## Doctors Philosophiae Honoris Causa

Yuriy Alexandrovich Izyumov is an outstanding theoretician in solid state physics. For all his life he worked at the Institute of Physics of Metals (IPM) of Ural Branch of Russian Academy of Sciences (RAS), where he started in 1959 after his postgraduate study at Ural State University. In 1960 he got his PhD under supervision of academician S.V. Vonsovsky and in 1967 he became Doctor of Sciences. He has founded and for many years was the head of the Department of Mathematical and Theoretical Physics of IPM.

Yuriy Izyumov has started his scientific carrier at IPM working on the theory of scattering of slow neutrons in magnetic ordered crystals. This topic became important due to the fast development of research on nuclear reactors and use of neutron beams in condensed matter physics. In 1966 his first book Magnetic Neutronography was published (in collaboration with R.P. Ozerov). It was the first book on this topic in the world literature and for many years since then was a desk book for experimentalists around the world.

Yuriy Izyumov has contributed significantly into the development of magnetic neutronography. He has developed theory of scattering of polarized neutrons on complex magnetic structures, applied symmetry theory to the problems of magnetic neutronography, and obtained the exact solution of the problem of neutron diffraction on soliton lattice. On the basis of his results in Poland was issued a fundamental handbook on magnetic structures with symmetry analysis of each structure. In 1968 for this work he and co-authors were awarded the State Prize of the USSR. This research is closely related with the theory of phase transitions in magnetically ordered crystals. Izyumov has suggested an idea of exchange multiplets and applied it to phase transitions in magnetics. These studies are summarized in his book Phase Transitions and Symmetry of Crystals, published also in English.

The main topic of Izyumov studies was quantum theory of magnetism. As far as in 60s he has developed a comprehensive theory of magnetic ordered crystals with impurities. He has predicted existence of a quasi-local state in the magnon spectrum of crystals with weakly bound impurities. An exact solution of the problem of two impurity atoms with antiferromagnetic binding, placed in ferromagnetic matrix, has allowed to explain anomalous physical properties of compounds with mixed exchange interaction.

Yuriy Izyumov has contributed also into the development of mathematic tools in the theory of magnetic systems. In late 60s he has developed a convenient diagram method for spin operators, and, later, for operators used in the problems of strongly correlated electron systems (so called Hubbard operators). These operators obey complicated commutation relations as comparing with those of conventional Fermi- and Bose-operators, which causes mathematical difficulties in describing spin systems and strongly correlated systems. During the last years Isyumov has suggested a method of generating functional for the description of such systems. This method allows to derive equations for temperature Green functions in terms of variational derivatives with respect to fluctuating fields. Within this approach he has formulated a generalized approximation of chaotic phases. It has allowed to solve the problem of fluctuations of longitudinal spin components in isotropic ferromagnetic, to build the magnetic phase diagram for strongly correlated metal models and to show the possibility of formation of superconducting state with high temperatures of superconducting transition.

Izyumov used to generalize the information in research areas he was working at. For 40 years he has published 16 comprehensive reviews in Uspekhi Fizicheskikh Nauk (Physics-Uspekhi) on various problems of Solid State Physics. He has published 5 books most of which are translated into English. He also was an excellent lecturer. For 25 years he was a professor at Ural University, and among his disciples there are 6 doctors of sciences. For his pedagogical activity Izyumov was awarded a S.V. Vonsovsky Gold Medal. Izyumov was a member of the Presidium of Ural Branch of RAS. He was a head of the scientific council of physical and technical sciences.

In 2006 Yuriy Izyumov was elected a member of Russian Academy of Sciences. In 2010 he became a Doctor Philosophiae Honoris Causa at Bogolyubov Institute for Theoretical Physics of National Academy of Sciences of Ukraine.