Quasi-static Reversal Research Articles

Resonant Switching of Two Dipole-Coupled Nanomagnets

The storage layer of recently developed spin-flop magnetic random-access memory consists of two closely spaced dipole-coupled nanomagnets and is highly stable in the ground state as well as in quasistatic fields applied off the easy axis. We show experimentally and confirm by using micromagnetic simulations that these spin-flop bilayers can be switched relatively easily by dynamic fields, applied at the frequency of the optical spin resonance of the bilayer. The field amplitude sufficient for this resonant switching can be an order of magnitude lower than the fields necessary for quasistatic reversal. Our data and micromagnetic analysis suggest that thermal agitation can play a role in the observed resonant switching behavior.

Nonequilibrium Domain Pattern Formation in Mesoscopic Magnetic Thin Film Elements Assisted by Thermally Excited Spin Fluctuations

The dynamic behavior in the evolving pattern of thermally assisted, nonequilibrium domains in magnetic thin-film elements undergoing ultrafast 180 degrees magnetization reversal was studied. Magnetization reversal enters a fully dynamic regime when the external field conditions are changed much faster than the sample is able to respond. The dynamic pathway develops a complexity not seen in quasistatic reversal but still retains a high level of order with well-developed dynamic domain patterns formed in response to subnanosecond transitions of the external applied magnetic field.

Blocking and locking during rotational magnetization reversal in ferromagnetic thin films

A model describing quasi-static partial rotation and dynamic noncoherent rotation is presented and shown to agree with experiment. It is shown that, with applied field rise times longer than 1 ns, the ripple can be expected to relax in equilibrium with the rotating means magnetization. Magnetostatic stray fields prevent blocking from strongly affecting the rotational process and permit a stable ripple configuration even beyond the critical astroid. At a defined applied field threshold the inhomogeneous portion of the effective field from uniaxial anisotropy and applied field overcomes the stabilizing effects of the magnetostatic stray fields in alternate half-wavelengths of the ripple causing the magnetization there to switch through a large angle. The predicted large angle switching of the magnetization in alternate half wavelengths of the ripple is in good agreement with experimentally observed bands or stripes of reversed and unreversed magnetization both during quasi-static reversals in inverted Permalloy films and during dynamic non-coherent rotation with applied field rise times longer than 1 ns in normal Permalloy films. The model presents a reasonable fit to the field dependence of the angle between the observed stripes and the uniaxial anisotropy axis. Magnitudes of the local anisotropy causing the ripple are obtained from the fit to the data and shown to agree with the values determined by transverse susceptibility measurements.

An analysis of the quasi-static reversal of magnetization in two-layer films taking into account the effect of the surface binding energy

An analysis is made of the quasi-static reversal of magnetization of two-layer films separated by a dielectric layer, based on the theory of uniform rotation, taking into account the effect of the binding energy, which arises due to the wave-like topography of the ferromagnetic-dielectric boundary surfaces. Theoretical hysteresis loops are given. These are compared with hysteresis loops taken from two-layer films consisting of FeNiMo-Fe separated by a layer of SiO.