Giant magnetoresistance and topological Hall effect in the EuGa4antiferromagnet.

We report on systematic temperature- and magnetic field-dependent studies of the EuGa4binary compound, which crystallizes in a centrosymmetric tetragonal BaAl4-type structure with space groupI4/mmm. The electronic properties of EuGa4single crystals, with an antiferromagnetic (AFM) transition atTN∼ 16.4 K, were characterized via electrical resistivity and magnetization measurements. A giant nonsaturating magnetoresistance was observed at low temperatures, reaching∼7×104% at 2 K in a magnetic field of 9 T. In the AFM state, EuGa4undergoes a series of metamagnetic transitions in an applied magnetic field, clearly manifested in its field-dependent electrical resistivity. BelowTN, in the ∼4-7 T field range, we observe also a clear hump-like anomaly in the Hall resistivity which is part of the anomalous Hall resistivity. We attribute such a hump-like feature to the topological Hall effect, usually occurring in noncentrosymmetric materials known to host topological spin textures (as e.g., magnetic skyrmions). Therefore, the family of materials with a tetragonal BaAl4-type structure, to which EuGa4and EuAl4belong, seems to comprise suitable candidates on which one can study the interplay among correlated-electron phenomena (such as charge-density wave or exotic magnetism) with topological spin textures and topologically nontrivial bands.

Depinning of domain walls in permalloy nanowires with asymmetric notches.

Effective control of the domain wall (DW) motion along the magnetic nanowires is of great importance for fundamental research and potential application in spintronic devices. In this work, a series of permalloy nanowires with an asymmetric notch in the middle were fabricated with only varying the width (d) of the right arm from 200 nm to 1000 nm. The detailed pinning and depinning processes of DWs in these nanowires have been studied by using focused magneto-optic Kerr effect (FMOKE) magnetometer, magnetic force microscopy (MFM) and micromagnetic simulation. The experimental results unambiguously exhibit the presence of a DW pinned at the notch in a typical sample with d equal to 500 nm. At a certain range of 200 nm < d < 500 nm, both the experimental and simulated results show that the DW can maintain or change its chirality randomly during passing through the notch, resulting in two DW depinning fields. Those two depinning fields have opposite d dependences, which may be originated from different potential well/barrier generated by the asymmetric notch with varying d.

Pure spin-Hall magnetoresistance in Rh/Y3Fe5O12 hybrid.

We report an investigation of anisotropic magnetoresistance (AMR) and anomalous Hall resistance (AHR) of Rh and Pt thin films sputtered on epitaxial Y(3)Fe(5)O(12) (YIG) ferromagnetic insulator films. For the Pt/YIG hybrid, large spin-Hall magne toresistance (SMR) along with a sizable conventional anisotropic magnetoresistance (CAMR) and a nontrivial temperature dependence of AHR were observed in the temperature range of 5-300 K. In contrast, a reduced SMR with negligible CAMR and AHR was found in Rh/YIG hybrid. Since CAMR and AHR are characteristics for all ferromagnetic metals, our results suggest that the Pt is likely magnetized by YIG due to the magnetic proximity effect (MPE) while Rh remains free of MPE. Thus the Rh/YIG hybrid could be an ideal model system to explore physics and devices associated with pure spin current.