Mn and V and Co.
A half-metallic antiferromagnetic material where three magnetic elements are any combination of Co and Ti and Cr, V and Fe and Ni, Fe and Mn and V, and Cr and Mn and Co is represented by, for example, a composition formula (AB0.5C0.5) X2 (A, B and C: magnetic elements, X: chalcogen). In a half-metallic antiferromagnetic material represented by a composition formula (CoTi0.5Cr0.5)X2, since the numbers of effective d electrons of Ti and Cr are 2 and 4, respectively, the number of effective d electrons of Ti0.5Cr0.5 is 3, and since the number of effective d electrons of Co is 7, the total number of effective d electrons of Co and Ti and Cr is 10. Similarly, in all of combinations of V and Fe and Ni, Fe and Mn and V, and Cr and Mn and Co, the total number of effective d electrons is 10.
Furthermore, a half-metallic antiferromagnetic material where three magnetic elements are Mn and V and Co is represented by, for example, a composition formula (Mn0.5V0.5)(CO0.5Mn0.5)X2 (X: chalcogen). Since the numbers of effective d electrons of Mn, V and Co are 5, 3 and 7, respectively, the number of effective d electrons of Mn0.5V0.5 is 4 and the number of effective d electrons of Co0.5 and Mn0.5 is 6, and the total number of effective d electrons is 10.
A half-metallic antiferromagnetic material having a fourth specific configuration is constituted of three magnetic elements and a pnictogen, the three magnetic elements being Co and Fe and Cr.
The half-metallic antiferromagnetic material having the specific configuration is represented by, for example, a composition formula Co(Fe0.5Cr0.5)X2 (X: pnictogen). Since the numbers of effective d electrons of Fe and Cr are 5 and 3, respectively, the number of effective d electrons of Fe0.5Cr0.5 is 4, and since the number of effective d electrons of Co is 6, the total number of effective d electrons is 10.
A half-metallic antiferromagnetic material having a fifth specific configuration is constituted of four magnetic elements and a chalcogen, the four magnetic elements being Ti and Cr and Fe and Ni.
The half-metallic antiferromagnetic material having the specific configuration is represented by, for example, a composition formula (Ti0.5Cr0.5Fe0.5Ni0.5)X2 (X: chalcogen). Since the numbers of effective d electrons of Ti and Cr are 2 and 4, respectively, the number of effective d electrons of Ti0.5Cr0.5 is 3. On the other hand, since the numbers of effective d electrons of Fe and Ni are 6 and 8, respectively, the number of effective d electrons of Fe0.5Ni0.5 is 7. Accordingly, the total number of effective d electrons of Ti and Cr and Ni and Fe is 10.
According to the present invention, a half-metallic antiferromagnetic material that exists chemically stably and has a stable magnetic structure can be realized.
In what follows, an embodiment of the present invention will be specifically described along the drawings.
A half-metallic antiferromagnetic material according to the present invention is an intermetallic compound that has a crystal structure of a nickel arsenic type, a zinc blende type, a wurtzite type, a chalcopyrite type or a rock salt type and is constituted of two or more magnetic elements and a chalocogen or a pnictogen. The two or more magnetic elements contain a magnetic element having fewer than 5 effective d electrons and a magnetic element having more than 5 effective d electrons, and a total number of effective d electrons of the two or more magnetic elements is 10 or a value close to 10. Here, the chalcogen is any element of S, Se, Te and Po. On the other hand, the pnictogen is any element of N, As, Sb and Bi.
Specifically, a half-metallic antiferromagnetic material is constituted of two transition metal elements and a chalcogen and represented by a composition formula ABX2 (A and B: transition metal elements, X: chalcogen). Here, the two transition metal elements are any one combination selected from the groups of Cr and Fe, V and Co, Ti and Ni, Cr and Mn, Cr and Ni, Ti and Co, Cr and Co, V and Fe and V and Ni. Furthermore, a half-metallic antiferromagnetic material can be constituted also of two transition metal elements and a pnictogen and is represented by a composition formula ABX2 (A and B: transition metal elements, X: pnictogen). Here, the two transition metal elements are any one combination selected from the groups of Mn and Co, Cr and Ni, V and Mn and Fe and Ni.
