Magnetic nonextensivity on CMR manganites

Mario S. Reis 1,3Vitor S. Amaral 3Joao P. Araujo 2I. S. Oliveira 1

1. Centro Brasileiro de Pesquisas Físicas (CBPF), R. Dr. Xavier Sigaud 150 Urca, Rio de Janeiro 2229-180, Brazil
2. Departamento de Fisica and IFIMUP, Universidade do Porto (UP), Rua do Campo Alegre, 687, Porto 4169-007, Portugal
3. Universidade de Aveiro, Departamento de Fisica and CICECO (UA), Campus de Santiago, Aveiro 3810-193, Portugal


Although the number of works on CMR manganites amounts over three thousands, the models and theories developed to understand the physical properties of this materials fail to obtain plain agreement between experiment and theory. On other hand, another rather different area which has been growing at an analogous rate is the Tsallis generalized statistics, that satisfactorily describes nature if the microscopic interaction are long-ranged and the boundary conditions are fractals, as well as the system presents an intrinsic inhomogeneity. Such features have been invoked in recent models of manganites, as well as in the interpretation of experimental results. For instance, some authors emphasize a strong phase competition (inhomogeneity), and others have considered the formation of micro-cluster with fractal shapes, randomly distributed in the material, and the role of long-range interaction to phase segregation. In this direction, in two recent works [1,2] we proposed that manganites are better described within the Tsallis generalized statistics, where we obtained excellent agreement between experiment and theory. In the present work, we describe new evidences that manganites are non-extensive objects, with a model that foresee several types of magnetic anomalies presented in ferromagnetic manganites, namely: the strong downturn near the critical temperature, presented in many curves of the inverse of the susceptibility; the well know inflexion point, with hysteresis, presented in M vs. H curves near a first-order transition; the nature of the magnetic transition, i.e., if the magnetic transition is of first or second order; among others. Finally, we could also build a magnetic phase diagram that reproduce reliably all magnetic properties of the ferromagnetic manganites.
[1] M.S. Reis et al. Europhys. Lett. 58 (2002) 42.
[2] M.S. Reis et al. Phys. Rev. B 66 (2002) 134417.

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Presentation: poster at E-MRS Fall Meeting 2003, Symposium D, by Mario S. Reis
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-27 20:08
Revised:   2009-06-08 12:55
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