The magnetic state of 1212-type ruthenocuprate in magnetocaloric and magnetoresistivity measurements of polycrystalline samples of RuSr2Gd1-xCexCu2O8 and Ru1-xSr2GdCu2O8

TL;DR

This study investigates the magnetic properties of ruthenocuprate samples using magnetocaloric, magnetoresistivity, and ac susceptibility measurements, revealing ferromagnetic correlations without spontaneous ferromagnetic order and suggesting magnetic inhomogeneity.

Contribution

It provides new insights into the magnetic state of 1212-type ruthenocuprates, combining multiple measurement techniques to characterize magnetic correlations and inhomogeneity.

Findings

Positive magnetocaloric coefficient indicates ferromagnetic correlations.

No spontaneous ferromagnetic order observed in samples.

Magnetic inhomogeneity suggested by data.

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 M_{T}(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 (T_{m}=132 K for RuSr2GdCu2O8 and T_{m}=150 K for RuSr2Gd0.93Ce0.07Cu2O8), which indicates no gain in the system's magnetic entropy with increasing magnetic field. The maximum in the M_{T}(B) dependence was observed for RuSr2GdCu2O8 in a temperature vicinity of T_{m}, which indicates a ferromagnetic character of the accessed magnetic correlations. No spontaneous ferromagnetic order was revealed as the M_{T} 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 M_{T}(B) dependencies and the magnetoresistivity data suggest that the magnetic system may be inhomogeneous.