The magnetic state of 1212-type ruthenocuprate in magnetocaloric and magnetoresistivity measurements of polycrystalline samples of RuSr2Gd1-xCexCu2O8 and Ru1-xSr2GdCu2O8
Abstract
The magnetic properties of superconducting Ru1-xSr2GdCu2O8 (x=0, 0.02) and non-superconducting RuSr2Gd1-xCexCu2O8 (x=0.07, 0.1) were investigated by means of magnetocaloric experiments with complementary magnetoresistivity and ac susceptibility measurements. The isothermal magnetocaloric coefficient MT(B) assumes positive values in a broad range of temperatures (20K<T<231 K) and magnetic fields (0<B<13 T), i.e. also in the magnetically ordered state (Tm=132 K for RuSr2GdCu2O8 and Tm=150 K for RuSr2Gd0.93Ce0.07Cu2O8), which indicates no gain in the system's magnetic entropy with increasing magnetic field. The maximum in the MT(B) dependence was observed for RuSr2GdCu2O8 in a temperature vicinity of Tm, which indicates a ferromagnetic character of the accessed magnetic correlations. No spontaneous ferromagnetic order was revealed as the MT assumes limiting zero values at zero magnetic field for the whole range of investigated temperatures. Temperature dependencies of the specific heat reveal the magnetic-field-induced positive temperature shift of the anomaly associated with the magnetic transition in the Ru spin system. The MT(B) dependencies and the magnetoresistivity data suggest that the magnetic system may be inhomogeneous.
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