Ti substitution for Mn in MnCoGe – The magnetism of Mn0.9Ti0.1CoGe

•We detected and confirmed two magnetic phase transitions at ∼178K and ∼280K.•Both structural entropy and magnetic entropy contribute to the entropy change around Tstr.•−ΔSMmax can be expressed as −ΔSMmax∝Bn with n=1 around Tstr and n=2/3 around TC. Bulk magnetization measurements (5–320K; 0–8T) rev...

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Bibliographic Details
Published in:Journal of alloys and compounds 2013-11, Vol.577, p.475-479
Main Authors: 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.
Format: Article
Language:English
Subjects:
Alloys
Condensed matter: electronic structure, electrical, magnetic, and optical properties
Condensed matter: structure, mechanical and thermal properties
Domain effects, magnetization curves, and hysteresis
Entropy
Exact sciences and technology
Ferromagnetism
Magnetic fields
Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.)
Magnetic phase transitions
Magnetic properties and materials
Magnetically ordered materials: other intrinsic properties
Magnetism
Magnetization
Magnetization curves, magnetization reversal, hysteresis, barkhausen and related effects
Magnetocaloric effect
Magnetocaloric effect, magnetic cooling
Manganese
Neutron diffraction
Neutron diffraction in structure determination
Physics
Structure of solids and liquids
crystallography
Structure of specific crystalline solids
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Summary:•We detected and confirmed two magnetic phase transitions at ∼178K and ∼280K.•Both structural entropy and magnetic entropy contribute to the entropy change around Tstr.•−ΔSMmax can be expressed as −ΔSMmax∝Bn with n=1 around Tstr and n=2/3 around TC. Bulk magnetization measurements (5–320K; 0–8T) reveal that below room temperature Mn0.9Ti0.1CoGe exhibits two magnetic phase transitions at ∼178K and ∼280K. Neutron diffraction measurements (3–350K) confirm that the transition at ∼178K 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 ∼280K originates from the transition from ferromagnetism to paramagnetism. The magnetocaloric behaviour of Mn0.9Ti0.1CoGe around Tstr∼178K and TC∼280K as determined via the magnetic field and temperature dependences of DC magnetisation are given by the maximum values of the magnetic entropy changes −ΔSMmax=6.6Jkg−1K−1 around Tstr∼178K, and −ΔSMmax=4.2Jkg−1K−1 around TC∼280K for a magnetic field change of ΔB=0–8T. 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∼280K 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 −ΔSMmax can be expressed as −ΔSMmax∝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.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2013.06.134