Spin-dependent hopping in the paramagnetic state of the bilayer manganite $\chem{(La_{0.4}Pr_{0.6})_{1.2}Sr_{1.8}Mn_2O_{7}}$

P. Wagner; I. Gordon; V. V. Moshchalkov; Y. Bruynseraede; M. Apostu; R. Suryanarayanan; A. Revcolevschi

doi:doi:10.1209/epl/i2002-00635-7

DOI: 10.1209/epl/i2002-00635-7

Europhys. Lett., 58 (2) , pp. 285-291 (2002)

Spin-dependent hopping in the paramagnetic state of the bilayer manganite $\chem{(La_{0.4}Pr_{0.6})_{1.2}Sr_{1.8}Mn_2O_{7}}$

P. 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

Ivan.Gordon@fys.kuleuven.ac.be

(Received 23 April 2001; accepted in final form 25 January 2002)

Abstract
We report on the scaling behaviour of the colossal negative magnetoresistance effect (CMR) in a single crystal of the bilayer manganite $\chem{(La_{0.4}Pr_{0.6})_{1.2}Sr_{1.8}Mn_2O_{7}}$ . The high $\chem{Pr}$ 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 ( $T_{\ab{N}}= 50$ $\un{K}$ ) 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 $\un{K}$ . The temperature dependence $C \propto T^{-1}$ 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.

PACS
75.30.Vn - Colossal magnetoresistance.
72.20.Ee - Mobility edges; hopping transport.
75.20.-g - Diamagnetism, paramagnetism, and superparamagnetism.

© EDP Sciences 2002