The magnetic properties and magnetocaloric effect in Mn1-xNixCoGe
Australian Institute of Physics
MnCoGe-based compounds reveal promise for magnetic refrigeration and as such have been extensively investigated over the last decade . Refrigeration based on magnetic cooling via the magnetocaloric effect offers potential as an alternative to conventional gas-compression systems. MoCoGe-based compounds have two crystallographic structures: nominally low temperature TiNiSi-type orthorhombic structure (Pnma) and the high temperature Ni2In-type hexagonal structure (P63/mmc). When the structural transition temperature between these two structures is ‘tuned’ between the respective Curie temperatures of the phases (~345 K for the orthorhombic phase and ~275 K for the hexagonal phase ), a magneto-structural transition can be obtained. Such a transition allows a direct change from the ferromagnetic orthorhombic phase to the paramagnetic hexagonal phase . For a magneto-structural transition, the lattice and magnetic entropy changes occur simultaneously, thereby providing scope for observation of a large magnetocaloric effect . The crystallographic structures and magnetic properties of annealed Mn1-xNixCoGe (x = 0.02, 0.03, 0.04, 0.05, 0.06 and 0.07) have been investigated using variable temperature X-ray diffraction and neutron diffraction (T = 5 - 320 K) with neutron diffraction measurements carried out both with and without applied magnetic fields for Mn0.95Ni0.05CoGe (B = 0 - 8 T). Such experiments allow separation of the structural and magnetic contributions to the total entropy change at a magneto-structural transition . The magnetic entropy changes have been derived in the conventional way from a series of isothermal magnetisation experiments, e.g. –ΔSm ~8.8 J kg-1 K-1 for a magnetic field change of ΔB = 0 - 5 T in Mn0.95Ni0.05CoGe.
Cobalt compounds, Crystal structure, Entropy, Germanium, Magnetic refrigerators, Magneto-thermal effects, Manganese compounds, Nickel compounds, Thermodynamic properties
Ren, Q, Y., Hutchinson, W. D., Wang, J. L., Studer, A. J., & Campbell, S, J. (2015). The magnetic properties and magnetocaloric effect in Mn1-xNixCoGe. Paper presented at the 39th Annual Condensed Matter and Materials Meeting, Charles Sturt University, Wagga Wagga, NSW, 3 February 2015 - 6 February 2015, (pp. 83). Retrieved from: https://physics.org.au/wp-content/uploads/cmm/2015/Wagga2015_10_Handbook.pdf