Suppression of Curie temperature through severe shear strain in lanthanum manganite LaMnO3+ δ

The effects of severe shear stress on the electron-transfer-induced ferromagnetism of lanthanum manganite LaMnO3+δ have been investigated. Shear stress was applied via high-pressure torsion (HPT) processing and controlled by varying the number of rotations N. A decrease of 30 K in the Curie temperature TC was observed under shear strain, in contrast to hydrostatic compression, which increases TC. Examination of the x-ray diffraction patterns revealed an increase in the unit-cell volume, indicating negative pressure. A correlation between the decrease in TC and the increase in lattice parameter a was observed. A decrease in the valence state of Mn after HPT processing was also confirmed via x-ray photoelectron spectroscopy. Thereby, the valence change, as well as defect insertion and lattice strain, weakens the double-exchange interaction. This underscores the potential of shear strain as a platform for tuning electron-transfer-induced ferromagnetism and for strain engineering in LaMnO3+δ.