Frustrated minority spins in GeNi2O4M. Matsuda1, J.-H. Chung2, S. Park3, T. J. Sato4, K. Matsuno5, H. Aruga Katori6, 7, H. Takagi5, 6, 7, K. Kakurai1, K. Kamazawa8, Y. Tsunoda9, I. Kagomiya9, C. L. Henley10 and S.-H. Lee8
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
received 29 November 2007; accepted in final form 18 March 2008; published May 2008
published online 24 April 2008
Recently, two consecutive phase transitions were observed, upon cooling, in an antiferromagnetic spinel GeNi2O4 at TN1=12.1 K and TN2=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 TN1 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 TN2, 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.
75.10.Jm - Quantized spin models.
75.25.+z - Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source, X-ray scattering, etc.).
75.50.Ee - Antiferromagnetics.
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