The instant nonprovisional patent application claims priority to Japanese Patent Application No. 2007-323468 filed Dec. 14, 2007 and which is incorporated by reference in its entirety herein for all purposes.
The recording density of a magnetic recording/reproducing apparatus has been increasing at an annual rate from 40 to 60%, and is estimated to reach Tbit/in2 in the near future. Accordingly, it is required that a magnetic recording/reproducing head has higher output and higher resolving power. Presently, the magnetic reproducing heads such as a CPP-GMR (Current Perpendicular to Plane Giant Magneto Resistance) head in which a sense current is passed perpendicularly to the laminated plane, and a TMR (Tunneling Magneto Resistance) head, have been proposed. However, for these heads, it may be difficult to make the gap length Gw between shields 30 nm or less due to the requirements for the film thickness of an element, and difficult to apply them to the medium of 1 Tbit/in2 or more in respect of the resolving power. For example, the gap length of the reproducing head for the medium of 1 Tbit/in2 is Gw=25 nm, which can not be treated by the prior art such as the CPP-GMR or TMR.
Therefore, a high resolving power reproducing head using a spin accumulation effect has been proposed in “Spin Injection and Spin Accumulation in all-metal Mesoscopic Spin Valves”, F. J. Jedema et al., Physical Review B, vol. 67, (2003), p. 85319 (“non-patent document 1”), and Japanese Patent Publication No. 2004-342241 (“patent document 1”). The spin accumulation effect is a phenomenon in which when a current is passed from a ferromagnetic substance to a non-magnetic metal, spin polarized electrons are accumulated in the non-magnetic metal in the range of spin diffusion length λ. The spin diffusion length λ represents the distance where information of spin disappears (spin is reversed) and is a material inherent value.
Herein, a basic element (spin accumulation element) structure in which a non-magnetic metallic fine line is used as the non-magnetic substance and two magnetic substances are laminated on the non-magnetic fine line, will be described below. Of the two magnetic substances, the first magnetic substance is used as a spin injection source by passing a current from the first magnetic substance to the non-magnetic substance. The other or second magnetic substance is a detection part for the output voltage with spin accumulation effect. Since the ferromagnetic substance generally has a different spin density (the number of up spin electrons and the number of down spin electrons are different) at the Fermi level, a difference in the spin density is induced in the non-magnetic fine line by passing a current from the first magnetic substance to the non-magnetic substance. It is well known that due to the accumulated spin polarized electrons, the non-magnetic substance behaves like ferromagnetic substance in the range of spin diffusion length (see non-patent document 1 and “Spin Injection and Detection in Magnetic Nanostructures”, Physics Review B, vol. 67, (2003), p. 52409 “non-patent document 2”). Using this effect, a voltage difference ΔV is produced depending on the magnetization directions of the first magnetic substance and the second magnetic substance. This voltage difference is called an output voltage ΔV of the spin accumulation element. As a method for measuring the output voltage, a non-local voltage measurement in which no current flows through the voltage detection part is generally employed (see non-patent document 1). To increase ΔV, it is effective that the spin diffusion length λ is made longer, or the electrode distance d1 between two electrodes is decreased as disclosed in Japanese Patent Publication No. 2004-186274 (“patent document 2”).
The reproducing head using the basic element has a feature that a fixed layer and a free layer can be fully separated, and the gap length between shields can be narrowed down. However, the conventional spin accumulation element does not have enough output, and is required to have the higher output. One of the methods for increasing the output voltage of the reproducing head using the spin accumulation effect is to narrow down the magnetic substance interval d1 between two magnetic substances making up the spin accumulation element. However, with the present micro fabrication technique, the magnetic substance interval is about 30 nm at minimum, and impossible to narrow down to infinitesimal. Also, if the magnetic substance interval distance is smaller, a magnetic interaction acts between two magnetic substances, possibly degrading the magnetic characteristics. Therefore, there is a demand for a new method for reducing the attenuation of spin electrons without narrowing down the magnetic substance interval.
Embodiments of the present invention provide an accumulation element with high resolving power and high output suitable for magnetic recording and reproducing at high recording density. As shown in the embodiment of
a)-4(c) are cross-sectional views of a fourth spin accumulation element.
a)-7(c) are schematic views of a reproducing head using the first spin accumulation element.
a) and 8(b) are explanatory views of the reversible spin Hall effect.
a), 9(b) and 9(c) are a cross-sectional view, a side view as seen from the spin injection part, and a plan view as seen from the top of the fifth spin accumulation element, respectively.
a)-11(d) are schematic views of the reproducing head using the fifth spin accumulation element.
