Seminar: "Magnetic and Volumetric Properties of Breathing Pyrochlore Magnets" by Dr. Yoshihiko Okamoto, Nagoya University
Title : Magnetic and Volumetric Properties of Breathing Pyrochlore Magnets
Speaker : Associate Prof. Yoshihiko Okamoto from Nagoya University
Breathing pyrochlore magnets, where localized spins are arranged at the edge of alternating small and large tetrahedra with magnetic interaction J and J', respectively, have attracted attention as unique systems that possess both geometrical frustration and bond alternation. In this talk, I will present magnetic properties of five A-site ordered Cr spinel compounds, LiInCr4O8, LiGaCr4O8, LiInCr4S8, LiGaCr4S8, and CuInCr4S8, where Cr3+ ions carrying an S = 3/2 spin form a breathing pyrochlore structure [1,2]. Oxides were found to have antiferromagnetic J and J' and show interesting magnetic properties, such as spin-gap like behavior due to tetramer singlet formation and a half magnetization plateau. In contrast, in sulfides, ferromagnetic interaction coexisting with antiferromagnetic interaction plays an important role in their magnetism. I will also present the thermal expansion and magnetostriction of these Cr spinel compounds . All of them showed a large volume contraction associated with antiferromagnetic order with decreasing temperature. Moreover, they show various volumetric phenomena related to their magnetism in their paramagnetic phases, such as negative thermal expansion in LiGaCr4S8.
 Y. Okamoto, G. J. Nilsen, J. P. Attfield, and Z. Hiroi, Phys. Rev. Lett. 110, 097203 (2013).
 Y. Okamoto, M. Mori, N. Katayama, A. Miyake, M. Tokunaga, A. Matsuo, K. Kindo, and K. Takenaka, J. Phys. Soc. Jpn. 87, 034709 (2018).
 T. Kanematsu, M. Mori, Y. Okamoto, T. Yajima, and K. Takenaka, J. Phys. Soc. Jpn. 89, 073708 (2020).
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