Magnetic properties of layered Ni/Cu nanowires

In this paper, the structural and magnetic properties of layered nanowires (NWs) made of alternating layers of nickel and copper were investigated. NW arrays were obtained by matrix synthesis. The nickel layers had a fixed thickness of 400 nm, and the thickness of the copper layers varied from 25 to 300 nm. The magnetic characteristics of such NWs were studied in two states: in a matrix (integral magnetic characteristics determined using vibrating sample magnetometry) and for individual NW (local magnetization visualized using MFM). For NWs in the matrix, the hysteresis loops measured for the two directions of the magnetic field become identical when the thickness of the Cu layer increases to 300 nm, which is due to the weakening of the dipole interaction between the Ni layers. The coercive force (190 Oe) and the residual magnetization (0.32 Ms) in the parallel direction of the field are maximal for the thickness of the Cu layer equal to 100 nm, which corresponds to the diameter of NWs and the distance between them. The MFM method was used to study samples with Cu layer thicknesses of 300 nm. It is demonstrated step by step how the application of an external magnetic field leads to remagnetization. An intermediate antiparallel distribution of magnetization in neighboring layers is revealed. The magnitude of the coercive force for an agglomerate of two or three NWs varies between 40-50 Oe, but the magnetization switching field turns out to be about 160 Oe, which is comparable to the coercive force for an array of NWs of this type (180-190 Oe). This demonstrates the role of the NWs' dipole interaction in the matrix.