Magnetocaloric effect and magnetostructural coupling in Mn0.92Fe0.08CoGe compound

Abstract

The structural properties of Mn0.92Fe0.08CoGe have been investigated in detail using synchrotron x-ray diffraction in zero and applied pressure (p = 0–10 GPa). A ferromagnetic transition occurs around TC = 300 K and a large magnetic-entropy change −ΔSM = 17.3 J/kg K detected at TC for a field change of ΔB = 5 T. The field dependence of −ΔSMmax can be expressed as −ΔSMmax ∝ B. At ambient temperature and pressure, Mn0.92Fe0.08CoGe exhibits a co-existence of the orthorhombic TiNiSi-type structure (space group Pnma) and hexagonal Ni2In-type structure (space group P63/mmc). Application of external pressure drives a structure change from the orthorhombic TiNiSi-type structure to the hexagonal Ni2In-type structure. A large anomaly in heat capacity around TC is detected and the Debye temperature θD (=319(±10) K) has been derived from analyses of the low temperature heat capacity, T ≲ 10 K.

Magnetic and Structural Transitions Tuned through Valence Electron Concentration in Magnetocaloric Mn(Co1–xNix)Ge

“…57 In addition, strong magnetovolume effects are observed via changes in the lattice around the magnetic transition for the sample with x = 1.00 as shown in Figure 10. To estimate the spontaneous magnetostriction which causes the changes, the phonon contribution to the lattice thermal expansion was calculated using the Grüneisen-Debye model, 58,59 with a Debye temperature of 320 K 56 and extrapolated from the temperature region above T N . The fit to the Grüneisen-Debye model is shown as the dashed line in Figure 10.…”

“…Lattice parameters and unit-cell volume for MnNiGe sample ( T N = 360(5) K) determined from refinement of the neutron powder diffraction patterns. The dashed line on the unit-cell volume curve represents the phonon contribution to the thermal expansion (θ D = 320 K) …”

The magneto-structural transition in Mn1−xFexCoGe

“…Fe is a suitable and effective substitute for Mn to decrease the martensitic transformation temperature TM, as indicated by several papers [28][29][30][31][32][33]. Li et al [29] presented a magnetostructural transition and large MCE in Mn0.97Fe0.03CoGe (-ΔSM = 10.6 J kg -1 K -1 for a field change from 0 T to 5 T).…”

On the correct estimation of the magnetic entropy change across the magneto-structural transition from the Maxwell relation: Study of MnCoGeBx alloy ribbons

“…Among them, Gd 5 (Si x Ge 1-x ) 4 [1,16], La(Si,Fe,X) 13 (X= Co, Mn) [17,18], MnFe(P,X) with X = As, Ge, Si [6,19], non-stoichiometric NiMn-X-based Heusler-type (X= Ga, Sn, In, Sb) [20][21][22][23][24][25][26] or Mn(Co,Ni)Ge-based alloys [27][28][29][30][31][32][33][34][35][36][37]. It is worth noting that MnCoGe-based alloys have one of the largest contributions of S st to S T , giving rise to one of the highest reported GMCE in terms of the maximum value of S T [14].…”