Embodiments of the present invention relate to a magnetic head having a magneto-resistive effect element and a magnetic recording apparatus using the magnetic head.
The spin accumulation element of embodiments of the invention has a plurality of spin injection parts. Though the spin injection was conventionally performed using the single spin injection part, a plurality of spin injection parts are provided to increase the total amount of spin electrons in the invention.
In embodiments of the invention, as a first spin injection part, a first magnetic conductor, of which the magnetization is fixed in one direction, is formed on a non-magnetic conductor. Also, a second spin injection part is formed on the opposite side of the first spin injection part in the perpendicular direction of the ingredient film, with the non-magnetic conductor sandwiched, or formed on the same side of the first spin injection part and spaced from the first spin injection part on the non-magnetic conductor. The second spin injection part has a second magnetic conductor, of which the direction of magnetization is anti-parallel to that of the first magnetic conductor of the first spin injection part. Also, as a detection part of the output voltage, a third magnetic conductor is formed on the non-magnetic conductor in the range of spin diffusion length from the spin injection part. When a sense current is passed from the first spin injection part to the non-magnetic conductor and to the second spin injection part, spin-polarized electrons are injected from the first and second spin injection parts into the non-magnetic conductor. Thereby, the spin electron density in the non-magnetic conductor is increased, and the output voltage due to the spin accumulation effect is increased.
Also, the second spin injection part may have the non-magnetic conductor, and when a current is passed through the second spin injection part, spin polarized electrons produced due to a reversible spin Hall effect may be injected.
With embodiments of the invention, the amount of spin electrons accumulated in the non-magnetic substance can be increased over the conventional spin accumulation element. As one example, the output signal due to the spin accumulation effect is increased 100% or more over the spin accumulation element using the single spin injection part. This is caused by the effect of the plurality of spin injection parts and the mirror reflection of spin electrons in the non-magnetic conductor. As a result, it is possible to provide the magnetic reproducing head with high resolving power and high output.
Embodiments of the present invention will be described below in detail.
The non-magnetic conductor 1 may be made of a non-magnetic conductive metal such as Cu, Ag, Al, Yb, Ru, Ir or Rh, or a conductive compound containing GaAs, Si, TiN, TiO or ReO3 as the main component. The distance d1 between the first magnetic conductor 3 and the third magnetic conductor 6 is desirably shorter (d1<λ) than a spin diffusion length λ inherent to each substance to produce a full output as a magnetic reproducing head, although the effect is observable under the condition of d1>λ. A barrier layer 2 may be a monolayer or laminated film made of the material containing at least one kind of MgO, Al2O3, AlN, SiO2, HfO2, Zr2O3, Cr2O3, TiO2 and SrTiO3. The magnetic conductor 3 may be made of the material of Co, Ni, Fe or Mn, or alloy or compound containing at least one kind of these elements as the main component. Further, embodiments of the present invention also cover the magnetic layer containing an oxide having a structure of AB2O4 (where A is at least one of Fe, Co and Zn, and B is one of Fe, Co, Ni, Mn and Zn) represented by half metal Fe3O4, a compound in which one or more components of transition metals Fe, Co, Ni, Cr and Mn are added to CrO2, CrAs, CrSb or ZnO, a compound in which Mn is added to GaN, or a whistler alloy of the type C2D×E1×F (where C is at least one kind of Co, Cu and Ni, D and E are one kind of Mn, Fe and Cr, and F is at least one component of Al, Sb, Ge, Si, Ga and Sn) represented by CO2MnGe, CO2MnSb and CO2Cr0.6Fe0.4Al. The antiferromagnetic conductor 4 may be made of MnIr, MnPt or MnRh.
