Tunnelling Anisotropic Magnetoresistance Research Articles

Tunnelling anisotropic magnetoresistance at La0.67Sr0.33MnO3-graphene interfaces

Using ferromagnetic La0.67Sr0.33MnO3 electrodes bridged by single-layer graphene, we observe magnetoresistive changes of ∼32–35 MΩ at 5 K. Magneto-optical Kerr effect microscopy at the same temperature reveals that the magnetoresistance arises from in-plane reorientations of electrode magnetization, evidencing tunnelling anisotropic magnetoresistance at the La0.67Sr0.33MnO3-graphene interfaces. Large resistance switching without spin transport through the non-magnetic channel could be attractive for graphene-based magnetic-sensing applications.

Tunnelling anisotropic magnetoresistance of Fe/GaAs/Ag(001) junctions from first principles: effect of hybridized interface resonances

Results of first-principles calculations of the Fe/GaAs/Ag(001) epitaxial tunnel junctions reveal that hybridization of interface resonances formed at both interfaces can enhance the tunnelling anisotropic magnetoresistance (TAMR) of the systems. This mechanism is manifested by a non-monotonic dependence of the TAMR effect on the thickness of the tunnel barrier, with a maximum for intermediate thicknesses. A detailed scan of k∥-resolved transmissions over the two-dimensional Brillouin zone proves an interplay between a few hybridization-induced hot spots and a contribution to the tunnelling from the vicinity of the point. This interpretation is supported by calculated properties of a simple tight-binding model of the junction, which reproduce qualitatively most of the features of the first-principles theory.

An alternating alternative

The experimental demonstration of antiferromagnetic tunnelling anisotropic magnetoresistance paves the way for spintronic devices based on antiferromagnets, rather than ferromagnets.

A spin-valve-like magnetoresistance of an antiferromagnet-based tunnel junction

A spin valve is a microelectronic device in which high- and low-resistance states are realized by using both the charge and spin of carriers. Spin-valve structures used in modern hard-drive read heads and magnetic random access memoriescomprise two ferromagnetic electrodes whose relative magnetization orientations can be switched between parallel and antiparallel configurations, yielding the desired giant or tunnelling magnetoresistance effect. Here we demonstrate more than 100% spin-valve-like signal in a NiFe/IrMn/MgO/Pt stack with an antiferromagnet on one side and a non-magnetic metal on the other side of the tunnel barrier. Ferromagneticmoments in NiFe are reversed by external fields of approximately 50 mT or less, and the exchange-spring effect of NiFe on IrMn induces rotation of antiferromagnetic moments in IrMn, which is detected by the measured tunnelling anisotropic magnetoresistance. Our work demonstrates a spintronic element whose transport characteristics are governed by an antiferromagnet. It demonstrates that sensitivity to low magnetic fields can be combined with large, spin-orbit-coupling-induced magnetotransport anisotropy using a single magnetic electrode. The antiferromagnetic tunnelling anisotropic magnetoresistance provides a means to study magnetic characteristics of antiferromagnetic films by an electronic-transport measurement.

Magnetic GaAs resonant tunnelling diodes with a Mn-doped emitter

We have fabricated ferromagnetic resonant tunnelling diodes (FRTD's) based on the AlAs/GaAs/AlAs quantum wells and the p-type Mn-doped GaAs emitter layers. At low temperatures a large magnetic field dependence of the tunnelling current appears in the magnetic RTD's in rather low fields (B < 1T), which is not found in nonmagnetic RTD's. The observed decrease of current in the case of the metallic ferromagnetic emitters is explained by a tunnelling anisotropic magnetoresistance effect.

Magnetotransport of holes through an AlAs/GaAs/AlAs resonant tunnelling quantum well with a ferromagnetic Ga1–xMnx As emitter

AbstractWe have fabricated magnetic III–V compound semiconductor resonant tunnelling diodes (RTD's) based on a (Ga, Mn)As material system. The RTD's contain a ferromagnetic Mn‐doped emitter, where the Mn‐concentration was chosen on both sides of the metal–insulator (M–I) transition. The measured I –V characteristics show that large magnetoresistance (MR) is not present in non‐magnetic RTD's without the Mn‐doping. In the case of the metallic emitter the observed positive MR is interpreted as an evidence of the magnetization‐dependent tunnelling related to the exchange interaction between the hole spins and the localised spins of the 3d electrons in the ferromagnetic (Ga, Mn)As layer. Especially, the contributions from the spin‐dependent tunnelling described by the Tsu–Esaki model and from the tunnelling anisotropic magnetoresistance, which was found recently in magnetic tunnel diodes, are discussed. The measured large MR in the I –V characteristics of the magnetic RTD's, which have an emitter on the semiconducting side of the M–I transition, is explained by a simple series resistance model for the magnetic emitter, where the conduction in the Anderson localized states below the mobility edge becomes magnetic field‐dependent due to the Mn‐doping. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

TAMR effect in (Ga,Mn)As-based tunnel structures

We discuss the results of our experiments on tunnel devices based on (Ga,Mn)As structures. Those include p+-(Ga, Mn)As/n+-GaAs Esaki diodes and laterally defined narrow nanoconstrictions in (Ga,Mn)As epilayers. We found in those structures strong anisotropic magnetoresistance behaviour with features that could be attributed to the novel tunnelling anisotropic magnetoresistance effect. We argue however, that in case of nanoconstricted (Ga,Mn)As wires, some other physics has to be additionally employed to fully explain the observed effects.