Ferromagnetic ordering of linearly coordinated Co ions in LiSr${}_2$[CoN${}_2$]

Abstract

LiSr${}_2$[CoN${}_2$] single crystals were successfully grown out of Li-rich flux. Temperature- and field-dependent measurements of the magnetization in the range of $T=2-300$ K and up to ${\mu }_0\text{H}=7$ T as well as measurements of the heat capacity are presented. Ferromagnetic ordering emerges below $T_C=44$ K and comparatively large coercivity fields of ${\mu }_{0}H=0.3$ T as well as pronounced anisotropy are observed upon cooling. Polycrystalline samples of the Ca analog LiCa${}_2$[CoN${}_2$] were obtained and investigated in a similar way. In both compounds Co manifests orbital contributions to the magnetic moment and large single-ion anisotropy that is caused by second-order Spin-orbit coupling. Quantum chemistry calculations reveal a magnetic anisotropy energy of 7 meV, twice as large as the values reported for similar Co $d^8$ systems.

21 pages, 6 figures, 5 tables