Prof. Vladimir Khovaylo, National University of Science and Technology, Russia
Biography: Prof. Vladimir Khovaylo received M.S. degree from M.V. Lomonosov Moscow State University, Russia, in 1997 and Ph.D. degree from Tohoku University, Japan, in 2002. In 2010 he defended habilitation thesis (Dr. Ing. habil.) at M.V. Lomonosov Moscow State University. He was a JSPS Fellow at National Institute of Advanced Industrial Science and Technology, Japan (2002-2004) and a senior researcher at Institute of Radioengineering and Electronics of Russian Academy of Sciences (2004-2009) before joining National University of Science and Technology “MISiS”, Russia, where he is currently a professor of materials science and a deputy director of the Centre for Energy Efficiency Research and Education. He was visiting professor at University of Duisburg-Essen, Germany (2006), Oviedo University, Spain (2007), invited professor at Tohoku Gakuin University, Japan (2008), and JSPS distinguished researcher (2010) and visiting professor (December 2017 – February 2018) at Tohoku University, Japan. In 2016 he was recognized as the Best Research Professor of the National University of Science and Technology “MISiS”. From 2017, Prof. Khovaylo is corresponding member of the International Thermoelectric Academy. His research interests include ferromagnetic shape memory alloys, Heusler compounds and nanostructured thermoelectric materials.
Title: Compensated Ferrimagnetism in Heusler Alloys
The intense experimental and theoretical search for materials with high dynamic characteristics (speed of domain walls, frequencies of natural spin vibrations) has been motivated by the development of new magnetic systems for recording and processing information with increased recording density and speed. In this context, antiferromagnets could be of considerable interest because their spin dynamics are expected to be much faster than that of ferromagnets. However, ordinary antiferromagnets are not suitable materials for this aim because the equivalency of two magnetic sublattices wipes out the effects which are important for spintronic devices. Fortunately, the problems inherent of antiferromagnets can be solved by using ferrimagnets in which, for some values of external parameters (e.g., temperature), the magnetization of the sublattices can cancel each other, which is called the phenomenon of magnetization compensation or spin compensation. In the vicinity of the spin compensation point, the dynamics is similar to antiferromagnetic and the domain walls velocity and the frequency of spin vibrations increase .
From an experimental point of view, the phenomenon of spin compensation can be observed in a wide class of Heusler alloys. Design of X2YZ Heusler-based compensated ferrimagnets is based on the combination of the Slater-Pauling rule, which states that the magnetic moment is determined by the valence electron numbers and the Kübler rule, which ascribes a high local magnetic moment to the Mn atoms at Y position . Alongside with the X2YZ Heusler alloys, this approach has been found to be applicable for tetragonal Mn3Z (Z = Ga, Al, Ge), which can be considered as Heusler-like Mn2MnZ systems . Among the X2YZ Heusler alloys, the most intensively studied alloys were those with X = Mn. Magnetism of these alloy systems can be easily tuned by partial substitution of Mn atoms with a non-magnetic element thus adjusting the difference in magnetization of the two magnetic sublattices to zero value. Examples of successful realization of the compensated ferrimagnetism in Heusler alloys shall be outlined in the presentation. Impact of the structural ordering on the magnetization compensation shall be discussed for the case of ordinary and inverse Heusler structure.