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PGI-1 Seminar: Prof. Dr. Tomas Jungwirth

Antiferromagnetic spintronics in footsteps of ferromagnets: From anisotropic magnetoresistance to spin torques

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01 Sep 2014 14:00
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PGI Lecture Hall

Institute of Physics in Prague, Czech Republic

Abstract:

Commercial spin-based memory and storage devices rely on one type of magnetic order, ferromagnetism, and one basic principle, that the opposite spin orientations in a ferromagnet (FM) represent the 0's and 1's. Magnetic random access memory (MRAM) is a solid-state-memory variant of the hard disk where the magnetic medium for storing and the magnetoresistive read-element are merged into one. Unlike in hard disks, the magnetic stray eld of the FM is not used for reading the MRAM bits and the latest spin{torque based MRAMs do not even use magnetic elds coupled to the FM moment for writing. From this it appears natural to consider antiferromagnets (AFMs) as active building blocks of spintronic devices, where magnetic order is accompanied by a zero net magnetic moment.


In the talk we will illustrate that AFMs may be attractive for spintronics as they oer insensitivity to magnetic eld perturbations, produce no perturbing stray elds, are readily compatible with metal, semiconductor, or insulator electronic structure, can act as a magnetic memory, can generate large magneto-transport eects, and can allow for ultrafast writing schemes. As an example we show that two distinct stable states of an AFM with orthogonal spin-axis directions can be set in an FeRh ohmic resistor and that the memory states are insensitive to elds as high as 9 T at ambient conditions. A 1% AFM anisotropic magnetoresistance (AMR) is used to electrically detect the states, in complete analogy to the 1% AMR of NiFeCo based bits in the rst generation of FM-MRAMs. Also in analogy with the development of FM spintronics, we illustrate very large ( 100%) magnetoresistance signals in AFM tunnel devices.


We will show that the AFM Neel-order spin-axis direction can be controlled indirectly by a magnetic eld via an attached exchange-coupled FM or, without the auxiliary FM, by techniques analogous to heat-assisted magnetic recording. However, as with heat-assisted FM-MRAM, the speed and energy eciency of this method are limited. We therefore conclude the talk by presenting predictions of a mechanism for AFM spin-axis reorientation by a lateral electrical current via Neel-order spin-orbit torque elds, i.e., via non-equilibrium elds that alternate in sign between the two spin sublattices. This relativistic mechanism does not involve FMs, heating, or magnetic elds, and oers ultra-short times unparalleled in FMs.

Contact

Prof. Dr. Yuriy Mokrousov
Phone: +49 2461 61-4434
email: y.mokrousov@fz-juelich.de

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