Influence of pressure on the stability of the magnetically ordered states in alloys of the system Mn2−xFexAs0.5P0.5

Abstract

The phase diagram of the system Mn2−xFexAs0.5P0.5 under pressure is investigated experimentally and theoretically. It is found that the spontaneous and magnetic-field-induced low-temperature phase in the region 0.5⩽x<0.8 does not suffer significant changes under hydrostatic pressure up to 2kbar. Based on ab initio calculations of the electronic structure of the alloys Mn1.5Fe0.5As0.5P0.5, it is established that the degree of filling of the 3d electron band changes upon ferromagnetic polarization and compression of the crystal lattice. A model is proposed by which one can take into account the main features of the antiferromagnetic and canted ferromagnetic structures. The parameters of the model are the degree of filling of the d band, the nonmagnetic electronic density of states, and the intra-atomic exchange integral. Their values are estimated directly from the data of the first-principles electronic structure calculations. It is shown in the framework of the model that the stability of the magnetic characteristics of the canted ferromagnetic structure with respect to pressure is due to an increase of the number of electrons in the magnetically active band upon a decrease of the unit cell volume.

Magnetic field induced order–order phase transition in magnetocaloric systems Mn2−xFexAs0.5P0.5 and MnFeAsyP1−y

“…Here, the saturation magnetization of the induced phase (as seen in Fig. 2b) is almost a half of the maximum value of saturation magnetization of FM state, which is spontaneous in the Mn 1.2 Fe 0.8 As 0.5 P 0.5 sample [6,12].…”

“…In the system with cation substitution, M exp (x) and M FM (x) are in agreement only in the range of 0.8 rx r1.1. The qualitative divergence of the curves for x o0.8 can point the formation of a canted structure with spontaneous magnetization in the range of 0.6 rxo0.8 and preserved in a wide range of magnetic field strength (in particular, under the induced order-order transitions for x ¼0.5 [6]). The origin of an intermediate magnetic structure between FM and AF states in the system with the cation substitution, which is absent in the system with anion substitution, may be due to qualitative differences of concentration dependences of d-band occupation.…”

“…Also we should note a slight increase of the number of d-electrons in ferromagnetic and nonmagnetic N NM d 4N FM d phases as y decreases (Table 1). The results of our calculation [6] of the electronic characteristics M FM (x), N FM d ðxÞ,N NM d ðxÞ, combined with the experimental dependences V(x), M exp (x) for Mn 2À x Fe x As 0.5 P 0.5 with cation substitution, are given in Fig. 5…”

“…1. Magnetic phase diagrams of the MnFeAs y P 1 À y (a) [6] and Mn 2 À x Fe x As 0.5 P 0.5 (b) [7]. T C is Curie temperature, T N is Neel temperature, and T 1 is the temperature of order-order (FM-AF) phase transitions.…”

“…The nature of the giant magnetocaloric effect in magnetic-field-induced order-order phase transitions is less transparent, since the change of magnetic entropy in the transitions changing only the type of magnetic order may be small. Then, the existence of magnetocaloric effect is determined by an additional contribution to the entropy change made by the magnetoelastic interaction [5] or by highly different degree of disorder in magnetic phases [6]. Many compounds demonstrate magnetic phase transitions of both types accompanied by a giant magnetocaloric effect.…”