Anomalous thermal hysteresis in magnetization and resistivity of La_1-xSr_xMnO₃

We have investigated thermal hysteresis of magnetization and resistivity in La_1-xSr_xMnO₃ (0.5≤x≤0.6) with an A-type antiferromagnetic structure. For 0.52≤x≤0.56, the magnetization curve exhibits a counterclockwise (CCW) thermal hysteresis about T_N, while the resistivity curve shows a clockwise (CW) thermal hysteresis. On the other hand, samples with 0.58≤x≤0.6 exhibit CCW thermal hystereses in both magnetization and resistivity curves. Remarkably, for x = 0.58 the rotational direction of thermal hysteresis of resistivity changes from CCW to CW by the magnetic field. This anomalous hysteretic behavior is explained by the competing interaction between the three-dimensional (3D) metallic ferromagnetic and two-dimensional (2D) metallic A-type antiferromagnetic phases.