Dec 06, 2012
from 02:30 PM to 04:00 PM
|Contact Name||Kimberly Cole|
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The majority of spintronics devices can be associated with one of the two basic physical paradigms of the field. The first paradigm stems from Mott's two-spin-channel picture of transport in ferromagnets and the second paradigm is due to Dirac's quantum-realistic spin-orbit coupling.
The essential distinction between functionalities of the two types of spintronics devices is that the "Mott" devices rely on relative magnetization orientations of separate ferromagnetic components and on transport of electron's spin between the components. For example, commercial spintronic devices, used in modern hard-drive read heads and magnetic random access memories, are magnetic spin valve structures comprising two ferromagnetic electrodes whose relative magnetization orientations is switched between parallel and antiparallel configurations, yielding the desired giant or tunnelling magnetoresistance effect . The "Dirac" spintronic devices, on the other hand, rely on a single self-sustaining spin-orbit coupled component with their transport characteristics governed by the subtle effects resulting from the spin-orbit coupling.
Starting from the anisotropic magnetoresistance effect (AMR) present in the ohmic transport regime of bulk ferromagnets, I will discuss magnetotransport anisotropy in the tunnelling and in the Coulomb blockade single electron transport regimes. The Tunneling Anisotropic Magneto Resistance (TAMR) is an interface effect and arises from the dependence of the relativistic tunneling density of state on the orientation of the magnetic moments. [2, 3] Another class of "Dirac" spintronic devices have the magnetotransport characteristics coded in a single quantity derived directly from the relativistic band structure: the magnetization-orientation dependent chemical potential. In one particular realization of the concept, the spin-orbit coupled magnet is placed in a single-electron transport channel and the chemical potential controls the huge Coulomb blockade anisotropic magnetoresistance (CBAMR) of the channel. [4-6] Another realization is a new type of a spin-transistor in which the magnet is completely removed from the transport channel and placed to the capacitively coupled gate.
An important property of "Dirac" spintronic devices based effects is that they are equally present in antiferromagnetically ordered systems.
Antiferromagnets (AFM) have been used in spintronics devices so far only to pin the magnetization direction of a ferromagnetic electrode through the exchange-bias effect. Recently, the antiferromagnetic TAMR in a tunnel junction with an AFM electrode of IrMn and a nonmagnetic counter electrode was realized.  The magnetization direction of the AFM IrMn layer was manipulated with a relatively small magnetic field of 50mT by the exchange spring effect of coupled soft NiFe. Moreover, the AFM TAMR provides a means to study the exchange-bias effect by an electronic transport measurement.
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