In the first spin accumulation element, when a current Ic is passed from the first spin injection part 10 to the non-magnetic conductor 1, up polarized spin electrons (spin electrons Is1↑) are injected from the first spin injection part into the non-magnetic conductor 1. The injected spin electrons Is1↑, of which the polarization direction is reverse to the magnetization direction of the second magnetic conductor 8, are reflected from the interface with the second spin injection part 11, and efficiently injected into the non-magnetic conductor 1. On the other hand, due to a current passing from the non-magnetic conductor 1 to the second magnetic conductor 8, down spin electrons Is2↓ in the non-magnetic conductor 1 are transmitted into the second spin injection part 11, so that Is2↑ are accumulated in the non-magnetic conductor 1. In other words, Is2↑ are injected, independently of Is1↑, into the non-magnetic conductor 1 by the second spin injection part 11. The injected spin electrons Is2↑ are also reflected from the interface with the first spin injection part 10, as previously described. Thus, spin electrons synthesized of Is1↑ and Is2↑ are accumulated in the non-magnetic conductor 1, and an output voltage dependent on the magnetization direction of the third magnetic conductor 6 occurs between the third magnetic conductor 6 and the non-magnetic conductor 1.
a) shows a fourth spin accumulation element of an embodiment of the invention. The fourth spin accumulation element, unlike the first spin accumulation element, has a feature that the second spin injection part is formed on the same plane as the first spin injection part. The magnetization directions of the first magnetic conductor 3 and the second magnetic conductor 8 are antiparallel to each other. A current Ic is applied from the first spin injection part 10 to the second spin injection part 11. In the first spin injection part 10, up polarized spin electrons Is1↑ are injected into the non-magnetic conductor 1, and accumulated in the non-magnetic conductor 1 in the range of spin diffusion length. On the other hand, in the second spin injection part 11, up polarized spin electrons Is2↑ are likewise accumulated in the non-magnetic conductor 1 in the range of spin diffusion length. Since the output voltage is defined by the sum of Is1↑ and Is2↑, the output voltage of this fourth spin accumulation element is larger than the spin accumulation element having the single spin injection part.
b) shows a structure in which the second spin injection part 11 is arranged between the first spin injection part 10 and the third magnetic conductor 6. With this structure, since it is required that the second spin injection part 11 is formed between the first spin injection part 10 and the third magnetic conductor 6, it is difficult to narrow down the magnetic substance distance d1. As a result, the output voltage is decreased. Therefore, in the case where the second spin injection part is arranged on the same line as the first spin injection part, the structure of
[Numerical Expression 1]
ΔV=PiPd[λN/wNtN]ρNexp[−λN/dm]×Ic (1)
In the example 1, since two spin injection sources are arranged in the distance d1 from the third magnetic conductor 6, the output voltage of the element having the plurality of spin injection parts is specified by the total sum of spin electrons, as previously described, and can be represented as
ΔV=(Pi1+Pi2)P(λ/wNtN)ρNPi1Pdexp(−λN/d1)×Ic (2)
where the spin polarizability on the interface between the second spin injection part 11 and the non-magnetic conductor 1 is Pi2. Further, the output voltage with n spin injection parts can be represented in the following expression.
[Numerical Expression 2]
where the distance between the nth spin injection part and the third magnetic conductor 6 is dn and the current value passing through the spin injection part is Icn. Thereby, in the case where the plurality of spin injection parts are provided, the output voltage is larger than the conventional spin accumulation element having the single spin injection.
ΔV=Pd(λN/wNtN)ρN[Pi1exp(−λN/d1)+Pi2exp(−λN/d2)]×Ic (4)
Therefore, in the example 2, when d1 and d2 are narrowed down, the effects of embodiments of the invention can be sufficiently obtained.
a)-7(d) show a reproducing head having the first spin accumulation element of an embodiment of the invention.
Subsequently, a spin accumulation element using the non-magnetic conductor in the second spin injection part will be described below. A spin injection method using the non-magnetic conductor involves the use of a reversible spin Hall effect. The reversible spin Hall effect is a phenomenon in which spin electrons are polarized in the Hall direction of current to induce a flow of spin electrons (spin flow) when a current is passed through the non-magnetic conductor having great spin-orbit interaction as disclosed in “Room-Temperature Reversible Spin Hall Effect”, Physics Review Letters, T. Kimura, Y. Otani, T. Sato, S. Takahashi, and S. Maekawa, vol. 98, (2007), pp. 156601 (“non-patent document 3”).
