Study of the Second-Order “Hidden” Phase Transition of the Monoclinic Phase in the Mixed Phase Region of ${\rm Gd}_{5}{({\rm Si}_{\rm x}{\rm Ge}_{1-{\rm x}})}_{4}$

Gd₅(Si_xGe_1-x)₄ exhibits a first order phase transition for the compositions 0 <; x <; 0.575 leading to a magnetic phase transition as well. It is not possible to measure the second order phase (magnetic) transition temperatures of the individual phases with direct measurements. This is because the first order phase transition occurs before the second order phase transition. With modified Arrott plots we have shown previously that it is possible to estimate the second order phase transition of the Gd₅Si₄ -type orthorhombic phase. In this paper we have estimated the second order phase transition temperature of the Gd₅Si₂Ge₂-type monoclinic phase using a single crystal sample of Gd₅Si_1.5Ge_2.5 (0.375) which falls in the mixed phase region of the sample.