Evaluation of magnetic interactions in a double-layered perpendicular magnetic recording media using ferromagnetic Hall effects

Abstract

A new method for evaluating magnetic interactions among particles in the recording layer (RL) with a soft magnetic underlayer (SUL) in a double-layered perpendicular magnetic recording media has been demonstrated. Since the RL and SUL reveal Hall effect responses with different symmetries regarding the applied magnetic field, it is possible to not only detect the anomalous Hall voltage from the RL and the planar Hall voltage from SUL simultaneously, but also to extract and evaluate their properties individually. In order to evaluate the magnetic interparticle interactions in the RL, an evaluation index of the ΔV-plot, which corresponds to the ΔM-plot, estimated using a simple relation among the initial magnetization curve, the upper and lower branch of the major hysteresis loop, was introduced. The initial magnetization curve of Co–Cr–Ta RL in a Co–Cr–Ta(100 nm)/Ni–Fe(50 nm) double-layered thin film, can be evaluated from the Hall voltage in positive and negative range of applied magnetic field using the point symmetry of the anomalous Hall voltage revealed by the RL. The negative peak in the ΔV-plot of the double layer indicated the dominance of magnetostatic interaction in the Co–Cr–Ta layer. Measurements under the canted applied field revealed field direction dependence in the estimated ΔV-plot. Adjustment of the driving current direction with respect to the in-plane projection of the applied magnetic field was found to be effective for selective rejection of the contribution from the SUL to the total Hall effect signal.

Origin of anomalously high exchange field in antiferromagnetically coupled magnetic structures: Spin reorientation versus interface anisotropy

“…[17][18][19][20]29 Fig. 8(a) shows anomalous Hall voltage (AHV) and planar Hall voltage (PHV) for the case of 0.75 nm thick Co layer exchange coupled to 17 nm (Co/Pd) multilayer.…”

“…The MR controller provides a constant current of 2 mA through the Hall bar and measures the resistance in a direction perpendicular to the current flow. The Hall voltage is obtained by multiplying the measured resistance with the applied current as shown in following equation: [17][18][19][20][21] …”

Recording media research for future hard disk drives

“…While magneto-optical methods such as MOKE are able to evaluate double-layered perpendicular media with thick RL and IL, these will also face problems for ultra-thin media films of the future due to the penetration of the incident laser deep down into the SUL. In this regard, alternative techniques that make use of the ferromagnetic or anomalous Hall effect (AHE) have been found to be effective in separating and evaluating the properties of the RL and the SUL [74,75]. This is possible due to the difference in symmetry of the contributions from the perpendicular RL moment and the in-plane SUL moment.…”