Magnetic and transport properties controlled by structural disorder in La0.7Ca0.3MnO3 films

Анотація

The magnetic properties of an amorphous, a partially-disordered, and a lattice-strained crystalline La_0.7 Ca_0.3 MnO₃ film are investigated. It is shown that the amorphous film exhibits Curie- Weiss-type paramagnetism with the effective magnetic moment of 4.2 m_B/Mn ion and a small ferromagnetic contribution governed by the formation of a quasi-two-dimensional crystalline interfacial inclusions. The crystalline film with nanocrystalline randomly-oriented inclusions demonstrates a superposition of ferromagnetic (in the crystalline matrix) and superparamagnetic (in the inclusions) nature. The fitted average size of the superparamagnetic particles in the case of a Langevin function is coincident with that of the nanocrystalline clusters reveated in high-resolution electron-microscopy images. An increase in the applied magnetic field leads to a reduction in the average magnetic moment of superparamagnetic particles, which is due to an enhancement of the ferromagnetic coupling between the individual randomly-oriented crystallites. The completely crystalline film undergoes only a ferromagnetic transition with a saturation magnetization at 5 K of 2.73 m_B/Mn ion.