Mössbauer spectral study of the magnetocaloricFeMnP1−xAsxcompounds

Abstract

The magnetic phase transitions in the FeMnP 1−x As x 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, F = 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 = ϳ 0.35 and ϳ210 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.

Kinetic-arrest-induced phase coexistence and metastability in(Mn,Fe)2(P,Si)

“…Hyperfine parameters obtained from the fitting are presented in Table II. The average isomer shift δ , average quadrupole splitting ε , and linewidth are in good agreement with previous reports in (Mn,Fe) 2 (P,Si)-type compounds [45][46][47]. Figure 9(a) shows the Mössbauer spectrum measured at 4.2 K for S0 after zero-field cooling.…”

“…Figure 9(a) shows the Mössbauer spectrum measured at 4.2 K for S0 after zero-field cooling. The observed sextet with broad spectral lines suggests a strong magnetic ordering with a distribution of hyperfine fields around the Fe nucleus, which can be fitted with a binomial distribution model [46]. In contrast, the 4.2 K Mössbauer spectra of S1-S3 display a complicated shape, as shown in Figs.…”

“…As a result, there are five different nearest-neighbor Fe configurations, depending on the number (from 0 to 4) of Si atoms in the tetrahedral environment. Their contributions to the Mössbauer spectrum can be described by a binomial distribution model, which has been successfully used for Mössbauer analysis in (Mn,Fe) 2 (P,Si)-type compounds [45,46]. The same fitting approach was adopted for the present study.…”

“…As revealed by the neutron diffraction results, S1 is a mixture of FM and SDW phases below 50 K. As a result, the 4.2 K Mössbauer spectra of S1-S3 can be decomposed into FM and incommensurate magnetic components. The FM component was fitted with the binomial distribution model [46], and the incommensurate magnetic component was fitted with a field-distribution model that takes into account the sinusoidally modulated Fe moment. For the incommensurate-magnetic component, the hyperfine field H SDW experienced by an Fe nucleus can be described as…”

A structural, magnetic and Mössbauer spectral study of the magnetocaloric Mn1.1Fe0.9P1−xGexcompounds

“…Because the iron-57 Mössbauer spectral study [5] of the MnFeP 1-x As x compounds has been very informative, the Mn 1.1 Fe 0.9 P 1-x Ge x compounds, with x = 0.16, 0.20, 0.22 and 0.26, have been studied herein by iron-57 Mössbauer spectroscopy combined with x-ray diffraction and magnetic measurements.…”