The magnetic state of 1212-type ruthenocuprate in magnetocaloric and magnetoresistivity measurements of polycrystalline samples of RuSr₂Gd_1−xCe_xCu₂O₈and Ru_1−xSr₂GdCu₂O₈

Abstract

The magnetic properties of superconducting Ru 1-x Sr 2 GdCu 2 O 8 (x=0, 0.02) and non-superconducting RuSr 2 Gd 1-x Ce x Cu 2 O 8 (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 T ≤ B ≤ 13 T), i.e. also in the magnetically ordered state (T m = 132 K for RuSr 2 GdCu 2 O 8 and T m =150 K for RuSr 2 Gd 0.93 Ce 0.07 Cu 2 O 8 ) 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 RuSr 2 GdCu 2 O 8 in the 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. arXiv:0810.5588v3

The Superconducting and Magnetic States in RuSr2GdCu2O8, Based on the Magnetic, Transport and Magneto-Caloric Characteristics

“…These characteristics were more extensively discussed in [27] also for the observed anomalous field induced increase of conductivity in the temperature range directly preceding the superconducting transition -which we linked to complex response of the constrained dimensionality superconducting phase in presence of the field dependent compound's magnetism (see also Ref. [28]). Figure 3 presents the corresponding temperature dependences of the ac susceptibility measured at two small amplitudes of the ac field -1 Oe and 0.…”

“…In Ref. [22] we comment more extensively on the synthesis of the two samples with slightly altered nominal stoichiometry, RuSr 2 GdCu 2 O 8 and Ru 0.98 Sr 2 GdCu 2 O 8 , whose selected properties also are discussed here. The approach was to modify the nominal formula of one of the to be compared samples by introducing slight deficiency of Ru, and for assuring the same reaction conditions during their simultaneous synthesis, to end up with the materials which properties may be compared in investigation for results of probable modification of the phase.…”

Commentary on the superconducting and magnetic properties of the ruthenocuprates

“…On further lowering the temperature the sublattice of Gd 3+ moments orders antiferromagnetically at 2.5 K [11] much to resemble the RE magnetic order in REBa 2 Cu 3 O 7 compounds. Our recent measurements of magnetic field dependencies of the isothermal magnetocaloric coefficient for ceramic sample of RuSr 2 GdCu 2 O 8 (value of the coefficient is proportional to field driven changes of the magnetic entropy) signals the response of a complex magnetic system, and appears to involve the magnetic correlations present in spatially constrained range [12]. Such response may be referred to consequence of magnetic phase separation, which was proposed to remain inherent characteristic of the Ru-1212 ruthenocuprates [13].…”

“…Since the syntheses were conducted at high temperature close to the melting point for this phase, most affected may indeed become local regions characterised by increased Ru sublimation. Further remarks on involved synthesis process were presented in [12]. Observed slight and reproducible shift of the magnetic ordering temperature (T m ≈ 126 K vs. 132 K for × = 0.02 vs. × = 0, Ru 1-x Sr 2 GdCu 2 O 8 ) may well result in dilution of the Ru magnetic sublattice [48].…”

The characteristics of the superconducting and magnetic phases in the polycrystalline samples of ruthenocuprates of nominal compositions RuSr2GdCu2O8, Ru0.98Sr2GdCu2O8 and Ru0.5Sr2GdCu2.5O8-d

“…Several properties of these samples were discussed in the preceding articles [11,18] where we extensively comment on the compounds synthesis, report the magnetic field dependencies of the isothermal magnetocaloric coefficient, and comment on the magnetic field dependent specific heat and magnetoresistivity of the normal state. The higher superconducting T c (throughout this text the T c references to an intra-grain superconducting transition) of the sample B (Ru 0.98 Sr 2 GdCu 2 O 8 , T c on ≈ 50 K) comparing to A (T c on ≈ 40 K RuSr 2 GdCu 2 O 8 ) was ascribed to the effect of deficiency of Ru written into the nominal formula.…”