Phase separation and sharp magnetization steps in polycrystalline Pr 1− xCa xMnO 3

Abstract

Similar to the A-site and Mn-site substitution in orbital–charge ordered (OO–CO) polycrystalline Pr 0.5Ca 0.5MnO 3, the decrease in x from x = 0.50 in Pr 1− x Ca x MnO 3 can also induce sharp magnetization steps. It has been interpreted by a martensitic-like mechanism based on phase separation. With the decrease in x , the ideal Mn 3+/Mn 4+=1:1 orbital–charge ordering will be weakened, which is due to the disorder created by the extra Mn 3+ cations. Therefore, small ferromagnetic (FM) regions with higher symmetrical structure can be induced in the antiferromagnetic (AFM) OO–CO matrix with a strongly distorted structure. Due to their different symmetry, the strains will be created at the interface between the FM regions and the AFM matrix. In a magnetic field, the FM domains cannot grow continuously because of the existence of the interfacial strains. In order to achieve their further growth, a higher magnetic field must be applied to overcome the interfacial strains. As a result, sharp magnetization steps will appear in magnetization versus magnetic field curves of Pr 1− x Ca x MnO 3. The x is smaller, the stability of the OO–CO phase is weaker, and then the interfacial strains become lower. Consequently, the critical magnetic field corresponding to the step appearance will decrease. Furthermore, the existence of the additional OO–CO state, which was recently reported by Asaka et al. [T. Asaka, S. Yamada, S. Tsutsumi, C. Tsuruta, K. Kimoto, T. Arima, T. Matsui, Phys. Rev. Lett. 88 (2002) 97201], has not been supported by our magnetic results and microscopic studies.