Specific features of pulse and quasi-static remagnetization and relaxation properties of Nd$_{0.5}$Sr$_{0.5}$MnO$_3$ single crystals

The hysteresis features in the behavior of the magnetization and resistance of Nd$_{0.5}$Sr$_{0.5}$MnO$_3$ single crystals in quasi-static (up to 9 T) and pulsed (up to 14 T) magnetic fields have been studied. Relaxation processes of magnetization and resistance after the action of a magnetic field of 9 T have also been investigated. It has been shown that relaxation curves are approximated by two exponents with different time constants, which are related to relaxation of the metastable ferromagnetic phase towards two different antiferromagnetic crystal structures ($I_{mma}$ and $p2_1/m$). Mechanism of the phase transitions antiferromagnetic insulator $\leftrightarrow$ ferromagnetic metal (AFM/I $\leftrightarrow$ FM/M) and existence of a high-conductive state of a sample after removal of magnetizing field in the temperature range below 150 K is proposed. The mechanism is determined by the structural transition, which is induced by a magnetic field (due to magnetostriction), and by a slow relaxation of the FM-phase (larger volume) to the stable AFM-phase (smaller volume) after field removal. It has been shown that, during pulse magnetization at the temperature 18 K, the time required for the AFM/I $\to$ FM/M phase transition is six–seven orders of magnitude shorter than that for the FM/M $\to$ AFM/I phase transition.