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The field dependence of the activation volumes of nucleation and wall-motion processes in magnetization reversal of Co/Pd multilayers is presented, as observed using a magneto-optical Kerr-effect microscope capable of real-time domain imaging in a wide time range of 10-5-103 s. The analytic forms of the activation volumes are derived from a theoretical consideration of equilibrium conditions of the two typical domain evolution processes in a ferromagnetic film with uniaxial perpendicular anisotropy; the theory is shown to be in good agreement with the experimental results. It was found that the field dependence of the activation volumes can be characterized by the difference between the domain wall energy and the dipolar energy. [ABSTRACT FROM AUTHOR]

The operation of racetrack memories is based on the motion of domain walls in atomically thin, perpendicularly magnetized nanowires, which are interfaced with adjacent metal layers with high spin-orbit coupling. Such domain walls have a chiral Néel structure and can be moved efficiently by electrical currents. High-capacity racetrack memory requires closely packed domain walls, but their density is limited by dipolar coupling from their fringing magnetic fields. These fields can be eliminated using a synthetic antiferromagnetic structure composed of two magnetic sub-layers, exchange-coupled via an ultrathin antiferromagnetic-coupling spacer layer. Here, we show that nanosecond-long current pulses can move domain walls in synthetic antiferromagnetic racetracks that have almost zero net magnetization. The domain walls can be moved even more efficiently and at much higher speeds (up to ∼750 m s−1) compared with similar racetracks in which the sub-layers are coupled ferromagnetically. This is due to a stabilization of the Néel domain wall structure, and an exchange coupling torque that is directly proportional to the strength of the antiferromagnetic exchange coupling between the two sub-layers. Moreover, the dependence of the wall velocity on the magnetic field applied along the nanowire is distinct from that of the single-layer racetrack due to the exchange coupling torque. The high domain wall velocities in racetracks that have no net magnetization allow for densely packed yet highly efficient domain-wall-based spintronics. [ABSTRACT FROM AUTHOR]

Understanding the field-driven microscopic magnetization reversal in a disordered ferromagnetic (FM) film is a fundamentally intriguing issue for the application of a disorder-induced magnetic memory. We present the field dependence of the correlation between local coercivity and switching time in the FM films showing two typical reversal processes: wall-motion and nucleation dominant ones. As the applied field strength increases, the correlation coefficient in the wall-motion sample decreases, whereas the one in the nucleation sample holds nearly zero value. The change in the wall-motion sample is well explained by the transition of the magnetization reversal mechanism from a thermal activation reversal to a viscous motion. This paper shows that the magnetization reversal mechanism depending on the time scale as well as the materials has a strong influence on the correlation. [ABSTRACT FROM PUBLISHER]

In this study, we investigated the stochastic nature of domain reversal dynamics in exchange-biased IrMn/CoFe film using a time-resolved Kerr microscope. Interestingly, the statistical distributions of the magnetization half-reversal times for both forward and backward applied fields show that the magnetization reversal dynamics is much more stochastic for the backward branch, where an applied field is parallel to the exchange-bias field direction. The enhanced stochasticity is ascribed to the large degree of magnetic disorder during backward reversal, which induces discrete and random Barkhausen jumps, whereas the forward branch reversal is dominated by a thermally activated depinning process caused by a single potential barrier. This result can be explained by the asymmetry of the magnetic disorder between both branches of a hysteresis loop. [ABSTRACT FROM AUTHOR]

We have investigated the Barkhausen critical scaling behavior of NixFe1-x (x = 0-0.5) films using a magneto-optical microscope, capable of time-resolved domain observation. Real-time direct observations of the domain evolutions in these films revealed that magnetization reversal occurred with a sequence of random Barkhausen jumps. From more than 1000 repeated experiments with each sample, it was found that the distribution of the Barkhausen jump size followed a power-law distribution. The scaling exponent of the power-law distribution was found to have the same value of 1.1, independent of the film composition, revealing a universal critical scaling behavior in these alloy films. [ABSTRACT FROM AUTHOR]

Abstract: We present a systematic change of the magnetic domain structure with temperature in epitaxial ferromagnetic MnAs film on GaAs (001), observed in a wide temperature range of 15–45°C by magnetic force microscopy. Interestingly, it is found that, as temperature increases, the domain structure within the ferromagnetic α-MnAs stripes shows a mixture of head-on and simple domains at 15°C and then, takes a complete transition to simple ones above 15°C. This change could be understood by change in the demagnetizing factor of the cross-section of the ferromagnetic stripes with temperature. [Copyright &y& Elsevier]