Local Magnetic Properties MnFePSi .pdf
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Local Magnetic Properties of MnFeP0.5Si0.5 and Mn1.4Fe0.6P0.3Si0.7
Piotr Fornal1, Jan Stanek2, Sonia Haj-Khlifa3, Ryszard Zach1, Patricia de Rango3 and Daniel Fruchart3
Institute of Physics, Technical University of Cracow, Podchorążych 1, 30-084 Cracow, Poland
Marian Smoluchowski Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348
Institut Néel, CNRS, BP 166, 38042, Grenoble Cedex 9, France
Corresponding author: P. Fornal, tel. 12 637 06 66, fax 12 637 14 46, firstname.lastname@example.org
The ternary compounds MnFeP0.5Si0.5 and Mn1.4Fe0.6P0.3Si0.7 have been studied by using
Mössbauer spectroscopy between 84 and 310 K. The spectra reveal the distribution of the
hyperfine magnetic fields acting on Fe in tetrahedral 3f site of the Fe2P-type crystal structure.
The influence of the local non-metal P and Si, and metal Mn and Fe coordinations of the Fe
local magnetic properties have been established.
Keywords: Magnetic phase transitions; Mössbauer spectroscopy; Magnetocaloric effect
The ternary compounds (Mn,Fe)2(Si,P) belong to a novel class of materials exhibiting
high level magneto-caloric properties [1-3] which are promising for environment friendly
cooling systems. The search for experimental modifications of the magnetic properties of Fe2P
the base material by selecting optimal compositions with a maximal variation of magnetic
entropy at transition was the subject of many reports during the last two decades [2- 5]. The
magnetic properties in temperature ranging close to RT, where the compounds can exhibit
ferro-, antiferro- and paramagnetic properties, strongly depend on the Mn/Fe/Co ratios [6-8]
which are modulated as well by substitutions of As, Ge, Si to P [2, 4, 9-14]. The compounds
here investigated, MnFeP0.5Si0.5 and Mn1.4Fe0.6P0.3Si0.7 crystallize with the hexagonal crystal
structure Fe2P-type (SG:P-62m). The metal atoms occupy two different sites, a tetrahedral (t)
non-metal coordination 3f position and a pyramidal (p) non-metal coordination 3g position,
the non-metal element occupying the 1b and 2c positions, as shown Fig. 1.
Fig. 1. Crystal structure of Fe2P. The two Fe sites (p) and (t), and the two P sites are shown.
Firstly, the effect of 50% substitution of Si to P atom at the 1b position (P-62m
structure) on the atomic magnetic properties of Fe in MnFeP1-xSix is analyzed. In MnFeP0.5Si0.5,
Fe occupies exclusively the 3f position (t sites) and conversely Mn occupies the 3g position (p
sites) according to [9, 10, 15-16]. Secondly, the modification of the local Fe magnetic states
by nearest non-metal neighbors was studied with a second Mn1.4Fe0.6P1-xSix compound where
40% of Fe in 3f position is substituted by Mn and parallel more Si is substituted to P, thus
occupying mainly the 2c position [12, 16].
Samples were synthesized from appropriated amount of 99.9% purity elements.
Powders of starting elements were mixed, finely crushed in a mortar and introduced in
evacuated silica tubes, then heated step by step up to 500°C and further progressively heated
up to 850°C for 8 days. A final heat treatment was performed by high frequency heating,
allowing melt the samples before rapidly cooling down. XRD patterns were recorded (BraggBrentano mode, λCu-Kα) to characterize the crystalline state of the samples, demonstrating
The Mössbauer spectra were recorded in transmission geometry in a bath cryostat at
temperatures T = 310, 250, 200, 150 and 84 K. The temperature stabilization was 0.1 K. The
recorded spectra were fitted using the MOSSMOD program assuming two or three local Fe
sites, characterized by isomer shift and quadrupole splitting values; for each of the sites, a
sum of Gaussian distributions of the magnetic hyperfine field was assumed.
Both compounds resulting spectra and the corresponding distributions of hyperfine
fields are shown in Figs. 2 and 3. The hyperfine parameters and characterization of the
distributions of the hyperfine field are collected in Tables 1 and 2.
