Determination of Phase Transition and Critical Behavior of the As-Cast GdGeSi-(X) Type Alloys (Where X = Ni,Nd and Pr)

The aim of the paper is to present a study of the magnetocaloric effect and the nature of phase transition in the Gd₈₀Ge₁₅Si₅ (S1), Gd₇₅Ge₁₅Si₅Ni₅ (S2), Gd₇₅Ge₁₅Si₅Pr₅ (S3) and Gd₇₅Ge₁₅Si₅Nd₅ (S4) alloys. The magnetic entropy changes determined for studied samples, under external magnetic field ~3T, were 11.91, 12.11, 5.08 and 4.71 J/(kg K) for S1, S2, S3 and S4, respectively. The values of refrigerant capacity (under ~3T) were 164, 140, 160 and 140 J/kg for S1, S2, S3 and S4, respectively. The first order phase transition was detected for samples S1 and S2, while specimens S3 and S4 manifested the second order phase transition at the Curie point (T_C). The analysis of temperature evolution of the exponent n (ΔS_M = C·(B_max)ⁿ) showed the validity of this method in detecting either the first or the second order phase transition and the structural transition. The analysis of critical behavior was carried out for samples S3 and S4. The critical exponents and precise T_C values were calculated. The ascertained critical exponents were used to determine the theoretical value of the exponent n, which corresponded well with experimental result.