Strong magnetic pair breaking in Mn-substitutedMgB2single crystals

Abstract

Magnetic ions ͑Mn͒ were substituted in MgB 2 single crystals resulting in a strong pair-breaking effect. The superconducting transition temperature, T c , in Mg 1−x Mn x B 2 has been found to be rapidly suppressed at an initial rate of 10 K / % Mn, leading to a complete suppression of superconductivity at about 2% Mn substitution. This reflects the strong coupling between the conduction electrons and the 3d local moments, predominantly of magnetic character, since the nonmagnetic ion substitutions, e.g., with Al or C, suppress T c much less effectively ͑e.g., 0.5 K / % Al͒. The magnitude of the magnetic moment ͑Ӎ1.7 B per Mn͒, derived from normal state susceptibility measurements, uniquely identifies the Mn ions to be divalent, and to be in the low-spin state ͑S =1/2͒. This has been found also in x-ray absorption spectroscopy measurements. Isovalent Mn 2+ substitution for Mg 2+ mainly affects superconductivity through spin-flip scattering reducing T c rapidly and lowering the upper critical field anisotropy H c2 ab / H c2 c at T = 0 from 6 to 3.3 ͑x = 0.88% Mn͒, while leaving the initial slope dH c2 /dT near T c unchanged for both field orientations.

Spin-resolved spectra of Shiba multiplets from Mn impurities inMgB2

“…[15][16][17][18] It is therefore an interesting question how the presence of these two gaps influences the structure of Shiba states. Although a series of experimental 19,20 and theoretical 21,22 investigations have been recently completed for MgB 2 doped with nonmagnetic as well as magnetic impurities, no experimental or theoretical study has been completed for the local electronic structure of a single magnetic impurity in this compound. This paper now provides a detailed theoretical discussion of the single magnetic impurity problem in MgB 2 and other superconductors where the multiple degrees of freedom of the conduction electrons and the impurity could lead to experimentally observable consequences.…”

How the substitution of Zn for Cu destroys superconductivity in YBCO system?

“…Doping of the magnetic ions like Fe, Co and Ni in the YBCO at the Cu sites induces a magnetic moment and magnetic pair breaking [1]. Introducing the magnetic ion Mn at the Mg site in the MgB 2 also induces a local magnetic moment and the pair breaking effect [17]. Even in the YNi 2 B 2 C system wherein magnetism can coexist with superconductivity, when magnetic Ho ion is substituted at the Y site, the T c decreases [18].…”

Thermoelectric Power of MgB2Single Crystals Doped with Holes and Electrons

“…The applied temperature and pressure conditions for the growth of C substituted crystals were determined in our previous studies [3][4][5]. The successful method to obtain Li and C-Li substituted crystals was described in Ref.…”

“…The superconducting transition temperature, T c , upper critical field and its anisotropy, gaps width, intra-and interband scattering, defect structure, etc., can be tuned in the wide range if the doping with holes and electrons is possible. Introducing Li, Al, Mn, Fe, and C into the melt, one can grow MgB 2 crystals where Mg and B are partially substituted and thus the crystals are doped with holes (Li) and electrons (Al, Fe, C) or they are substituted isovalently (Mn) [1][2][3][4][5][6][7]. The substituted crystals can be used to study the influence of doping and/or intra-and interband scattering on the anisotropic normal and superconducting properties of MgB 2 .…”