a) is a typical view where a current Ic is applied to a non-magnetic fine line 12 (e.g., Pt or Au) having great spin-orbit interaction. When the current Ic is passed in the direction of fine line, up spin electrons and down spin electrons in the non-magnetic conductor are polarized to the end face of the non-magnetic fine line 12 owing to a strong spin-orbit interaction. Therefore, in the non-magnetic fine line 12, a difference in chemical potential is produced in the Hall direction where the current Ic flows, causing a phenomenon in which spin electrons flow.
a)-9(c) show a fifth spin accumulation element using the reversible spin Hall effect according to an embodiment of the invention. The fifth spin accumulation element has a structure in which the tunneling junction 2, the first magnetic conductor 3, and the antiferromagnetic conductor 4 are laminated successively on the non-magnetic conductor 1 as the first spin injection part 10. Also, a detection part of output voltage can detect a potential difference between the non-magnetic conductor 1 and the magnetic conductor 6 owing to a structure having the tunneling junction 5 and the magnetic conductor 6 on the non-magnetic conductor 1. The fifth spin accumulation element has a feature that the non-magnetic conductor 12 having great spin-orbit interaction is provided in the second spin injection part. The material of the second spin injection part 12 may be non-magnetic conductor having great spin-orbit interaction which is d or f metal atom or intermetallic compound such as Pt, Au, Pd or Sr2RuO4.
a), 9(b) and 9(c) are a cross-sectional view, a side view as seen from the spin injection part, and a plan view as seen from the top of the fifth spin accumulation element, respectively. The first spin injection part 10 is laminated in a film thickness direction of the non-magnetic conductor 1 and the second spin injection part 12 is electrically joined with the non-magnetic conductor 1 in a line width direction. Also, the magnetic conductor 6 for voltage detection is joined with the non-magnetic conductor 1 via the tunneling junction 5. This element has a structure in which the first spin injection part 10 and the second spin injection part 12 have a common current terminal, and currents Ic1, and Ic2 flow independently through the first and second spin injection parts. As previously described, in the first spin injection part 10, up polarized spin electrons Is1↑ are injected into the non-magnetic conductor 1. On the other hand, since the current Ic2 flows from top to bottom on the interface between the second spin injection part 12 and the non-magnetic conductor 1, as shown in
ΔVSH=αSH(Pd/wSH)ρSHexp(−d1/λN)×Ic2 (5)
(non-patent document 3), whereby, it is expected that as the line width of the non-magnetic conductor making up the second spin injection part is decreased, the output is increased.
a)-11(d) are typical views of the reproducing head having the fifth spin accumulation element.
The spin injection part of the reproducing head has a structure in which the current terminal 15, the contact 13, the non-magnetic conductor 1, the first spin injection part 10, the buffer layer 14, and the top shield 17 are laminated successively, and the second spin injection part 12 is electrically joined with the non-magnetic conductor 1, as shown in
To verify the effect of the first spin injection element of the invention as shown in
A non-local voltage measurement was conducted by passing a current Ic=1 mA through the first spin accumulation element of the invention and the conventional spin accumulation element, and applying a magnetic field in parallel to the fine line direction of the non-magnetic conductor 1 to the third magnetic conductor 6, whereby a potential difference dependent on the relative direction of magnetization between Co1 and Co3 was obtained. This potential difference ΔV is called an output voltage, and the d1 dependency of the output voltage ΔV is shown in
The conventional spin accumulation element having the single spin injection part showed a quantitatively excellent coincidence with the theoretical expression, as indicated by the broken line. On the other hand, the output voltage ΔV of the first spin accumulation element of an embodiment of the invention observed a 100% or more increase over the conventional one. This is the effect that the total of spin electrons in the non-magnetic conductor increased because the plurality of spin injection parts were provided. Also, since the magnetization directions of the first magnetic conductor and the second magnetic conductor are antiparallel, as previously described, it is considered that the mirror reflection effect of spin electrons in the non-magnetic conductor also contributes.
In the example 2, the fourth spin accumulation element of an embodiment of the invention was fabricated as shown in
In the example 3, the fifth spin injection element of the invention was fabricated as shown in
As described above, because the plurality of spin injection parts were provided, the increased output signal was confirmed as compared with the spin accumulation element having the single spin injection part. By applying the spin accumulation element of embodiments of the invention, the reproducing head having higher resolving power and higher output can be obtained.
Number | Date | Country | Kind |
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2007-323468 | Dec 2007 | JP | national |