Yousuke Norizuki | Searcharxiv

arXiv2013

A Superparamagnetic State Induced by a Spin Reorientation Transition in Ultrathin Magnetic Films

We investigate a spin reorientation transition (SRT) in ultrathin magnetic films by Monte-Carlo simulations. We assume that the lateral size of the film is relatively small and it has a single-domain structure. To gain insights into the SRT, we measure a free-energy as a function of perpendicular and in-plane magnetizations. As a result, we find that the system is in a superparamagnetic state at the SRT temperature. The disappearance of magnetization around the SRT temperature, which is observed in experiments, emerges due to dynamical fluctuations in magnetization which are inherent in the superparamagnetic state. This observation is in contrast to that in large ultrathin magnetic films that the disappearance of magnetization is caused by a static magnetic structure with many complex domains.

cond-mat.mtrl-sci↗

arXiv2013

Penetration of a magnetic wall into thin ferromagnetic electrodes of a nano-contact spin valve

We theoretically analyzed a magnetic wall confined in a nano-contact spin valve paying special attention to the penetration of the magnetic wall into thin ferromagnetic electrodes. We showed that, compared with the Bloch wall, the penetration of the Neel wall is suppressed by increases of the demagnetization energy. We found the optimal conditions of the radius and height of the nano-contact to maximize the power of the current-induced oscillation of the magnetic wall. We also found that the thermal stability of the Bloch wall increases when the nano-contact's radius increases or height decreases.

cond-mat.mes-hall↗