Magnetic phase diagram of the magnetocaloric compound MnFeSi

We have studied the magnetic phases of single-crystalline Mn3Fe2Si3 by neutron diffraction and magnetization measurements. Within the series Mn5−xFexSi3, an inverse magneto-caloric effect (MCE) has been observed for x=0, while for x=4 a moderately high direct MCE occurs [1]. Similarly to the parent compound Mn5Si3, Mn3Fe2Si3 exhibits two antiferromagnetic phase transitions to an AF1 and AF2 phase, respectively. The transition from AF1 → AF2 gives rise to an inverse MCE, i.e. the magnetic entropy is increased by the application of a magnetic field, albeit with complex field and temperature dependences. We discuss these changes in light of the preferential replacement of Mn by Fe on one of the two distinct lattice sites of the crystal structure (space group P63/mcm at RT). This leads to an increase in the transition temperatures and critical fields when compared to Mn5Si3. In addition, we find hints for ferromagnetic short-range correlations, which persist at temperatures twice as high as the Neel temperature. [1] Songlin et al, J. Alloys Compd, 334, 249−252 (2002