Magneto-optical study of anomalous magnetization reversal in the presence of anisotropy dispersion in CoPd thin films

Abstract

Magnetization reversal is investigated in the presence of anisotropy dispersion in weakly disordered Co x Pd 100−x (x = 23, 36, 43) thin films. A fourfold in-plane magnetic anisotropy is observed for x = 23, whereas an increase of the Co:Pd ratio induces a uniaxial anisotropy in x = 36 and 43 films. Anomalous magnetization reversal appears along the hard axes (referred to as collapse of hard axes) in x = 23 and 36 films, but disappears for x = 43. The results are consistent with the two-grain Stoner-Wohlfarth model. It is argued that the collapse of the hard axes can be controlled by intergranular exchange interaction. Quadratic magneto-optical Kerr effect (QMOKE) is also observed in the films and is found to weaken if the in-plane anisotropy is lowered through the Co:Pd ratio. QMOKE is observed for magnetic field orientations near the hard axes but not exactly along it, in agreement with the two-grain Stoner-Wohlfarth model.

Observation of recoil magnetization curves outside the major loop in Co, Fe, and Ni films

“…The kink in M(H ) predicted by our simulations is clearly present in experimental loops [see Figs. Such a behavior has previously been observed though it has remained unexplained [13,17,18].…”

“…Idigoras et al [11,12] have reproduced M RS (φ H ) very similar to ours by devising a two-grain Stoner-Wohlfarth model that mimics the partial crystalline disorder of a polycrystalline film consisting of pairs of exchange-coupled grains with misaligned anisotropy axes. It has later been used to explain the collapsed hard axis of CoPd thin films with either fourfold or twofold anisotropy [13]. We also adopted this model considering grains with magnetizations M 1 and M 2 with slightly misaligned in-plane anisotropy axes, ea 1 and ea 2 , characterized by uniaxial anisotropy constants K 1 and K 2 .…”

Chirality-Induced Noncollinear Magnetization and Asymmetric Domain-Wall Propagation in Hydrogenated CoPd Thin Films

“…By addition and subtraction of the MOKE images from the opposite directions of oblique incidence, a pure polar image and a pure longitudinal image can be obtained, respectively. 39 The hysteresis loops in the top figures which can be attributed to the tetragonal L1 0 ordering in the CoPd alloy [51][52][53] even on the short-range scale, 53,54 and to the interfacial anisotropy or strain. [55][56][57][58][59][60] Oxidation diminishes PMA, 36 but hydrogenation afterward can enhance PMA with proper hydrogen concentrations.…”

Longitudinal Magneto-Optical Kerr Effect of Nanoporous CoFeB and W/CoFeB/W Thin Films

“…As the magnetization reversal, finding the Kerr null point shall be of great interest for developing the ultrasensitive technique and the laser-induced magnetization process for potential magneto-electronic and magneto-optical device applications [24][25][26]. In addition, Kerr null points shall imply lots of information about magnetic anisotropy, exchange bias coupling, and the polarized laser-matter interaction under field since they are related to the fundamentals of magnetization reversal, the interference of reflected light, and the light-matter interaction of magnetic and/or magneto-optical thin films under a magnetic field [26][27][28]. All-optical magnetization reversal in a 20 nm thick Ni film using a circularly polarized light has been demonstrated, with a reversal speed of 260 fs, which is much faster than that in other devices, such as magnetic tunneling junctions (MTJs) and giant magnetoresistance (GMR) junctions [29].…”

“…It is beyond doubt that magneto-optical Kerr rotation reversal is particularly more complex in multilayered ferromagnetic and nonmagnetic systems with large magnetic anisotropy dispersion and an interfacial coupling effect than magnetization reversal, since the phenomena are related to light polarization, light-matter interaction, and interference of the reflected light under external field and inner magnetization of materials [24][25][26][27][28]30,33,34]. Precise regulation of this kind of MOKE rotation reversal thus becomes very important for the study of this complex phenomenon for the optimization of the microstructure and composition of magnetic thin films at nanoscale [24][25][26][27][28][29][30]33,34]. Of particular interest is the design and fabrication of special nano-structured thin films, including magnetic layers, for the regulation of MOKE rotation inverse and the related reversal mechanism study.…”