Characterization of transitions in MnFeP_0.45As_0.55 compound

The resistance, magnetization and strain measurements have been carried out on MnFeP_0.45AS_0.55 compound. We found that, at variance with what is commonly believed, the critical temperature points for the first order transition, paramagnetism-ferromagnetism transition, and lattice anomaly are not identical. The first order transition goes on in a quite wide temperature range with a thermal hysteresis of about 10 K. In the duration of the first order transition, the paramagnetism-ferromagnetism transition is observed, which indicates that they are not related to the lattice anomaly. Thus, we attribute it to the continuous change of the lattice parameters due to the structure transition based on our observation and Zach et al.'s work. On the other hand, the lattice anomaly occurs at lower temperature than that of the first order structural and magnetic transitions. We conclude that it is a magnetostrictive behavior associated with the magnetoelastic coupling below the Curie temperature.