Critical exponents for the ferromagnetism in colossal magnetoresistance manganites

Abstract

Critical phenomena of ferromagnetic transition in colossal magnetoresistance manganites are theoretically studied. Concerning the critical exponents for this transition, there still remains controversy among experimental results. In order to clarify intrinsic physics of the manganites through a comparison with theoretical prediction, we investigate the critical phenomena of double-exchange models by using finite-size scaling analysis on unbiased numerical results. As a result, we show that the critical exponents of the ferromagnetic transition of the three-dimensional double-exchange model is consistent with those of the Heisenberg model, but are distinct from the mean-field one.

Monte Carlo study of the critical behavior and magnetic properties of La2/3Ca1/3MnO3 thin films

“…They investigated the critical phenomena of doubleexchange models for manganites by using finite size scaling analysis on unbiased numerical results. These results were in agreement with those obtained by Heisenberg models [6]. Nevertheless, they did not consider manganites as thin films, which actually have much technological interest.…”

“…This characteristic is related with a new interesting observed ferromagnetic transition in doped manganites [4,5]. Recent refinement of the experimental techniques and the improvement of the sample quality have made possible to discuss critical phenomena of this transition in detail [6]. Particularly, for the purpose of capturing some of the physics underlying these materials associated to magnetic and critical phenomena, the critical exponents and the universality class have been investigated by various experimental methods.…”

“…This fact makes necessary to shed some light on this issue from the theoretical standpoint. One theoretical work was presented by Furukawa and Motome [6]. They investigated the critical phenomena of doubleexchange models for manganites by using finite size scaling analysis on unbiased numerical results.…”

Three-dimensional Ising critical behavior inR0.6Sr0.4MnO3(R

“…The way this might affect the description of the critical behavior is still a question to be developed from the theoretical point of view. Bear in mind that if a ferromagnetic system is simply and fully described by the double-exchange mechanism, theory assesses that it should be described by the 3D-Heisenberg model [8]. This implies that the description of these ferromagnetic transitions is much more complex than thought.…”

“…We have selected this particular concentration (substituting 40% the rare-earth ion with Sr) as it is the one at which the colossal magnetoresistance (CMR) is especially important and for which the low temperature phase is ferromagnetic in the whole temperature range [6,7]. It can be seen from the phase diagrams that both Pr 1−x Sr x MnO 3 and Nd 1−x Sr x MnO 3 are very similar in the region around x = 0.4 (paramagnetic insulator above T C , ferromagnetic metallic under it, with close values of T C ) so the study of the critical behavior of both of them using the same techniques and under the same conditions could give valuable information about the appropriateness of a physical description simply by means of a double exchange interaction, which would be described by a Heisenberg model [8] or if any other mechanisms must be taken into account, such as magnetic anisotropies, disorder, dipolar interactions, phase separation, and such.…”