Thermopower and electrical resistivity behavior near the martensitic transition in Gd5(SixGe1−x)4 magnetocaloric compounds

Abstract Recently, the Gd5(SixGe1−x)4 system exhibits fascinating physical properties, namely giant magnetocaloric, magnetoresistance and magnetostriction effects near a first-order (martensitic like; T = T S ) magneto-structural transition. We report the thermopower behavior S ( T ) between 10 and 300 K for compounds with x = 0 , 0.10 and 0.45, belonging to three distinct regions of the magnetic/structural phase diagram. Large thermopower changes are observed near T S for x = 0 .10 ( T S = 78 K ; AFM-Orthorhombic II/FM-Ortho.I) and for x = 0.45 ( T S = 242 K ; PM-Monoc/FM-Ortho.I) with a Gaussian distribution in d S / d T , characteristic of a first-order phase transition. Near the purely magnetic transitions (PM/AFM) for x = 0 ( T N = 122 K ) and x = 0.10 ( T N = 127 K ) we observe d S / d T peaks governed by spin fluctuation effects. A comparative analysis between d S / d T and the resistivity derivative d ρ / d T near T S is made. At low temperatures S ( T ) behaves similarly in the ferromagnetic x = 0.10 and 0.45 compounds ( S ≈ AT + B T 2 ) , the anomalous B term being related to the mean internal field (spin wave excitations). For x = 0 (AFM phase at low T) one has S = AT (no B term; zero mean internal field).