A study on composed nonextensive magnetic systems

authors	Navarro, FAR; Reis, MS; Lenzi, EK; Oliveira, IS
nationality	International
journal	PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS
author keywords	manganites; non-extensive statistics; partial trace
keywords	COLOSSAL MAGNETORESISTIVE MANGANITES; STATISTICAL-MECHANICS; EVIDENCES; BEHAVIOR
abstract	We investigate the magnetic properties of a composed nonextensive system. The work is motivated by recent proposals that manganites are magnetically nonextensive objects, according to Tsallis statistics. We consider a two-parts composed system, A-B (both spins 1/2), and calculate 2 self-consistently the partial magnetizations in the mean field approximation, M-A and M-B, for the cases the coupling between the subsystems is either ferro or anti-ferromagnetic. This involves the notion of partial trace in the nonextensive statistics. For temperatures below the magnetic ordering temperatures, and q not equal 1, we found strong disagreement between the M vs. T curves calculated from the total 4 x 4 Hilbert space, through rho(q), when compared to the calculation made from the 2 x 2 subspaces, if we use the usual definition rho(A(B)) = Tr-B(A)(rho), and then elevates the matrices to the qth power, as adopted in other contexts in the literature of the nonextensive statistics. On another hand, full agreement is found if we take rho(A(B),q) = Tr-B(A)(rho(q)), remaining q an implicit parameter. (C) 2004 Elsevier B.V. All rights reserved.
publisher	ELSEVIER SCIENCE BV
issn	0378-4371
year published	2004
volume	343
beginning page	499
ending page	504
digital object identifier (doi)	10.1016/j.physa.2004.05.074
web of science category	Physics, Multidisciplinary
subject category	Physics
unique article identifier	WOS:000224495900034