For MnFeP0.5Si0.5, the distribution of the magnetic field can be effectively well fitted by
two Gaussians with different Isomer Shifts. In addition, a small contribution (~7 %) of
paramagnetic fraction was evidenced to take place in data recorded above 150 K.
The spectra of Mn1.4Fe0.6P0.3Si0.7 appear much more complicated. Anyway, at 84 K the
distribution of the magnetic field can be reproduced by three components with significantly
different average magnetic fields. Between 150 and 250 K, the spectra consist of one
magnetic and two paramagnetic contributions. At 310 K, the compound appears fully
In MnFeP0.5Si0.5, Fe which was found only and fully occupying the 3f tetrahedral
position (t)  may be coordinated by 4, 3, 2, 1 and 0 Si or P atoms. These different nonmetal configurations modify only weakly the hyperfine magnetic field, but they influence the
s-electron density at Fe nuclei as similarly reported for MnFeP1-xAsx [9-11] also confirmed
later [12, 13].
The role of the Fe neighboring metal atoms is determining for the iron magnetic
polarization. In Mn1.4Fe0.6P0.3Si0.7, the Fe atom in 3f position has 2 nearest Fe neighbors in (t)
sites at ~ 2,69 Å  so that three different local configurations can be distinguished. These
correspond successively to 1 - two Fe neighbors with a probability of 0.6*0.6 = 0.36, 2 - two
Mn neighbors with a probability of 0.4*0.4 = 0.16 and 3 - Fe and Mn neighbors with a
probability of 2*0.6*0.4 = 0.48. The Mn atoms exclusively form the next nearest and nextnext nearest metal neighboring, as located on 3g positions (p) sites, as univocally defined
shells. To the three local configurations defined here above corresponds three different
hyperfine fields as measured at 84 K. The component of which hyperfine field is ~ 21 T
should be assigned to a Fe-Fe-Fe configuration, as found for MnFeP0.5Si0.5. However, since the
latter component is the most intense one (47 %), it can be anticipated that the distribution of
Mn atoms over the 3f positions (p sites) is not fully random and local Fe-rich and Mn-rich
arrangements are preferred. It is worth to note, that for Mn1.4Fe0.6P0.5As0.5 similar three magnetic
subspectra were found , but having comparable intensities. The Mn atoms in the 3f
position weaken the exchange couplings in between the Fe magnetic moments and then lower
the Curie temperature comparison made with that of Mn0.5Fe0.5P0.5As0.5, a trend in agreement
with the magnetic susceptibility measurements of ref. .
A Mössbauer analysis of the parent MnFeP0.5Si0.5 and Mn1.4Fe0.6P0.3Si0.7 allows pointing out that
the magnetic properties of the (Mn,Fe)2(Si,P) series are markedly monitored by a gradual
substitution of Mn to Fe in the 3f (p) site. Conversely, the substitution of Si to P on the 2c and
1b positions reveals less effective in influencing the magnetic metal-metal couplings.
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Fe Mössbauer analysis of MnFeP0,5Si0,5 at different temperatures (T), with <B> - average
value of hyperfine field in Gaussian distribution assuming a Lorentzian line half-width of 0.15
mm/s, σ - half-width distribution , IS - isomer shift reference to metallic iron, QS - quadrupole
splitting, P - relative component.
Fe Mössbauer analysis of Mn1.4Fe0,6P0,3Si0,7 at different temperatures (T) with with <B> average value of hyperfine field in Gaussian distribution assuming a Lorentzian line halfwidth of 0.15 mm/s, σ - half-width distribution , IS - isomer shift reference to metallic iron,
QS - quadrupole splitting, P - relative component.
Fig. 2 Left: 57Fe Mössbauer transmission spectra of MnFeP0.5Si0.5 measured at different
temperature. Right: the corresponding hyperfine field distributions.
Fig. 3 Left: 57Fe Mössbauer transmission spectra of Mn1.4Fe0.6P0.3Si0.7 measured at different
temperature. Right: The corresponding hyperfine field distributions.