open access

https://doi.org/10.14943/doctoral.k13753

https://hdl.handle.net/2115/82766

正孔ドープしたパイロクロア型イリジウム酸化物 (Y1-x-yCuxCay)2Ir2O7におけるIrスピン揺らぎのミュオンスピン緩和法による研究

英語

2019-09-25

Hokkaido University

ii, 70p.

The combination of electron-electron correlation and spin-orbit coupling interaction arises the various exotic states such as spin liquid, Weyl semimetal, and topological Mott insulator. Among the pyrochlore systems, pyrochlore iridates with chemical composition, R2Ir2O7 (R = rare earth elements) having geometrically frustrated lattice exhibits mostly orderly metal-insulator transition (MIT) and is observed with accompanying magnetic transition by changing R ion. The temperature of MIT, TMI gradually decreases as increases the ionic radius of R and disappears between R = Nd and Pr. How the magnetic ordering of these R2Ir2O7 series changes in the boundary of MIT and eventually to be a possible spin liquid in Pr2Ir2O7 remains unknown so far although those have been studied intensively over the past years. Moreover, it is also necessary to understand the mechanism of MIT where the metallic state adjacent to the strongly correlated nonmetallic state by doping holes to the system. The existence of a so-called quantum critical point (QCP) where the electronic ground state is changed in the vicinity of the zero temperature and near the disappearance of antiferromagnet transition is also theoretically predicted. Magnetic properties of Ir moment are expected to play an essential role in various exotic states in R2Ir2O7. Of the pyrochlore iridates, Mott insulator Y2Ir2O7 (Y3+: non-magnetic; Ir4+: 5d5) serves as an ideal system to investigate the magnetic properties of Ir moment to clarify its origin because Y atom does not possess a local magnetic moment, no f moment/no d-f interaction (larger spin-orbit interactions) and Y2Ir2O7 also involves antiferromagnet ordering of Ir moment with all-in-all-out (AIAO) arrangement below TMI of approximately 170 K. We have initially studied the magnetic properties of Y2Ir2O7 and its hole-doped, (Y1-x-yCuxCay)2Ir2O7 with x = 0.05 and y = 0, 0.05, 0.08, 0.10, 0.20, and 0.25 by muon-spin relaxation (μSR) measurement. The synthesis of these compounds will be reported in this doctoral dissertation, as well. We also performed electrical resistivity, heat capacity, and magnetic susceptibility measurements. The magnetic transition, TN and TMI decrease with increasing value of y and seem to vanish at around y = 0.15 with x = 0.05 indicating the existence of QCP. The substitution of Ca2+ for Y3+ in hole-doped Y2Ir2O7 suppresses TN and TMI. As far as we know, we have revealed the phase diagram of hole-doped Y2Ir2O7 for the first time based on electrical transport and μSR measurements.

2019-09-25

甲第13753号

博士(理学)

(主査) 客員教授 渡邊 功雄, 教授 網塚 浩, 准教授 吉田 紘行

理学院（物性物理学専攻）

博士論文

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