Structural transitions and magnetocaloric properties of low-cost MnNiSi-based intermetallics

A series of Mn1-xNi1-xFe2xSi0.95Al0.05 MM'X-type compounds (with x = 0.28, 0.3, 0.32 and 0.35) were investi-gated for their potential as magnetocaloric materials. Structural and magnetic properties were studied by magnetometry, microscopy and X-ray diffraction. Double substitution of Fe in Mn and Ni sites allowed to tune martensitic transition temperatures between low temperature orthorhombic and high temperature hexagonal structures from 373 K in x = 0.28-183 K in x = 0.35 during cooling. Transition temperatures occur around room temperature for x = 0.30 (300 K for cooling transformation) and 0.32 (270 for heating transformation). Isothermal entropy changes of-8,-19 and-26 J/kg.K were calculated for field changes of mu 0H = 0-2, 0-5 and 0-7 T for x = 0.30. The values are comparable to those reported for MnNi(SiAl)-based compounds with single site substitutions (Mn and Ni) by Fe. Further analyses show that high magnetic fields are necessary to induce the magnetostructural transition in all studied compounds, which can be attributed to the presence of secondary phases and/or disorder at a local level.

Automated summary

A series of Mn1-xNi1-xFe2xSi0.95Al0.05 MM'X-type compounds were investigated as potential magnetocaloric materials. The martensitic transition temperatures of the compounds were adjusted by double substitution of Fe in Mn and Ni sites. The isothermal entropy changes were calculated and found to be comparable to those of similar MnNi(SiAl)-based compounds. High magnetic fields were found to be necessary for inducing the magnetostructural transition due to the presence of secondary phases and/or disorder.