The present invention relates to magnetic-electric energy conversion devices, power supply devices, and magnetic sensors, and more particularly, to a magnetic-electric energy conversion device, a power supply device, and a magnetic sensor that utilize an electromagnetic force generated due to a magnetic field, for example.
According to the law of electromagnetic induction, an electromotive force is generated due to a temporal variation of a magnetic field. In recent years, a conversion element that converts the magnetic energy of a magnetostatic field into electric energy has been suggested (see Patent Literature 1, for example).
Patent Literature 1: International Publication WO Pamphlet 2007-15475
However, by the conversion element according to Patent Literature 1, the electromotive force generated by a conversion of the magnetic energy of a magnetostatic field into an electric energy lasts an extremely short period of time. Also, the magnitude of the electromotive force is as small as 100 μV/Tesla.
The present invention has been made in view of the above circumstances, and the object thereof is to enable generation of a long-lasting electromotive force.
The present invention provides a magnetic-electric energy conversion device that includes: a matrix that includes ferromagnetic particles with conductive properties; an injector that injects carriers into the ferromagnetic particles; and a receptor that accepts the carriers from the ferromagnetic particles, the carriers tunneling from the injector to the receptor via the ferromagnetic particles when the spins of the ferromagnetic particles are reversed by magnetic tunneling due to a magnetic field. According to the present invention, when the magnetization state of ferromagnetic particles is reversed by magnetic tunneling due to a magnetic field, carriers tunnel from the injector to the receptor via the ferromagnetic particles, so that a long-lasting electromotive force can be generated.
In the above structure, the matrix may be provided between the injector and the receptor.
The above structure may further include a barrier layer that is located at least between the matrix and the injector or between the matrix and the receptor, the barrier layer serving as the barrier for the carriers, the carriers being able to tunnel through the barrier layer.
In the above structure, the matrix and the ferromagnetic particles may be a single crystal.
In the above structure, the matrix may be GaAs, and the ferromagnetic particles may be zinc-blend-type MnAs.
In the above structure, the injector may inject carries spin-polarized in the same direction as the magnetic field, into the ferromagnetic particles.
In the above structure, the ferromagnetic particles may be nanoparticles.
The present invention provides a power supply device that includes the above magnetic-electric energy conversion device, and the power supply device supplies power through the electromotive force generated between the injector and the receptor.
The present invention provides a magnetic sensor that includes the above magnetic-electric energy conversion device, and the magnetic sensor senses the magnitude of the magnetic field through the electromotive force generated between the injector and the receptor.
The present invention provides a magnetic sensor that includes the above magnetic-electric energy conversion device, and the magnetic sensor senses the magnitude of the magnetic field through the magnetic resistance between the injector and the receptor.
The present invention enables long-time generation of an electromotive force.
The following is a description of an embodiment of the present invention.
The matrix 12 is a semiconductor or an insulator, for example, and at least has such insulation properties that carriers are always conducted from the injector 20 to the receptor 22 via the ferromagnetic particles 10. Also, the portions of the matrix 12 surrounding the ferromagnetic particles 10 preferably have insulation properties so that carriers can tunnel from the ferromagnetic particles 10 to the receptor 22. As the ferromagnetic particles 10, a ferromagnetic metal or a ferromagnetic half metal that is a ferromagnetic material and has conductive properties can be used. Also, the ferromagnetic particles preferably have a magnetic anisotropy.
The distance between the injector 20 and the ferromagnetic particles 10 is preferably such a distance that the carriers in the injector 20 can tunnel to the ferromagnetic particles 10. Likewise, the distance between the receptor 22 and the ferromagnetic particles 10 is preferably such a distance that the carriers in the ferromagnetic particles 10 can tunnel to the injector 20. Each of the ferromagnetic particles 10 preferably has such a size that the ferromagnetic particles 10 is in a magnetization state to allow magnetic tunneling. For example, the ferromagnetic particles 10 are preferably nanoparticles.
Since the ferromagnetic particles 10 are as fine as several nanometers in diameter, the magnetization state is quantized from an S-1 state to an S-4 state and so on, and from a −(S-1) state to a −(S-2) state and so on. The energy difference from the level in a quantized adjacent portion (the energy difference between the S state and the S-1 state, for example) is 2 gμBSHa. Here, Ha represents A/gμB. In a case where the ferromagnetic particles 10 are extremely small, magnetic tunneling through the magnetic barrier occurs so that the magnetization state of the ferromagnetic particles 10 transits from the −S state to the S state.
As described above, according to this embodiment, when the magnetization state of the ferromagnetic particles 10 is reversed by magnetic tunneling due to a magnetic field, carriers tunnel from the injector 20 to the receptor 22 via the ferromagnetic particles 10. Accordingly, the magnetic energy of a magnetostatic field can be converted into electric energy. Also, the time constant of magnetic tunneling can be made as long as 100 seconds or longer. Therefore, the electromotive force generated by a magnetostatic field can be maintained for a longer period of time than that of Patent Literature 1. Also, the magnitude of the electromotive force is S times as large as that of Patent Literature 1. For example, where S is approximately 200, the electromotive force reaches 20 mV/Tesla.
