Spin-polarized electron tunneling across magnetic dielectric

Abstract

This letter deals with a magnetic tunnel junction having spin filtering by a magnetic barrier. We performed experiments in which a relatively strong external field rotates magnetizations of both ferromagnetic electrodes in the tunnel junction with the magnetic barrier simultaneously so that the two are always parallel to each other. The tunnel magnetoresistance induced in this way was over 16% at 300 K. The angular dependency of the tunnel current on the layer magnetizations indicates that the barrier contains antiferromagnetic oxide. To achieve the described effect the magnetic electrode of the junction was oxidized prior to forming the Al 2 O 3 layer. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1925785͔Conventional spin-polarized electron tunneling is based on a tunnel junction with two ferromagnetic electrodes. [1][2][3][4][5] The tunnel current between the electrodes depends on their relative orientations of magnetization with respect to each other. 6 Spin-dependent currents can also be achieved in the case of tunneling between an antiferromagnetic electrode and a ferromagnetic one. In this case, the tunnel current changes when the magnetization vector in the ferromagnetic electrode rotates with respect to the antiferromagnetic direction of the other electrode. [7][8][9] Another approach to achieving spin-dependent tunneling was proposed in Ref. 10. To explain the concept, let us consider two ferromagnetic electrodes separated by a tunnel barrier. We assume that magnetizations M 1 and M 2 in both electrodes are always parallel. Contrary to the conventional approach, however, we consider the tunnel barrier composed of a ferromagnetic dielectric. The direction of magnetization M b in the barrier is different from the direction of magnetizations M 1 and M 2 in the electrodes. In this case, the tunnel current between the two ferromagnetic electrodes, depends on the relative direction of the spin of electrons emitted by the electrodes, with respect to the magnetization of the tunnel barrier, because the tunneling electrons see interaction with the spins of the dielectric layer through an additional exchange energy −J 1 b , where J is the exchange constant and ប 1 / 2 and ប b / 2 are electron spins in the first electrode and barrier, respectively. This either increases or decreases the effective tunnel barrier depending on the relative direction of spins in the electrodes and the ferromagnetic layer. Therefore, the tunnel current at low bias voltage V iswhere signs Ϫ and ϩ in Eq. ͑1͒ correspond to the cases of the spin directions in the tunnel barrier and in the electrodes being parallel and antiparallel to each other, respectively, provided J is positive ͑ferromagnetic exchange͒ and vice versa for negative J. G is the barrier conductivity per unit area, m is the free electron mass, is the barrier height, d is the barrier width. In writing Eq. ͑1͒, we assume 100% spin polarization at the Fermi level. If J Ӷ , then the relative change of the conductivity iswhere k eff = J ͱ 2m / ͑ប ͱ ͒ and ͗G͘ is the aver...

Anomalous Anisotropic Magnetoresistance of Antiferromagnetic Epitaxial Bimetallic Films: Mn2Au and Mn2Au/Fe Bilayers

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traditional wholly ferromagnetic (FM) spintronic devices. The fast-evolving fi eld of antiferromagnetic spintronics is being pursued on many fronts, Núñez et al studied spin torque and giant magnetoresistance (MR) in antiferromagnetic metals, [ 4 ] Hals et al derived a phenomenological theory for current-induced dynamics in antiferromagnets, [ 5 ] and Shvets et al [ 6 ] and Chshiev and co-workers [ 7 ] discussed the use of an antiferromagnetic dielectric layer as a tunneling barrier. The fast-evolving fi eld of antiferromagnetic spintronics is being pursued on many fronts, Núñez et al studied spin torque and giant magnetoresistance (MR) in antiferromagnetic metals, [ 4 ] Hals et al derived a phenomenological theory for current-induced dynamics in antiferromagnets, [ 5 ] and Shvets et al [ 6 ] and Chshiev and co-workers [ 7 ] discussed the use of an antiferromagnetic dielectric layer as a tunneling barrier.

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“…[1][2][3] The reduced stray fi elds and faster spin dynamics of antiferomagnitic elements would allow further miniaturization with less cross-talk leading to faster higher density memory. The fast-evolving fi eld of antiferromagnetic spintronics is being pursued on many fronts, Núñez et al studied spin torque and giant magnetoresistance (MR) in antiferromagnetic metals, [ 4 ] Hals et al derived a phenomenological theory for current-induced dynamics in antiferromagnets, [ 5 ] and Shvets et al [ 6 ] and Chshiev and co-workers [ 7 ] discussed the use of an antiferromagnetic dielectric layer as a tunneling barrier. More recently theoretical studies have been supported and complemented by steady experimental progress, the antiferromagnetic material IrMn has been utilized in demonstrating the possibility of producing a 100% spin-valve-like signal in an IrMnbased tunnel junction [ 8 ] and in the electrical measurement of antiferromagnetic moments in IrMn/NiFe stacks.…”

Relativistic Néel-Order Fields Induced by Electrical Current in Antiferromagnets

“…Antiferromagnets are attractive for spintronics because they offer insensitivity to magnetic field perturbations, produce no perturbing stray fields, are readily compatible with metal, semiconductor, or insulator electronic structure, can act as a magnetic memory, and can generate large magnetotransport effects [6][7][8]. For example, two distinct stable states of an AFM with orthogonal AFM spin-axis directions were set in an FeRh Ohmic resistor and shown to be insensitive to fields as high as 9 T at ambient conditions [9].…”

Magnetic characteristics of phase-separated CeO2:Co thin films

“…9,10 Another potential route for injecting spin polarized carriers into semiconductors is by using ferromagnetic tunnel barriers, which can act as a spin filter and allow only one kind of spin to tunnel into the semiconductor. [11][12][13][14][15] The feasibility of spin dependent tunneling has been demonstrated using europium chalcogenides (EuX, X: O, S, Se). 16,17 However, europium chalcogenides exhibit a T c that is much lower than room temperature, making them useless for practical device applications.…”