V. B. Filippov | Searcharxiv

arXiv2015

Suppression of Superconductivity in Lu$_x$Zr$_{1-x}$B$_{12}$ : Evidence of Static Magnetic Moments Induced by Non-Magnetic Impurities

Based on low temperature resistivity, heat capacity and magnetization investigations we show that the unusually strong suppression of superconductivity in Lu$_x$Zr$_{1-x}$B$_{12}$ BSC-type superconductors in the range $x$$<$0.08 is caused by the emergence of static spin polarization in the vicinity of non-magnetic lutetium impurities. The analysis of received results points to a formation of static magnetic moments with $μ_{eff}$$\approx$$3μ_B$ per Lu-ion. The size of these spin polarized nanodomains was estimated to be about 5 $Å$.

cond-mat.str-el↗

arXiv2014

Charge transport in Ho$_x$Lu$_{1-x}$B$_{12}$: Separating Positive and Negative Magnetoresistance in Metals with Magnetic Ions

The magnetoresistance (MR) $Δρ/ρ$ of cage-glass compound Ho$_x$Lu$_{1-x}$B$_{12}$ with various concentration of magnetic holmium ions ($x$$\leq$0.5) has been studied in detail concurrently with magnetization M(T) and Hall effect investigations on high quality single crystals at temperatures 1.9-120 K and in magnetic field up to 80 kOe. The undertaken analysis of $Δρ/ρ$ allows us to conclude that the large negative magnetoresistance (nMR) observed in vicinity of Neel temperature is caused by scattering of charge carriers on magnetic clusters of Ho$^{3+}$ ions, and that these nanosize regions with AF exchange inside may be considered as short range order AF domains. It was shown that the Yosida relation $-Δρ/ρ$$\sim$$M^2$ provides an adequate description of the nMR effect for the case of Langevin type behavior of magnetization. Moreover, a reduction of Ho-ion effective magnetic moments in the range 3-9$μ_B$ was found to develop both with temperature lowering and under the increase of holmium content. A phenomenological description of the large positive quadratic contribution $Δρ/ρ$$\sim$$μ_D^2 H^2$ which dominates in Ho$_x$Lu$_{1-x}$B$_{12}$ in the intermediate temperature range 20-120 K allows to estimate the drift mobility exponential changes $μ_D$$\sim$$T^{-a}$ with $a$=1.3-1.6 depending on Ho concentration. An even more comprehensive behavior of magnetoresistance has been found in the AF state of Ho$_x$Lu$_{1-x}$B$_{12}$ where an additional linear positive component was observed and attributed to charge carriers scattering on the spin density wave (SDW). High precision measurements of $Δρ/ρ=f(H,T)$ have allowed us also to reconstruct the magnetic H-T phase diagram of Ho$_{0.5}$Lu$_{0.5}$B$_{12}$ and to resolve its magnetic structure as a superposition of 4f (based on localized moments) and 5d (based on SDW) components.

cond-mat.str-el↗

arXiv2004

Tunneling and Magnetic Characteristics of Superconducting ZrB$_{12}$ Single Crystals

Bulk and surface properties of high-quality single crystals of zirconium dodecaboride have been studied in the temperature range from 4.5 K up to the superconducting transition temperature which is found to be nearly 6.06 K. Scanning tunnelling spectroscopy data, together with dc and ac magnetization measurements, are consistent with the conventional s-wave pairing scenario, whereas they disagree in estimates of the electron-phonon coupling strength. We explain the divergence, supposing a great difference between the surface and bulk superconducting characteristics of the compound. This assertion is supported by our findings of a non-linear magnetic response to an amplitude-modulated alternating magnetic field, testifying to the presence of surface superconductivity in the ZrB$_{12}$ samples at dc fields exceeding the thermodynamic critical field.

cond-mat.supr-con↗