Regensburg 2019 – wissenschaftliches Programm
PRV IV: Preisträgervortrag
Dienstag, 2. April 2019, 13:15–13:45, H1
Is room temperature magnetism possible without d or f electrons? — •Michael Coey — School of Physics, Trinity College Dublin, Ireland --- Laureate of the Max-Born-Prize 2019
There are numerous reports of 'ferromagnetic-like' magnetization curves originating from materials that do not possess the d or f electrons that are normally associated with ferromagnetic order. The data are characterized by an absence of the temperature dependence and coercivity that generally accompany magnetic order. The saturation magnetization may be orders of magnitude less than the extrapolated saturation filed. Progress towards understanding the phenomenon hinges on finding out what promotes/destroys the phenomenon. Three oxide examples are presented: CeO2 nanoparticles (La-doping/nanoparticle separation); SrTiO3 surfaces (reduction or pulverization/tiron surface treatment); nanoporous amprphous alumina (pore area/salycylic acid treatment), The data establish that surface defects are responsible. Two explanations are considered 1) a spin-split ferromagnetic defect-related impurity band and 2) giant orbital paramagnetism due to coherent electronic state associated with zero-point fluctuations of the vacuum electromagnetic field. The second seems to be more likely.