MAGNETOCALORIC EFFECT IN SOME Fe(2)P LIKE COMPOUNDS
Résumé
The magnetocaloric effect (MCE) of the series Fe(2-x)M(x)P (M = Ru, Rh, Pd, Pt) as well as that of MnRhAs, all compounds crystallizing in the Fe(2)P type hexagonal structure, have been analysed. Fe(2)P exhibits a first order ferro - (F) to paramagnetic (P) transition at T(c) = 217 K where a well defined MCE was measured. In order to increase the ordering transition towards room temperature, selected metal substitutions to iron were shown to operate well. For the ferromagnetic Fe(2-x)M(x)P compounds the increase of T(c) was shown to depend on the nature and the content of the M element. The largest effect occurs with M = Rh, and e.g. for Fe(1.75)Rh(0.25)P, the Curie temperature reaches 310 K. However, a decrease of the magnetocaloric effect was observed, which fairly agrees with the parallel decrease of the overall magnetisation, reference to that of Fe(2)P. MnRhAs is antiferromagnetic (AF) at low temperatures. Between the AF and P states, it exhibits F state in a narrow range of temperature. The overall magnetisation increases markedly with the applied field. For instance, under 2 T the transitions AF - F and F - P occur close to 160 and 200 K respectively. A large magneto-caloric effect has been observed at the AF - F transition which is of first order type and not at the second order F-P one. For instance at 160 K the magnetocaloric effect is up to 2 K, when a field of 2 T is adiabatically applied. Discussion of both the crystal structure thermal characteristics as well as the most pertinent aspects of the magnetic structures will be established, reference made also to the main principles governing the MCE in the parent MnFeP(1-x)As(x) system.