Nanosecond magnetization reversal of highly coercive FePt with pulsed microcoils: experiments and modelling

摘要

As magnetization reversal speeds in applications approach the nanosecond range and recording media with high anisotropies to increase bit density are envisioned, there is a need to study the switching of high coercivity materials at short timescales. Most studies to date focus either on materials with a low magnetocrystalline anisotropy or on μs times scales and longer. A way to produce magnetic fields that are strong and fast at the same time, is to drive very short current pulses through very small coils. The coils used in this work consist of a single turn of a 30μm thick copper film with a core diameter of 50μm. Due to the small size of the system and the low inductance of the coil, current rise times of less than 10ns are possible and peak magnetic fields can reach 50T [1], while the energy stored in the capacitor bank is only of the order of 0.1J. This system is well suited to study the magnetization reversal of highly anisotropic FePt of the L1{sub}0 phase, which is seen as a promising candidate for future high density magnetic recording due to its low critical grain size for superparamagnetism and its corrosion resistance. The FePt films studied here were grown epitaxially by pulsed laser deposition on MgO(100) substrates at 800°C and have coercivities above 5T in static measurements at room temperature [2]. Figure 1 shows the magnetic field pulse and the response of the magnetization of a 40nm thick FePt film with perpendicular anisotropy μ{sub}0H{sub}C=5.5T). A fast polar Kerr effect setup is employed to measure the magnetization response to the external field. The magnetization is switched by the rising edge of the field pulse and switched back by the falling edge, which reaches into the negative range, as the system behaves as an under-damped oscillator.