A half-metallic antiferromagnetic material can be constituted also of three transition metal elements and a chalcogen, the three magnetic elements being any one combination selected from the groups of Co and Ti and Cr, V and Fe and Ni, Fe and Mn and V, Cr and Mn and Co, and Mn and V and Co. Furthermore, a half-metallic antiferromagnetic material can also be constituted of three transition metal elements Co, Fe and Cr and a pnictogen. Still furthermore, a half-metallic antiferromagnetic material can be constituted also of four transition metal elements, Ti and Cr and Ni and Fe and a chalcogen.
The half-metallic antiferromagnetic material according to the present invention can be prepared according to a solid state reaction process. In a preparation step, powderized magnetic elements and chalcogen or pnictogen are thoroughly mixed, followed by encapsulating in a quartz glass tube and by heating at 1000° C. or more, further followed by annealing. Furthermore, a half-metallic antiferromagnetic material having a non-equilibrium crystal structure, for example, zinc blende type (CrFe)S2, is crystal grown according to molecular beam epitaxy on a substrate.
The half-metallic antiferromagnetic material according to the present invention is not a state where magnetic ions precipitate in a host like a half-metallic antiferromagnetic semiconductor with a semiconductor as a host but a compound obtained by chemically bonding a chalcogen or a pnictogen and a magnetic, element together. The bond thereof is sufficiently strong and it can also be said a stable compound from calculation of formation energy. In addition, it is also known that many similar compounds (for example, transition metal chalcogenides having various crystal structures such as nickel arsenic type) exist stably.
Furthermore, since a chemical bond between a magnetic ion and a chalcogen or a pnictogen is strong, also a chemical bond between magnetic ions via a chalcogen or a pnictogen is strong. Here, a magnetic coupling is due to magnetic moment among chemical bond and can be said that the stronger the chemical bond is, the stronger also the magnetic coupling is. Accordingly, the half-metallic antiferromagnetic material according to the present invention can be said strong in the magnetic coupling and stable in a magnetic structure.
Furthermore, the half-metallic antiferromagnetic material according to the present invention can be readily prepared as mentioned above.
A half-metallic antiferromagnetic material, being a substance of which Fermi surface is 100% spin split, is useful as a spintronic material. Furthermore, a half-metallic antiferromagnetic material does not have a magnetic property and thereby is stable to external perturbation, does not generate magnetic shape anisotropy and thereby is high in likelihood of readily realizing a spin flip by current or spin injection and is expected to apply in a broader field such as a high performance magnetic memory and a magnetic head material.
For example, an application to an MRAM (Magnetic Random Access Memory) can be considered.
In an antiferromagnetic material, a concept corresponding to a magnetic wall is called an antiferromagnetic domain boundary (domain boundary). In an antiferromagnetic material having a magnetic structure such as shown in
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a chalcopyrite type crystal structure and represented by a composition formula (CrFe)Po2.
In order to confirm that the intermetallic compound of the present Example has a half-metallic antiferromagnetic property, the present inventors conducted a first principle electronic state calculation. Here, as a method of the first principle electronic state calculation, a known KKR-CPA-LDA method obtained by combining a KKR (Korringa-kohn-Rostoker) method (also called a Green function method), a CPA (Coherent-Potential Approximation) method and an LDA (Local-Density Approximation) method was adopted (Monthly publication “Kagaku Kogyo, Vol. 53, No. 4 (2002)” pp. 20-24, and “Shisutemu/Seigyo/Joho, Vol. 48, No. 7” pp. 256-260).
As shown with a solid line in the figure, a state density of spin-down electrons is zero to form a band gap Gp and a Fermi energy exists in the band gap. On the other hand, a state density of spin-up electrons is larger than zero in the vicinity of the Fermi energy. Thus, while a state of spin-down electrons exhibits a property as a semiconductor, a state of spin-up electrons exhibits a property as a metal, that is, it can be said that a half-metallic property is developed.
Furthermore, since Po that is a chalcogen is divalent, the numbers of effective d electrons of Cr and Fe are 4 and 6, respectively, and thereby a total number of effective d electrons is 10. When a total state density of spin-up electrons and a total state density of spin-down electrons were each integrated up to the Fermi energy, both integral values were the same; accordingly, it can be said that magnetic moments of Fe and Cr cancel out each other and thereby magnetization is zero as a whole.
