A structural phase transition induced by an external magnetic field

Direct Observation of Percolation in a Manganite Thin Film

Upon cooling, the isolated ferromagnetic domains in thin films of La0.33Pr0.34Ca0.33MnO3 start to grow and merge at the metal-insulator transition temperature TP1, leading to a steep drop in resistivity, and continue to grow far below TP1. In contrast, upon warming, the ferromagnetic domain size remains unchanged until near the transition temperature. The jump in the resistivity results from the decrease in the average magnetization. The ferromagnetic domains almost disappear at a temperature TP2 higher than TP1, showing a local magnetic hysteresis in agreement with the resistivity hysteresis. Even well above TP2, some ferromagnetic domains with higher transition temperatures are observed, indicating magnetic inhomogeneity. These results may shed more light on the origin of the magnetoresistance in these materials.

Reversible structural transition in epitaxial manganite film

A reversible structural transition of an epitaxial La(2/3)Sr(1/3)MnO3 film deposited on a LaAlO3 substrate has been investigated by means of in situ high-resolution transmission electron microscopy and electron diffraction, combined with image and diffraction calculations. We observe that the crystallographic symmetry of the film can be lowered via electron beam irradiation, leading to a rhombohedral-monoclinic transition. This transition can be attributed to the cooperating effect of the mismatch stress and the irradiation-induced thermal stress.

Close correlation between the magnetic moments, lattice distortions, and hybridization in LaMnO3 and La(1-x)Sr(x)MnO3+delta: doping-dependent magnetic circular X-ray dichroism study

The first observation of a magnetic circular x-ray dichroism (MCXD) at the Mn L2,3 core edges in antiferromagnetic LaMnO3 shows canted spin and orbital ( m(orb)) moments arising from lattice distortions. An L2,3-edge MCXD in ferromagnetic metals and insulators, La1-xSr(x)MnO3+delta, reveals that m(orb) of Mn strongly depends on x in the metallic regime but remains unchanged with the metal-to-insulator transition (x approximately 0.16). An O K-edge MCXD, which shows m(orb) of O caused by 2p-3d hybridization, is much larger in the ferromagnetic metal than insulator phases, sharply contrasting with m(orb) of Mn. Our findings indicate a close magnetism-lattice-hybridization coupling.

Direct magneto-optical observation of a structural phase transition in thin films of manganites

The spontaneous formation of twins in La(2/3)Ca(1/3)MnO3 films below T(S) approximately 105 K is observed by a magneto-optical technique. The twins are revealed as stripes along the {110} directions where magnetization tilts out of the film plane due to the stresses in twins. Their appearance is associated with a martensitic phase transition in the film triggered by the cubic-to-tetragonal transition in the SrTiO3 substrate. It is found that magnetization of the films proceeds by inhomogeneous rotation of magnetic moments. This is due to the presence of microscopic structural inhomogeneities. Their dominating role in the low-temperature transport can explain small effects of the transition at T(S) on the resistivity.