# Effect of Carbon Doping on the Structure and Magnetic Phase Transition in (Mn,Fe2(P,Si))

JOM, Jun 2017

Given the potential applications of (Mn,Fe2(P,Si))-based materials for room-temperature magnetic refrigeration, several research groups have carried out fundamental studies aimed at understanding the role of the magneto-elastic coupling in the first-order magnetic transition and further optimizing this system. Inspired by the beneficial effect of the addition of boron on the magnetocaloric effect of (Mn,Fe2(P,Si))-based materials, we have investigated the effect of carbon (C) addition on the structural properties and the magnetic phase transition of $\hbox {Mn}_{1.25}\hbox {Fe}_{0.70}\hbox {P}_{0.50}\hbox {Si}_{0.50}\hbox {C}_z$ and $\hbox {Mn}_{1.25}\hbox {Fe}_{0.70}\hbox {P}_{0.55}\hbox {Si}_{0.45}\hbox {C}_z$ compounds by x-ray diffraction, neutron diffraction and magnetic measurements in order to find an additional control parameter to further optimize the performance of these materials. All samples crystallize in the hexagonal $\hbox {Fe}_2\hbox {P}$-type structure (space group P-62m), suggesting that C doping does not affect the phase formation. It is found that the Curie temperature increases, while the thermal hysteresis and the isothermal magnetic entropy change decrease by adding carbon. Room-temperature neutron diffraction experiments on $\hbox {Mn}_{1.25}\hbox {Fe}_{0.70}\hbox {P}_{0.55}\hbox {Si}_{0.45}\hbox {C}_z$ compounds reveal that the added C substitutes P/Si on the 2c site and/or occupies the 6k interstitial site of the hexagonal $\hbox {Fe}_2\hbox {P}$-type structure.

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N. V. Thang, H. Yibole, X. F. Miao, K. Goubitz, L. van Eijck, N. H. van Dijk, E. Brück. Effect of Carbon Doping on the Structure and Magnetic Phase Transition in (Mn,Fe2(P,Si)), JOM, 2017, 1432-1438, DOI: 10.1007/s11837-017-2400-0