A Comparative Study of Magnetic Behaviours in Bulk and Ribbon Samples of Prmn2ge2 Compound

Abstract

The magnetic properties of PrMn2Ge2 samples in both the as-cast bulk and melt-spun ribbon forms have been investigated in detail by a comprehensive set of x-ray and neutron powder diffraction, magnetic and heat capacity measurements and corresponding sets of data analyses. Thermal expansion measurements indicate the presence of magnetoelastic coupling effects around all transition temperatures in the bulk sample.  The bulk modulus K0 = 42.0 GPa and its first derivative K0′ =18.7 have been derived from the pressure-volume data. The Curie temperature from the intralayer antiferromagnetism (AFl) of PrMn2Ge2 to a canted spin structure (Fmc) is TCinter = 332 K for the bulk sample, decreasing to TCinter = 320 K for the ribbon sample. The critical components γ, β and δ of this second order magnetic transition as determined from Kouvel-Fisher analyses, indicate long range magnetic interactions around TCinter.  Based on these critical exponents the magnetization, field and temperature data around TCinter collapse onto two curves obeying the single scaling equation .  The Debye temperatures and the density of states at the Fermi level are and  for the bulk sample and and for the ribbon sample with the nuclear specific heat coefficient for bulk PrMn2Ge2 derived from the splitting of the nuclear hyperfine levels as CN = 571 mJ mol-1 K-1.  With a field change of DB= 5 T, the maximum values of the magnetic entropy changes -ΔSmax in the region around TCinter are -ΔSmax = 3.00 J/kg K and 2.35 J/kg K for the bulk and ribbon samples respectively, while the relative cooling power (RCP) for the ribbon-spun sample, RCP = 135.9 J/kg, is significantly higher than the value of RCP = 116.6 J/kg for the bulk sample.  These findings indicate that PrMn2Ge2 could be a promising candidate for magnetic refrigeration applications in the room temperature region.

Keywords: magnetic phase transition, x-ray diffraction, Magnetocaloric effect