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Spintronics

Hitachi Cambridge Laboratory

Left : Scanning electron micrograph image and schematics of a combined spin Hall transitor device with two detecting Hall crosses H1 and H2 and one gate placed before cross H1 and the second gate placed behind cross H1 and before cross, H2. Gates and p-side of the lateral p-n junction are highlighted in red. The focused laser beam is indicated by the yellow spot.

Right : Demonstration of the spin AND logic function by operating both gates (input signals) and measuring the response at Hall cross H2 (output signal). Measured data at cross H1 are also shown for completeness. (Figure is taken from Ref. [4].)


    Our spintronics research investigates spin-orbit interaction related effects and is performed in strong collaborations with various partners worldwide. Beside internal collaboration within Hitachi we are working with groups from the Institute of Physics ASCR in Prague (Czech Republic), the Microelectronics Research Centre from the University of Cambridge (UK), the University of Nottingham (UK), the Texas A&M University in College Station (USA) and the Institut d'Electronique Fondamentale in Orsay (France).
    Spintronics involves the study of active control and manipulation of spin degrees of freedom in a solid state system. [1, 2] Conventional spintronic devices, used already in computer hard drive read heads or magnetic random access memories are controlled by externally applied magnetic fields or electrical currents. However, anticipating spintronics for low-power applications requires new concepts, such as electric field control of magnetization or generation and manipulation of pure spin currents for data transfer and processing. Indeed, the realization of a viable semiconductor transistor and information processing devices based entirely on the electron spin has fueled intense basic research of three key elements: injection, detection, and manipulation of spins in the semiconductor channel. The inverse spin Hall effect (iSHE) detection of spins injected optically in a 2D GaAs [3] and manipulated by a gate-voltage dependent internal spin-orbit field has led to the experimental realization of a spin transistor logic device. [4] We also recently demonstrated the iSHE spin current detection combined with an electrical spin injection and manipulation by electrically controlled drift, realizing a spin current amplifier [5].
    Apart from spincurrent based devices, we are developing novel concepts where spin-orbit coupling affects material properties such as the density of states, the chemical potential and the magnetic anisotropy. Studies in this field lead to the first realization of the antiferromagnetic tunneling anisotropic magnetoresistance [6] enabling the study of antiferromagnetically ordered moments in IrMn exchange coupled to NiFe [7] and opening the window to ultra-high-speed antiferromagentic spintronics where magnetization dynamics is dominated by the strong exchange interaction between antiferromagnetically coupled moments. Moreover, the potential of electric field controllable antiferromagntic semiconductors with high Néel temperatures [8] makes antiferromagnetic spintronics to a promising candidate for future device applications. Another example is the Coulomb blockade Anisotropy Magnetoresistance (CBAMR) based on the magnetic anisotropy of the chemical potential. [9] We recently utilized this effect to demonstrate spin-gating of the charge flow in a nonmagnetic aluminum single electron transistor with a ferromagnetic gate realizing a spin transistor operating without spin current [10]. Spin-orbit driven magnetic resonance in magnetic nanodevices [11] and electric field control of domain wall motion [12, 13] highlight additionally the potential of spin-orbit interaction related effects for a new generation of magnetic probe, memory and logic devices.


References :

  1. I. Zutic, J. Fabian and S. Das Sarma, S. Rev. Mod. Phys. 76, 323 (2004), Spintronics: Fundamentals and applications
  2. C. Chappert, A. Fert and F. Nguyen Van Dau, Nature Materials 6, 813 (2007), The emergence of spin electronics in data storage
  3. J. Wunderlich, et al., Nature Phys. 5, 675 (2009), Spin-injection Hall effect in a planar photovoltaic cell
  4. J. Wunderlich, et al., Science 330, 1801(2010), Spin Hall Effect Transistor
  5. K. Olejnik, et al., Phys. Rev. Lett. 109, 076601 (2012) Detection of Electrically Modulated Inverse Spin Hall Effect in an Fe/GaAs Microdevice
  6. B. G. Park , et al., Nature Materials 10, 347 (2011), A spin-valve-like magnetoresistance of an antiferromagnet-based tunnel junction
  7. X. Marti, et al., Phys. Rev. Lett. 108, 017201 (2012), Electrical measurement of antiferromagnetic moments in exchange-coupled IrMn/NiFe stacks
  8. T. Jungwirth, et al., Phys. Rev. B 83, 3, 035321 (2011), Demonstration of molecular beam epitaxy and a semiconducting band structure for I-Mn-V compounds
  9. J. Wunderlich, et al., Phys. Rev. Lett. 97, 7, 077201 (2006), Coulomb blockade anisotropic magnetoresistance effect in a (Ga,Mn)As single-electron transistor
  10. C. Ciccarelli, et al., Appl. Phys. Lett. 101, 122411 (2012), Spin gating electrical current
  11. D. Fang, et al., Nature Nanotechnology 6, 413 (2011), Spin-orbit-driven ferromagnetic resonance
  12. P. Roy, et al., Appl. Phys. Letts. 99, 122504 (2011), In-plane magnetic anisotropy dependence of critical current density, Walker field and domain-wall velocity in a stripe with perpendicular anisotropy
  13. E. de Ranieri, et al., Nature Materials 12, 808-814 (2013) Piezoelectric control of the mobility of a domain wall driven by adiabatic and non-adiabatic torques


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