2008/06/18 by Motohiko Tanaka, Tanaka, Motohiko, Hirohiko Kono +3
Physics and Astronomy · #FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #cond-mat.mtrl-sci
paper · pdf · doi:10.48550/arxiv.0806.3055
6 pages, 8 figures
arxiv created 2009/02/13 · arxiv updated 2009/12/01
The mechanism of rapid and selective heating of magnetic metal oxides under the magnetic field of microwaves which continues beyond the Curie temperature Tc is identified by using the Heisenberg model. Monte Carlo calculations based on the energy principle show that such heating is caused by non-resonant response of electron spins in the unfilled 3d shell to the wave magnetic field. Small spin reorientation thus generated leads to a large internal energy change through the exchange interactions between spins, which becomes maximal around Tc for magnetite \rm Fe3\rm O4 . The dissipative spin dynamics simulation yields the imaginary part of the magnetic susceptibility, which becomes largest around Tc and for the microwave frequency around 2 GHz. Hematite \rm Fe2\rm O3 with weak spontaneous magnetization responds much less to microwaves as observed in experiments. The heating of titanium oxide by microwave magnetic field only when oxygen defects are present is also explained by our theory in terms of the absence of spontaneous magnetization.