Magnetic, magnetocaloric and neutron diffraction studies on TbNi5-xMx (M = Co and Fe) compounds

Research highlights: → Structural and magnetic properties have been studied in TbNi5, TbNi5-xCox and TbNi5-xFex compounds. The results show that the TC increases considerably with increase of Fe concentration, whereas the increase is nominal in the case of Co. The increase in the TC is attributed to the increase in TM-TM and R-TM exchange interactions which are quite negligible in the parent compound. In general, the neutron diffraction data corroborates the magnetization results. The analysis of the neutron diffraction data shows that both Ni and Co do not carry any significant moment in TbNi5-xCox compounds. On the contrary, the TM sublattice carries considerable moment in TbNi4Fe. These conclusions are in reasonable agreement with the theoretical calculations. The magnetocaloric properties of compounds under investigation have been studied in terms of isothermal magnetic entropy change and adiabatic temperature change. MCE value is small in the substituted compounds compared to that of the parent compound, but we observe broad peaks in MCE in the former. The broad peak is attributed to the local variations in exchange and anisotropy, which causes magnetic randomness below TC. In this respect, we find that there are similarities between Fe substituted RNi2 and the present compounds. The magnetic and magnetocaloric properties seem to be strongly correlated in these compounds. - Abstract: The effect of substitution of Co and Fe for Ni in TbNi5 on the structural, magnetic and magneto-thermal properties has been investigated. Considerable enhancement of Curie temperature is observed with Fe substitution, whereas the increase is nominal in the case of Co. Neutron diffraction measurements reveal the redistribution of moments and site preference of substitutional ions in Ni 2c and 3g sites. In TbNi4Fe, both Ni and Fe as well as Tb are found to carry moment while in the case of TbNi4Co, mainly Tb carries the moment. Magnetocaloric behavior has been investigated from the magnetization and the heat capacity measurements. The magnetic and magnetocaloric properties are found to be strongly correlated in these compounds.