The M5XB2 materials system has been widely studied as permanent magnetic materials[1] [2]. As permanent magnetic materials, their coercivity and magnetic energy product are lower than those of the mainstream permanent magnetic materials. Xie et al.[3] and Cedervall et al.[4] proposed that the Mn5PB2 and (Fe1-xCox)5PB2 compounds have the prospect of being applied as magnetocaloric materials due to their near room temperature Curie temperature. In this work, the structure and magnetocaloric properties of the Mn5(SiP)B2 compounds of the M5XB2 material system were studied. According to a refinement of the XRD data the Mn5(Si1-xPx)B2 compounds all crystallize in the Cr5B3–type body-centered tetragonal structure, with a small amount of Mn2P as a secondary phase (less than 7%). The lattice parameters and the unit-cell volume of the compounds change linearly with the increase in P content. These experimental results are consistent with calculated DFT results. The Curie temperature of the compounds can continuously be adjusted between 305 and 411 K by changing the Si/P ratio. The introduction of P also caused a decrease in saturation magnetization. The magnetic phase transition of these compounds was determined using Arrot plots and the field exponent n for the magnetic entropy change based on Landau's theory. The studied compounds all show a second-order magnetic phase transition. Since the compounds show a second-order phase transition, the magnetic entropy change caused by the phase transition was not large: 1.9 and 1.4 J/kgK for Mn5SiB2 and Mn5PB2, respectively. However, the advantage of this series of compounds is that the Curie temperature can be adjusted continuously around room temperature.

![](https://assets.underline.io/uploads/markdown_image/1/image/1d9940cac68d7c5951d382a4b1969178.jpg)

Fig. 1. Temperature dependence of magnetization of Mn5(Si1-xPx)B2(0 ≤ x ≤ 1) in a field of 0.01T.


![](https://assets.underline.io/uploads/markdown_image/1/image/a3a6abe7d32a72ba069affbbfed1f01d.jpg)

Fig. 2. TC as a function of P content for Mn5(Si1-xPx)B2 (0 ≤ x ≤ 1).

Magnetocaloric Properties of a New Type of Magnetocaloric Materials - M5XB2 System

Magnetic cooling, based on the magnetocaloric effect (MCE), offers many advantages over traditional compressor-based refrigeration. Among many promising materials, the (Mn,Fe)2(P,Si) family of compounds attracts broad attention due to the non-toxic composition, large magnetocaloric effect, tunable Curie Temperature (Tc) and limited thermal hysteresis (ΔThys). The stoichiometry of the quaternary alloy (Mn,Fe)2(P,Si) has a significant impact on the magnetocaloric performance. Additionally, the magnetocaloric response of the (Mn,Fe)x(P,Si) system is highly sensitive to the heat treatment conditions. For the Fe-rich (Mn,Fe)x(P,Si) (2.00 ≥ x ≥ 1.80) melt-spun ribbons, we investigated the phase purity as a function of starting composition and annealing temperature. For a first batch, annealed for 2h at 1373 K, we found with decreasing M/NM ratio from 2.00/1 to 1.90/1 an increase in Tc from 251.3 to 310.1 K and a decrease in ΔThys from 33.3 to 8.3 K. These changes were accompanied by a decreasing amount of the metal-rich (Mn,Fe)3Si impurity phase. A further decrease of the M/NM ratio leads to a rapid reduction of Tc to 178.5 K and an increase in hysteresis to 75.7 K. Along with these changes, the formation of the non-metal (Mn,Fe)Si impurity phase was observed. In order to investigate the effect of the heat treatment, ribbons were annealed at 1313 and 1433 K. The magnetic entropy change (ΔSm) and ΔThys increase with increasing annealing temperature, indicating the enhancement of the First Order Magnetic Transition (FOMT). The formation and composition of the (Mn,Fe)3Si impurity strongly depend on the annealing conditions, as evidenced by SEM/EDS analysis. The change in the annealing temperature caused a significant change in the composition and amount of the (Mn,Fe)3Si impurity phase. These changes were accompanied by the enlargement of grains and grain boundaries. The (Mn,Fe)Si impurity phase segregated in the form of micro-sized inclusions. Unlike (Mn,Fe)3Si, the (Mn,Fe)Si impurity appeared stable and remained strongly Fe and Si-rich for all annealing temperatures.

Improving the Magnetocaloric Response of Fe-rich (Mn,Fe)2(P,Si) Alloys

The interest in the magnetic cooling devices has led to an intensive search for suitable well-performing magnetocaloric materials over the last 25 years. However, to this date only a few material systems have been found to be suitable for commercial applications. Computational screening makes possible sieving through thousands of known compounds without the need to perform time-consuming measurements and therefore can play an important role in detecting novel magnetocaloric materials. To identify such systems of interest we selected several screening parameters using properties of various well-known MCE materials as a reference. Along with magnetic properties, other factors important for practical applications were taken into consideration including price, availability, and toxicity of candidate materials. Combining these criteria, we implemented an algorithm for the screening process as a set of automated computational tools. It relies on information readily available in the structural databases to perform detailed modelling via ab-initio calculations. Two computational databases (Aflowlib and Materials Project) and two experimental databases (COD and ICSD) are used as initial source of information totaling to 800k candidate compositions. As a main metric to predict the magnetocaloric performance we use the magneto-elastic response of the candidate. This is done by computing magnetic moment of the material across a range of deformations, both volumetric and uniaxial. This parameter shows good correlation with ΔSM measured in known magnetocaloric materials. A step-by-step application of initial screening parameters to sort out unsuitable materials before performing more computationally heavy assessments allows us to quickly process large number of candidates. This resulted in a shortlist of promising compounds to serve as a guide for experimental research. The flexibility of the computational toolset makes it possible to easily build in additional screening parameters to further adjust or refine the search process.

An Efficient Strategy for the Discovery of Novel Magnetocaloric Materials

**Session chairs:** Tino Gottschall, Helmholtz-Zentrum Dresden-Rossendorf and Jiazheng Hao, Institute of High Energy Physics



FOA - Magnetocalorics I

technical paper

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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2022 Joint MMM-INTERMAG

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

**Session chairs:** R. Nirmala, Indian Institute of Technology and Franziska Scheibel, Technische University Darmstadt



Ekkes Brück

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Magnetocaloric Properties of a New Type of Magnetocaloric Materials - M5XB2 System

Improving the Magnetocaloric Response of Fe-rich (Mn,Fe)2(P,Si) Alloys

An Efficient Strategy for the Discovery of Novel Magnetocaloric Materials

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