Suppression of superconductivity inLuxZr1−xB12: Evidence of static magnetic moments induced by nonmagnetic impurities

Abstract

Based on low temperature resistivity, heat capacity and magnetization investigations we show that the unusually strong suppression of superconductivity in LuxZr1−xB12 BSC-type superconductors in the range x<0.08 is caused by the emergence of static spin polarization in the vicinity of nonmagnetic lutetium impurities. The analysis of received results points to a formation of static magnetic moments with µ ef f ≈3µB per Lu-ion. The size of these spin polarized nanodomains was estimated to be about 5Å.

Superconductivity in LuxZr1-xB12 Dodecaborides with Cage-Glass Crystal Structure

“…For the first set of Lu x Zr 1−x B 12 crystals only a very small paramagnetic signal was detected (see, for example, Figs.2a and 2b). On the contrary, for other samples with a similar Lu concentration the magnetization demonstrates a rather strong increase above H c2 (see Fig.2c) which has been interpreted (see [7] for details) in terms of an emergence of magnetic moments embedded in the nonmagnetic matrix of Lu x Zr 1−x B 12 . It is worth noting that in our experimental study also attempts were undertaken to measure the field dependence of magnetization of Lu x Zr 1−x B 12 crystals with the help of a PPMS-9 system.…”

“…4. Temperature dependences of specific heat C(T, H0) for (a) nonmagnetic x = 0.04 and (b) magnetic x = 0.074 crystals of LuxZr1−xB12 (see also [7] for details).…”

“…To verify both the quality of the samples and the Lu content, x-ray diffraction, Laue backscattering patterns, and microanalysis techniques were used. For all Lu x Zr 1−x B 12 single crystals the Lu/Zr ratio was estimated using a scanning electron microscope equipped with an energy dispersion microprobe system (JEOL JXA-8200 EPMA), see also [7] for details.…”

“…However, in case of LuB 12 the superconducting transition temperature reduces dramatically (T c ≈ 0.4 K for LuB 12 [4][5][6]), and the origin of the large T c difference for these two compounds with similar conduction bands and crystalline structures is not yet clarified. In this connection the study of normal state characteristics of Lu x Zr 1−x B 12 solid solutions with x < 0.08 at low temperatures allowed to observe the formation of static nanosized magnetic moments with µ eff ≈ 6µ B per Lu 3+ ion ( 1 S 0 ground state, 4f 14 -configuration) in the vicinity of nonmagnetic lutetium impurities in the nonmagnetic Zr-rich matrix [7]. According to arguments presented in [7], the strong suppression of superconductivity in Lu x Zr 1−x B 12 compounds can be attributed to pair breaking arising in the vicinity of these nanosized lutetium magnetic domains.…”

“…In this connection the study of normal state characteristics of Lu x Zr 1−x B 12 solid solutions with x < 0.08 at low temperatures allowed to observe the formation of static nanosized magnetic moments with µ eff ≈ 6µ B per Lu 3+ ion ( 1 S 0 ground state, 4f 14 -configuration) in the vicinity of nonmagnetic lutetium impurities in the nonmagnetic Zr-rich matrix [7]. According to arguments presented in [7], the strong suppression of superconductivity in Lu x Zr 1−x B 12 compounds can be attributed to pair breaking arising in the vicinity of these nanosized lutetium magnetic domains. In order to shed more light on the nature of the T c variation in these dodecaborides it looks promising to investigate the normal * corresponding author; e-mail: azarevich@lt.gpi.ru and superconducting states' parameters of Lu x Zr 1−x B 12 solid solutions in a wide range of Lu content (0 ≤ x ≤ 1).…”