Very Large Tunneling Anisotropic Magnetoresistance of a(Ga,Mn)As/G

Abstract

We report the discovery of a very large tunneling anisotropic magnetoresistance in an epitaxially grown (Ga,Mn)As/GaAs/(Ga,Mn)As structure. The key novel spintronics features of this effect are as follows: (i) both normal and inverted spin-valve-like signals; (ii) a large nonhysteretic magnetoresistance for magnetic fields perpendicular to the interfaces; (iii) magnetization orientations for extremal resistance are, in general, not aligned with the magnetic easy and hard axis; (iv) enormous amplification of the effect at low bias and temperatures.

Anisotropic magnetoresistance in nanocontacts

“…1,2 The transport counterpart of MAE is anisotropic magnetoresistance ͑AMR͒, i.e., the dependence of the resistance on the angle between the magnetization and the current flow. Whereas AMR in bulk was known back in the 19th century and is a rather small effect, the recent observation of AMR in a variety of low dimensional systems, [3][4][5][6][7][8][9][10][11][12] largely exceeding bulk values, has opened a new research venue in the field of spin-polarized quantum transport. Very large AMR has been reported in planar tunnel junctions ͓tunneling anisotropic magnetoresistance ͑TAMR͔͒ with a variety of electrode and barrier materials.…”

“…Very large AMR has been reported in planar tunnel junctions ͓tunneling anisotropic magnetoresistance ͑TAMR͔͒ with a variety of electrode and barrier materials. [3][4][5][6][7][8] Enhanced AMR has also been observed in atomic sized contacts, both in the tunnel regime ͑TAMR͒ and in the contact ͑or ballistic 13 ͒ regime ͓ballistic anisotropic magnetoresistance ͑BAMR͔͒, 14 for Py, 9 Fe, 10 Ni, 11 and Co. 12 Additionally, GaMnAs islands in the Coulomb blockade regime show electrically tunable AMR. 15 Thus, a wide range of nanostructures made from different materials display enhanced AMR.…”

Spin-Dependent Phenomena in (Ga,Mn)As Heterostructures

“…Moreover, as it has been shown in [32], the anisotropy of TMR results from the anisotropy of the current in the AFM configuration. Thus, our model does not explain the TAMR effect, which consists of a strong dependence of tunneling current on the direction magnetization in the TMR junctions in the FM configuration, as reported for some structures [10,11].…”

“…Recently, it was also reported that the magnetoresistance of the (Ga,Mn)As-based tunnel junctions is very sensitive to the direction of applied magnetic field. This so-called tunnel anisotropic magnetoresistance (TAMR) effect was observed when the saturation magnetization direction was changed in-plane [9][10][11] as well as when it was turned perpendicular to the magnetic layer [11,12]. It was also shown that the magnetization vectors of consecutive (Ga,Mn)As ferromagnetic layers separated by nonmagnetic spacers in a multilayer structure are correlated by an interlayer coupling [13][14][15][16][17] and structures exhibiting giant magnetoresistance (GMR) were obtained [14].…”

Spin‐dependent tunneling in modulated structures of (Ga,Mn)As

“…This so-called tunnel anisotropic magnetoresistance (TAMR) effect was observed in structures containing a single ferromagnetic electrode 11,12 as well as in typical TMR MTJ with two ferromagnetic contacts. 13,14 These challenging experimental findings call for a theory that would describe the tunneling in semiconductor MTJs and would indicate the ways for optimized design of the devices. Since the ferromagnetic coupling in (Ga,Mn)As is mediated by the holes, 1,6 a meaningful theory has to take into account the entire complexity of the valence band, including the spin-orbit interaction.…”