Europhys. Lett., 58 (2) , pp. 285-291 (2002)
Spin-dependent hopping in the paramagnetic state of the bilayer manganiteP. Wagner1, I. Gordon1, V. V. Moshchalkov1, Y. Bruynseraede1, M. Apostu2, R. Suryanarayanan2 and A. Revcolevschi2
1 Laboratorium voor Vaste-Stoffysica en Magnetisme, Katholieke Universiteit Leuven Celestijnenlaan 200 D, B-3001 Leuven, Belgium
2 Laboratoire de Physico-Chimie de l'Etat Solide, UMR 8648 Bâtiment 414, Université Paris-Sud, F-91405 Orsay, France
(Received 23 April 2001; accepted in final form 25 January 2002)
We report on the scaling behaviour of the colossal negative magnetoresistance effect (CMR) in a single crystal of the bilayer manganite . The high content is responsible for the absence of long-range ferromagnetism and for a CMR effect in the order of 106. The system is down to the Neél temperature ( ) in a superparamagnetic state with spin clusters extending over 6-9 unit cells. The coefficient C, which describes the magnetization-induced resistance drop in the paramagnetic state, has absolute values up to C= 15 at 100 . The temperature dependence is explained by spin-dependent hopping between magnetic clusters. Spin-dependent scattering and Kondo-lattice models do not account for the magnitude of C and its variation with temperature.
75.30.Vn - Colossal magnetoresistance.
72.20.Ee - Mobility edges; hopping transport.
75.20.-g - Diamagnetism, paramagnetism, and superparamagnetism.
© EDP Sciences 2002