From the results mentioned above, it can be said that the intermetallic compound of the present Example has a half-metallic antiferromagnetic property.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a chalcopyrite type crystal structure and represented by a composition formula (CrFe)S2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a chalcopyrite type crystal structure and represented by a composition formula (CrFe)Se2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a chalcopyrite type crystal structure and represented by a composition formula (CrFe)Te2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a chalcopyrite type crystal structure and represented by a composition formula (VCo)S2.
From a state density curve shown with a solid line in the figure, it can be said that a half-metallic property is developed. Furthermore, since S that is chalcogen is divalent, the numbers of effective d electrons of V and Co are 3 and 7, respectively, a total number of effective d electrons is 10. When a total state density of spin-up electrons and a total state density of spin-down electrons were each integrated up to the Fermi energy, both integral values were the same; accordingly, it can be said that magnetic moments of Co and V cancel out each other and thereby magnetization as a whole is zero.
From the result mentioned above, it can be said that the intermetallic compound of the present Example has a half-metallic antiferromagnetic property.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a chalcopyrite type crystal structure and represented by a composition formula (VCo)Se2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a rock salt type crystal structure and represented by a composition formula (CrFe)S2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a rock salt type crystal structure and represented by a composition formula (VCo)S2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a nickel arsenic type crystal structure and represented by a composition formula (CrFe)Se2.
Furthermore, a magnetic transition temperature (Neel temperature) where an antiferromagnetic state transitions to a paramagnetic state was calculated and found to be 1094K. Here, the Neel temperature was calculated according to a known method that uses Cluster approximation (J. Phys.: Condens. Matter 19 (2007) 365233).
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a wurtzite type crystal structure and represented by a composition formula (CrFe)S2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a wurtzite type crystal structure and represented by a composition formula (CrFe)Se2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (FeCr)S2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (CrFe)Se2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (CrFe)Te2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (MnCr)Te2.
From a state density curve shown with a solid line in the figure, it can be said that a half-metallic property is developed. Furthermore, since Te that is a chalcogen is divalent, the numbers of effective d electrons of Mn and Cr are 5 and 4, respectively, and the total number of effective d electrons is 9. When a total state density of spin-up electrons and a total state density of spin-down electrons were each integrated up to the Fermi energy, both integral values were slightly different; accordingly, it can be said that slight magnetization remains.
From the result mentioned above, it can be said that the intermetallic compound of the present Example has a half-metallic ferrimagnetic property. In addition, when concentrations of Mn and Cr are controlled, an intermetallic compound having an antiferromagnetic property can be obtained.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (TiCo)Te2.
From a state density curve shown with a solid line in the figure, it can be said that a half-metallic property is developed. Furthermore, since Te that is a chalcogen is divalent, the numbers of effective d electrons of Ti and Co are 2 and 7, respectively, and the total number of effective d electrons is 9. When a total state density of spin-up electrons and a total state density of spin-down electrons were each integrated up to the Fermi energy, both integral values were slightly different; accordingly, it can be said that slight magnetization remains.
From the result mentioned above, it can be said that the intermetallic compound of the present Example has a half-metallic ferrimagnetic property. In addition, when concentrations of Ti and Co are controlled, an intermetallic compound having an antiferromagnetic property can be obtained.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (TiNi)Po2.
From a state density curve shown with a solid line in the figure, it can be said that a half-metallic property is developed. Furthermore, since Po that is a chalcogen is divalent, the numbers of effective d electrons of Ti and Ni are 2 and 8, respectively, and the total number of effective d electrons is 10. When a total state density of spin-up electrons and a total state density of spin-down electrons were each integrated up to the Fermi energy, both integral values were the same; accordingly, it can be said that magnetic moments of Ni and Ti cancel out each other and thereby magnetization as a whole is zero.
From the result mentioned above, it can be said that the intermetallic compound of the present Example has a half-metallic antiferromagnetic property.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (TiNi)Se2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (VCo)Po2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (VCo)S2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (VCo)Se2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (VCo)Te2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a nickel arsenic type crystal structure and represented by a composition formula (MnCo)N2.
