Magnetic Phase Transition and Microstructure in Manganite
– Direct Observations by Electron Holography and Lorentz Microscopy –

Yasukazu Murakami, Hiroto Kasai, Joong Jung Kim, Mamishin Shuichi, Daisuke Shindo, Shigeo Mori and Akira Tonomura

Abstract: The nucleation and growth mechanism of the ferromagnetic phase inside the charge ordered insulator state of La_0.25Pr_0.375Ca_0.375MnO₃, which is a typical manganite showing colossal magnetoresistance, was studied by electron holography and Lorentz microscopy.  Cryogenic Lorentz microscopy observations revealed a zig-zag interface that separated the ferromagnetic phase from the non-magnetic mother phase.  The results indicated a significant pinning effect for the motion of phase boundary, and the pinning forces originated from the structural antipathy between the ferromagnetic phase and the charge-ordered state.  We also determined magnetic parameters, such as the magnetocrystalline anisotropy constant, by using the electron microscopy observations.

Key words: electron holography, Lorentz microscopy, colossal magnetoresistance, magnetic domain, magnetic domain walls