A comparative study of magnetic behaviours in bulk and ribbon samples of PrMn 2 Ge 2 compound

The magnetic properties of PrMn 2 Ge 2 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 K 0 = 42.0 GPa and its first derivative K 0 ' = 18.7 have been derived from the pressure -volume data. The Curie temperature from the intralayer antiferromagnetism ( AFl ) of PrMn 2 Ge 2 to a canted spin structure ( Fmc ) is T Cinter = 332 K for the bulk sample, decreasing to T Cinter = 320 K for the ribbon sample. The critical components gamma, beta and delta of this second order magnetic transition as determined from Kouvel-Fisher analyses, indicate long range magnetic interactions around T C inter . Based on these critical exponents the magnetization, field and ( H temperature data around T Cinter collapse onto two curves obeying the single scaling equation M ( H , epsilon ) = epsilon beta f +/- ) . The Debye temperatures and the density of states at epsilon beta + gamma the Fermi level are theta D = 306 K and N ( E F ) = 3 .47 state /eV atom for the bulk sample and theta D = 320 K and ( E F ) = 2 .18 state /eV atom for the ribbon sample with the nuclear specific heat coefficient for bulk PrMn 2 Ge 2 derived from the splitting of the nuclear hyperfine levels as C N = 517 mJ mol - 1 K -1 . With a field change of Delta B = 5 T, the maximum values of the magnetic entropy changes - Delta S max in the region around T Cinter are - Delta S max = 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 PrMn 2 Ge 2 could be a promising candidate for magnetic refrigeration applications in the room temperature region.