Ti substitution for Mn in MnCoGe - the magnetism of Mn0.9Ti0.1CoGe

Bulk magnetization measurements (5–320 K; 0–8 T) reveal that below room temperature Mn0.9Ti0.1CoGe exhibits two magnetic phase transitions at ∼178 K and ∼280 K. Neutron diffraction measurements (3–350 K) confirm that the transition at ∼178 K is due to the structural change from the low-temperature orthorhombic TiNiSi-type structure (space group Pnma) to the higher temperature hexagonal Ni2In-type structure (space group P63/mmc), while the transition at ∼280 K originates from the transition from ferromagnetism to paramagnetism. The magnetocaloric behaviour of Mn0.9Ti0.1CoGe around Tstr ∼ 178 K and TC ∼ 280 K as determined via the magnetic field and temperature dependences of DC magnetisation are given by the maximum values of the magnetic entropy changes −Δ S M max = 6.6 J kg−1 K−1 around Tstr ∼ 178 K, and −Δ S M max = 4.2 J kg−1 K−1 around TC ∼ 280 K for a magnetic field change of ΔB = 0–8 T. Both structural entropy – due to the unit cell expansion of ∼4.04% – and magnetic entropy – due to an increase in the magnetic moment of ∼31% – are found to contribute significantly to the total entropy change around Tstr. Critical analysis of the transition around TC ∼ 280 K leads to exponents similar to values derived from a mean field theory, consistent with long-range ferromagnetic interactions. It was found that the field dependence of −Δ S M max can be expressed as −Δ S M max ∝ Bn with n = 1 for the structural transition around Tstr and n = 2/3 for the ferromagnetic transition around TC, thereby confirming the second order nature of this latter transition.© 2013, Elsevier Ltd.

Keywords

Neutrons, Diffraction, Manganese, Cobalt, Germanium, Thallium

Citation

Wang, J. L., Shamba, P., Hutchison, W. D., Md Din, M. F., Debnath, J. C., Avdeev, M., Zeng, R., Kennedy, S. J., Campbell, S. J., & Dou, S. X.(2013). Ti substitution for Mn in MnCoGe - the magnetism of Mn0.9Ti0.1CoGe. Journal of Alloys and Compounds, 577, 475-479. doi:10.1016/j.jallcom.2013.06.134