Mössbauer Spectral Study of the Magnetocaloric FeMnP₁₋ₓAsₓ Compounds

Raphaël P. Hermann
O. Tegus
E. Brück
Gary J. Long, Missouri University of Science and Technology
Fernande Grandjean, Missouri University of Science and Technology
K. H. J. Buschow
F. R. de Boer

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The magnetic phase transitions in the FeMnP1−xAsx compounds with x= 0.25, 0.35, 0.45, 0.50, and 0.55, have been studied by iron-57 Mössbauer spectroscopy. The ferromagnetic and antiferromagnetic spectra have been analyzed with a model that takes into account the random distribution of the P and as near-neighbor anions of a given iron site. This distribution is a binomial distribution of the contributions to the spectra of each iron with n as near neighbors. A magnetostriction model has been used to characterize the temperature induced paramagnetic to ferromagnetic first-order phase transition and order parameters, ηF=2.6 , 2.3, 2.0, 1.57, and 1.43 have been obtained for x=0.25 , 0.35, 0.45, 0.50, and 0.55, respectively. A detailed phase diagram has been derived from the Mössbauer spectral analysis and reveals a magnetic triple point at x=∼0.35 and ∼210 K . A model that takes into account the random binomial P and as distribution and the contribution from the iron and manganese magnetic sublattices yields excellent fits of the spectral components assigned to the ferromagnetic and incommensurate antiferromagnetic components for the x=0.25 and 0.35 compounds at all temperatures.