Frustrated minority spins in GeNiO

Matsuda, Masaaki; Chung, J.-H.*; Park, S.*; Sato, Taku*; Matsuno, Kenichiro*; Katori, Hiroko*; Takagi, Hidenori*; Kakurai, Kazuhisa; Kamazawa, Kazuya*; Tsunoda, Yorihiko*; Kagomiya, Isao*; Henley, C. L.*; Lee, S.-H.*

Recently, two consecutive phase transitions were observed, upon cooling, in an antiferromagnetic spinel GeNiO at K and K, respectively. Using unpolarized and polarized elastic neutron scattering we show that the two transitions are due to the existence of frustrated minority spins in this compound. Upon cooling, at the spins on the 111 kagom planes order ferromagnetically in the plane and antiferromagnetically between the planes (phase I), leaving the spins on the 111 triangular planes that separate the kagom planes frustrated and disordered. At the lower , the triangular spins also order in the 111 plane (phase II). We also present a scenario involving exchange interactions that qualitatively explains the origin of the two purely magnetic phase transitions.