A comparative study of magnetic behaviours in bulk and ribbon samples of PrMn2Ge2 compound

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 T_C^inter = 332 K for the bulk sample, decreasing to T_C^inter = 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 T_C^inter. Based on these critical exponents the magnetization, field and temperature data around T_C^inter collapse onto two curves obeying the single scaling equation $M\left(H,\epsilon \right)={\epsilon }^{\beta }{f}_{\pm }\left(\frac{H}{{\epsilon }^{\beta +\gamma }}\right)$. The Debye temperatures and the density of states at the Fermi level are ${\theta }_D=306K$ and $N\left(E_F\right)=3.47\text{state}/\text{eV}\text{atom}$ for the bulk sample and ${\theta }_D=320K$ and $\left(E_F\right)=2.18\text{state}/\text{eV}\text{atom}$ for the ribbon sample with the nuclear specific heat coefficient for bulk PrMn₂Ge₂ derived from the splitting of the nuclear hyperfine levels as C_N = 517 mJ mol⁻¹ K⁻¹. With a field change of ΔB = 5 T, the maximum values of the magnetic entropy changes -ΔS_max in the region around T_C^inter are -ΔS_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 PrMn₂Ge₂ could be a promising candidate for magnetic refrigeration applications in the room temperature region.