Magnetization, vortex state and specific heat in the superconducting state of RuSr2GdCu2O8 |
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Authors: | T P Papageorgiou E Casini H F Braun T Herrmannsdörfer A D Bianchi J Wosnitza |
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Institution: | 1. Hochfeld-Magnetlabor Dresden (HLD), Forschungszentrum Rossendorf, 01314, Dresden, Germany 2. Physikalisches Institut, Universit?t Bayreuth, 95440, Bayreuth, Germany
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Abstract: | Based on field-cooled dc-magnetization measurements in a
SQUID magnetometer with carefully controlled magnetic-field
profiles, we present evidence that diamagnetism is missing in the
superconducting state (T < 50 K) of the (weakly) ferromagnetic
(TM ≈130 K) superconductor RuSr2GdCu2O8
(Ru1212). Nevertheless, taking into account the granular nature of
the samples investigated so far, this cannot be taken as evidence
for the lack of a Meissner state or bulk superconductivity. It is
shown that for low applied magnetic fields a vortex state most
probably involves the intergrain area (area between the grains)
rather than the individual grains (bulk Ru1212). Furthermore, the
wide superconducting transition of Ru1212 (Tc,onset = Tc
≈48 K, Ts(R = 0) = Ts = 32 K) realized in
resistance measurements in zero applied magnetic field can be
readily understood as the effect of resistive grain contacts and is
not necessarily related to the movement of spontaneously induced
vortices in bulk Ru1212, as it has been suggested previously. A
comparison of the low-temperature specific heat of
Sr2GdRuO6 (Sr2116), the precursor for the preparation of
Ru1212 and thus a possible impurity phase, with previously reported
data for Ru1212 shows that it is unlikely that Sr2116 is responsible
for the specific-heat features attributed to the superconductivity
of Ru1212 and supports the existence of a bulk superconducting state
in the latter compound. |
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Keywords: | 74 72 -h Cuprate superconductors (high-Tc and insulating parent compounds) 74 25 Ha Magnetic properties 75 50 -y Studies of specific magnetic materials |
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