Ferromagnetic Ordering Along the Hard Axis in the Kondo Lattice YbIr₃Ge₇



Ferromagnetic Kondo lattice compounds are far less common than their antiferromagnetic analogs. In this Rapid Communication, we report the discovery of a ferromagnetic Kondo lattice compound, YbIr₃Ge₇. As in almost all ferromagnetic Kondo lattice systems, YbIr₃Ge₇ shows magnetic order with moments aligned orthogonal to the crystal electric field (CEF) easy axis. YbIr₃Ge₇ is unique in that it is the only member of this class of compounds that crystallizes in a rhombohedral structure with a trigonal point symmetry of the magnetic site, and it lacks broken inversion symmetry at the local moment site. The ac magnetic susceptibility, magnetization, and specific heat measurements show that YbIr₃Ge₇ has a Kondo temperature TK≈14 K and a Curie temperature T_{C}=2.4K. Ferromagnetic order occurs along the crystallographic [100] hard CEF axis despite the large CEF anisotropy of the ground-state Kramers doublet with a saturation moment along [001] almost four times larger than the one along [100]. This implies that a mechanism which considers the anisotropy in the exchange interaction to explain the hard-axis ordering is unlikely. On the other hand, the broad second-order phase transition at T_{C} favors a fluctuation-induced mechanism. © 2019 American Physical Society.


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Anisotropy, Antiferromagnetism, Crystallography, Electric fields, Ferromagnetic materials, Ferromagnetism, Iridium compounds, Magnetic susceptibility, Specific heat, Ytterbium compounds, Rhombohedral structures, Germanium compounds


Gordon and Betty Moore Foundation EPiQS Initiative through Grant No. GBMF 4417, 5305; Deutsche Forschungsgemeinschaft (DFG) Project No. BR4110/1-1; National Science Foundation under Grant No. DMR-1700030.


©2019 American Physical Society