A barrier layer (the tunnel barrier 14 or 16, for example) that can serve as a barrier for carriers and allow carriers to tunnel therethrough is preferably provided at least between the matrix 12 and the injector 20 or between the matrix 12 and the receptor 22, so that carriers conducted to the receptor 22 do not return to the injector 20. Also, a Coulomb blockade effect is used so that the carriers do not return to the injector 20 via the ferromagnetic particles 10. Therefore, the ferromagnetic particles 10 are preferably nanoparticles. The size (the diameter, for example) of the ferromagnetic particles 10 are preferably several nanometers.
The following is a description of examples of this embodiment.
After the p-type GaAs layer 42 is grown, the substrate temperature is lowered to 240° C., and a 10-nm thick Ga0.94Mn0.06As layer is formed on the p-type GaAs layer 42. An AlAs barrier layer 48 is formed on the Ga0.94Mn0.06As layer by MBE. The film thickness of the AlAs barrier layer 48 is 2.1 nm. A GaAs spacer layer 50 is formed on the AlAs barrier layer 48 by MBE. The film thickness of the GaAs spacer layer 50 is 1 nm. After that, the substrate temperature is increased to 480° C. in the MBE chamber, and a 20-minute heat treatment is performed. Through the treatment, a GaAs matrix layer 44 containing MnAs ferromagnetic particles 46 is formed from the Ga0.94Mn0.06As layer. The film thickness of the GaAs matrix layer 44 is 10 nm. The ferromagnetic particles 46 are MnAs having a zinc-blend-type crystal structure, and are approximately 2 to 3 nm in diameter.
A MnAs ferromagnetic layer 52 is formed on the GaAs spacer layer 50 by using MBE. The film thickness of the MnAs ferromagnetic layer 52 is 20 nm, and has a NiAs hexagonal crystal structure. An Au electrode is formed on the MnAs ferromagnetic layer 52. The structure extending from the Au electrode 54 to the p-type GaAs layer 42 has a cylindrical mesa-like shape, and the radius of the cylindrical structure is 100 μm. The side faces of the mesa are covered with an insulating film.
In
When a 480° C. heat treatment is performed at 550° C. or higher, the MnAs ferromagnetic particles 46 become a NiAs crystal structure, but does not become a zinc-blend-type crystal structure. Also, the GaAs spacer layer 50 is preferably provided to increase the film quality of the MnAs ferromagnetic layer 52.
In
In the example, the matrix layer 44 and the ferromagnetic particles 46 are one single crystal, or a single zinc-blend-type crystal, for example. With this structure, the coupling between spins and electrons is strong. Also, a co-tunneling phenomenon to simultaneously cause spin-state magnetic tunneling and carrier tunneling easily occurs as described with reference to
Particularly, the matrix layer 44 and the ferromagnetic particles 46 are preferably a III-V semiconductor. With this arrangement, the matrix layer 44 and the ferromagnetic particles 46 can be readily formed as a single crystal. Further, the ferromagnetic particles 46 can be easily formed, as the matrix layer 44 is made of GaAs while the ferromagnetic particles 46 are made of MnAs. As the matrix layer, a compound semiconductor such as AlGaAs or an elementary semiconductor such as Si or Ge can be used. As the ferromagnetic particles 46, a metal such as Cr, As, Fe, or Co, or a compound ferromagnetic material can be used.
To generate a Coulomb blockade effect, the ferromagnetic particles 10 are preferably nanoparticles. The diameters of the ferromagnetic particles 10 are preferably 10 nm or smaller, and more preferably, 3 nm or smaller.
The injector 20 may be a ferromagnetic layer containing Fe or Co or the like, other than MaAs. Further, as described with reference to
In the example, a power supply device that supplies power through the electromotive force Vemf generated between the Au electrode 54 and the GaAs substrate 40 (or between the injector 20 and the receptor 22 in the embodiment) can be provided. With the device, power can be supplied from a magnetostatic field.
Also, since the magnitude of the electromotive force Vemf is determined by the magnitude of the magnetic field H, a magnetic sensor that senses the magnitude of the magnetic field through the electromotive force Vemf generated between the Au electrode 54 and the GaAs substrate 40 can be provided. Accordingly, a magnetic sensor that senses the magnitude of a magnetic field, without applying a current with the use of an external power supply like a Hall element, can be provided.
Further, as shown in
Although a preferred example of the present invention has been described, the present invention is not limited to the specific example, and various modifications and changes may be made to the example within the scope of the claimed invention.
10 ferromagnetic particles
12 matrix
14, 16 tunnel barrier
20 injector
22 receptor
40 substrate
42 p-type GaAs layer
44 matrix layer
46 ferromagnetic particles
48 barrier layer
50 spacer layer
52 ferromagnetic layer
54 Au electrode
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2010/053668 | 3/6/2010 | WO | 00 | 12/23/2011 |
Number | Date | Country | |
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61158129 | Mar 2009 | US |