Magnetic phase transitions and entropy change in layered NdMn1.7Cr0.3Si2

A giant magnetocaloric effect has been observed around the Curie temperature, TC ∼ 42 K, in NdMn1.7Cr0.3Si2 with no discernible thermal and magnetic hysteresis losses. Below 400 K, threemagnetic phase transitions take place around 380 K, 320 K and 42 K. Detailed high resolution synchrotron and neutron powder diffraction (10–400 K) confirmed the magnetic transitions and phases as follows: TN intra ∼ 380 K denotes the transition from paramagnetism to intralayerantiferromagnetism (AFl), TN inter ∼ 320 K represents the transition from the AFl structure to the canted antiferromagnetic spin structure (AFmc), while TC ∼ 42 K denotes the first order magnetictransition from AFmc to canted ferromagnetism (Fmc + F(Nd)) due to ordering of the Mn and Nd sub-lattices. The maximum values of the magnetic entropy change and the adiabatic temperature change, around TC for a field change of 5 T are evaluated to be −ΔSM max ∼ 15.9 J kg−1 K−1 and ΔTad max ∼ 5 K, respectively. The first order magnetic transition associated with the low levels ofhysteresis losses (thermal <∼0.8 K; magnetic field <∼0.1 T) in NdMn1.7Cr0.3Si2 offers potential as a candidate for magnetic refrigerator applications in the temperature region below 45 K. SOME OF THE SCIENTIFIC SYMBOLS CAN NOT BE REPRESENTED CORRECTLY IN THE ABSTRACT. PLEASE READ WITH CAUTION AND REFER TO THE ORIGINAL ARTICLE

Ti substitution for Mn in MnCoGe - the magnetism of Mn0.9Ti 0.1CoGe

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 ΔSM max = 6.6J kg1 K 1 around Tstr ∼ 178 K, and ΔSM max = 4.2 J kg1 K1 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 ΔSM max can be expressed as ΔSMmax ∝ Bn with n = 1 for the structural transition around T str and n = 2/3 for the ferromagnetic transition around TC thereby confirming the second order nature of this latter transition