Kirill Rivkin

Physical principles of microwave assisted magnetic recording

While the basic physics of Microwave Assisted Magnetization Reversal (MAMR) phenomenon is well established both theoretically and experimentally, its application in a practical magnetic recording environment was so far studied primarily with the help of micromagnetic recording models. In this work, we instead attempt to use analytical formulation and simple numerical models to understand the main challenges as well as benefits that are associated with such a system. It appears that the main difference between the previously introduced theory [G. Bertotti et al., Phys. Rev. Lett. 86, 724 (2001); K. Rivkin et al., Appl. Phys. Lett. 92, 153104 (2008); S. Okamoto et al., J. Appl. Phys. 107, 123914 (2010).] and recording environment is that both the RF and DC magnetic fields are applied at a substantial angle to the anisotropy axis. While the associated symmetry breaking prevents one from describing the reversal process explicitly, it is possible to approximate the solutions well enough to satisfactorily match numerical models both in the case of wire and Spin Torque Oscillator generated RF fields. This approach allows for physical explanation of various effects associated with MAMR such as high gradient of writeable anisotropy and reduction of track width, and offers a clear guidance regarding future optimization of MAMR recording.

Continuous Néel-to-Bloch transition in strips whose thickness increases: Statics and dynamics

For strips of width 2w and height h, with both exchange and the dipole-dipole interaction, we find that Neel and Bloch domain walls are locally stable. As h is increased to hc, Neel walls evolve continuously to Bloch walls by a second-order transition. It is mediated by a critical mode with , corresponding to motion of the domain wall center. A uniform out-of-plane rf-field couples strongly to this critical mode only in the Neel phase. Local, but not global stability relative to a crosstie phase was established.