From a state density curve shown with a solid line in the figure, it can be said that a half-metallic property is developed. Furthermore, since N that is a pnictogen is trivalent, the numbers of effective d electrons of Mn and Co are 4 and 6, respectively, and the total number of effective d electrons is 10. When a total state density of spin-up electrons and a total state density of spin-down electrons were each integrated up to the Fermi energy, both integral values were the same; accordingly, it can be said that magnetic moments of Co and Mn cancel out each other and thereby magnetization as a whole is zero.
From the result mentioned above, it can be said that the intermetallic compound of the present Example has a half-metallic antiferromagnetic property.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (MnCo)N2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (CrNi)N2.
From a state density curve shown with a solid line in the figure, it can be said that a half-metallic property is developed. Furthermore, since N is trivalent, the numbers of effective d electrons of Cr and Ni are 3 and 7, respectively, and the total number of effective d electrons is 10. When a total state density of spin-up electrons and a total state density of spin-down electrons were each integrated up to the Fermi energy, both integral values were the same; accordingly, it can be said that magnetic moments of Ni and Cr cancel out each other and thereby magnetization as a whole is zero.
From the result mentioned above, it can be said that the intermetallic compound of the present Example has a half-metallic antiferromagnetic property.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (FeNi)As2.
From a state density curve shown with a solid line in the figure, it can be said that a half-metallic property is developed. Furthermore, since As that is a pnictogen is trivalent, the numbers of effective d electrons of Fe and Ni are 5 and 7, respectively, and the total number of effective d electrons is 12. When a total state density of spin-up electrons and a total state density of spin-down electrons were each integrated up to the Fermi energy, both integral values were slightly different; accordingly, it can be said that slight magnetization remains.
From the result mentioned above, it can be said that the intermetallic compound of the present Example has a half-metallic ferrimagnetic property.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a wurtzite type crystal structure and represented by a composition formula (MnCo)N2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a rock salt type crystal structure and represented by a composition formula (MnCo)N2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a chalcopyrite type crystal structure and represented by a composition formula (MnCo)N2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a chalcopyrite type crystal structure and represented by a composition formula (CrNi)N2.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (CrMn0.5Co0.5)Se2.
From a state density curve shown with a solid line in the figure, it can be said that a half-metallic property is developed. Furthermore, since Se that is a chalcogen is divalent, the numbers of effective d electrons of Mn and Co are 5 and 7, respectively, and the number of effective d electrons of Mn0.5Co0.5 is 6. Furthermore, since the number of effective d electrons of Cr is 4, the total number of effective d electrons is 10. When a total state density of spin-up electrons and a total state density of spin-down electrons were each integrated up to the Fermi energy, both integral values were the same; accordingly, it can be said that magnetic moments of Cr and Mn and Co cancel out each other and thereby magnetization as a whole is zero.
From the result mentioned above, it can be said that the intermetallic compound of the present Example has a half-metallic antiferromagnetic property.
A half-metallic antiferromagnetic material of the present Example is an intermetallic compound having a zinc blende type crystal structure and represented by a composition formula (Ti0.5Cr0.5Fe0.5Ni0.5)Se2.
From a state density curve shown with a solid line in the figure, it can be said that a half-metallic property is developed. Furthermore, since Se that is a chalcogen is divalent, the numbers of effective d electrons of Ti and Cr are 2 and 4, respectively, and the number of effective d electrons of Ti0.5Cr05 is 3. On the other hand, since the numbers of effective d electrons of Fe and Ni are 6 and 8, respectively, the number of effective d electrons Fe0.5Ni0.5 is 7. Accordingly, the total number of effective d electrons of Ti and Cr and Ni and Fe is 10. When a total state density of spin-up electrons and a total state density of spin-down electrons were each integrated up to the Fermi energy, both integral values were the same; accordingly, it can be said that magnetic moment of Ni and Fe and magnetic moment of Ti and Cr cancel out each other and thereby magnetization as a whole is zero.
From the result mentioned above, it can be said that the intermetallic compound of the present Example has a half-metallic antiferromagnetic property.
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For example, as to CrFeSe2, as mentioned above, since Se that is a chalcogen is divalent, the numbers of effective d electrons of Cr and Fe are 4 and 6, respectively, and the total number of effective d electrons is 10. CrFeSe2 exhibits, as shown in the figures and tables, a half-metallic antiferromagnetic property even in the case where CrFeSe2 has any of crystal structures of a nickel arsenic type, a zinc blende type, a wurtzite type, a rock salt type and a chalcopyrite type.
