Frustrated minority spins in GeNi₂O₄

¹  Quantum Beam Science Directorate, Japan Atomic Energy Agency - Tokai, Ibaraki 319-1195, Japan
²  Department of Physics, Korea University - Seoul, Korea
³  HANARO Center, Korea Atomic Energy Research Institute - Daejeon, Korea
⁴  The Institute for Solid State Physics, University of Tokyo - Kashiwa, Chiba 277-8581, Japan
⁵  Graduate School of Frontier Sciences, University of Tokyo - Kashiwa, Chiba 277-8561, Japan
⁶  RIKEN (The Institute of Physical and Chemical Research) - Wako, Saitama 351-0198, Japan
⁷  CREST, Japan Science and Technology Corporation - Saitama 332-0012, Japan
⁸  Department of Physics, University of Virginia - Charlottesville, VA 22904, USA
⁹  Department of Applied Physics, Waseda University - 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
¹⁰  Department of Physics, Cornell University - Ithaca, NY 14853-2501, USA

Corresponding author: shlee@virginia.edu

Received: 29 November 2007
Accepted: 18 March 2008

Abstract

Recently, two consecutive phase transitions were observed, upon cooling, in an antiferromagnetic spinel GeNi₂O₄ at T=12.1 K and T=11.4 K, respectively (Crawford M. K. et al., Phys. Rev. B, 68 (2003) 220408(R)). 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 T the spins on the 111 kagome planes order ferromagnetically in the plane and antiferromagnetically between the planes (phase I), leaving the spins on the 111 triangular planes that separate the kagome planes frustrated and disordered. At the lower T, 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.