Furthermore, the Neel temperatures of nickel arsenic type CrFeSe2, zinc blende type CrFeTe2, zinc blende type VCoTe2, zinc blende type CrFeS2, zinc blende type VCoS2, zinc blende type CrFeSe2 and zinc blende type VCoSe2 are 1094K, 640K, 759K, 1016K, 1025K, 926K and 880K, respectively, that is, values far higher than room temperature. The Neel temperature of an antiferromagnetic half-metallic semiconductor is several hundreds K at the highest and several tens k at the lowest, and, according to nickel arsenic type CrFeSe2, zinc blende type CrFeS2, zinc blende type VCoS2 and zinc blende type CrFeSe2, the Neel temperature higher than that of an antiferromagnetic half-metallic semiconductor can be obtained. It is considered that also of intermetallic compounds other than the foregoing seven intermetallic compounds, the Neel temperature exceeding room temperature can be obtained.
As illustrated in the figures and tables, among intermetallic compounds to which the first principle electronic state calculation was conducted, intermetallic compounds exhibiting a ferrimagnetic property are contained. However, it is considered that, when conditions such as a concentration of magnetic elements are controlled, the likelihood of developing antiferromagnetic property is high.
In addition, among the intermetallic compounds illustrated in the figures and tables, nickel arsenic type CrFeSe2, zinc blende type CrFeTe2, zinc blende type VCoTe2, zinc blende type CrFeS2, zinc blende type VCoS2, zinc blende type CrFeSe2, zinc blende type VCoSe2, wurtzite type CrFeS2, wurtzite type CrFeSe2, rock salt type CrFeS2, chalcopyrite type CrFeTe2, chalcopyrite type CrFeS2, chalcopyrite type VCoS2, chalcopyrite type CrFeSe2, chalcopyrite type VCoSe2 and chalcopyrite type CrFePo2 exist energetically very stably, can obtain enough high Neel temperature and are harmless substances; accordingly, these intermetallic compounds are considered very promising as the half-metallic antiferromagnetic material.
Furthermore, the present inventors conducted the first principle electronic state calculation also of zinc blende type Co(Ti0.5Cr0.5)X2, zinc blende type V(Fe0.5Ni0.5)X2, zinc blende type (Ti0.5Cr0.5)(Ni0.5Fe0.5)X2, zinc blende type Fe(Mn0.5V0.5)X2, zinc blende type Cr(Mn0.5Co0.5)X2, zinc blende type (Mn0.5Vo0.5)(Co0.5Mn0.5)X2, nickel arsenic type Co(Ti0.5Cr0.5)X2, nickel arsenic type V(Ni0.5Fe0.5)X2, nickel arsenic type (Ti0.5Cr0.5)(Ni0.5Fe0.5)X2, chalcopyrite type Co (Ti0.5Cr0.5)X2, chalcopyrite type V(Ni0.5Fe0.5)X2, chalcopyrite type (Ti0.5Cr0.5)(Ni0.5Fe0.5)X2, wurtzite type V(Fe0.5Mn0.5)X2, wurtzite type (V0.5Mn0.5)(Mn0.5Co0.5)X2 and rock salt type Co(Ti0.5Cr0.5)X2, all of which contains a chalcogen X (X is Se, Po, Te or S), and confirmed that all intermetallic compounds have a half-metallic antiferromagnetic property. Furthermore, the first principle electronic state calculation was conducted also of zinc blende type Co(Fe0.5Cr0.5)N2 containing a pnictogen and confirmed that it has a half-metallic antiferromagnetic property.
In addition, as combinations between two or more magnetic elements and a chalcogen or a pnictogen, also others than the foregoing combinations to which the first principle electronic state calculation was conducted are considered to have likelihood of developing a half-metallic antiferromagnetic property.
As mentioned above, the half-metallic antiferromagnetic materials according to the present invention have a stable magnetic structure that is chemically stable and has the Neel temperature far higher than room temperature. Accordingly, a device that uses the half-metallic antiferromagnetic material can operate stably at room temperature.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-073917 | Mar 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/055242 | 3/18/2009 | WO | 00 | 9/21/2010 |
