muSR and Magnetometry Study of the Type-I Superconductor BeAu

We present muon spin rotation and relaxation (muSR) measurements as well as demagnetising field corrected magnetisation measurements on polycrystalline samples of the noncentrosymmetric superconductor BeAu. From muSR measurements in a transverse field, we determine that BeAu is a type-I superconductor with Hc = 256 Oe, amending the previous understanding of the compound as a type-II superconductor. To account for demagnetising effects in magnetisation measurements, we produce an ellipsoidal sample, for which a demagnetisation factor can be calculated. After correcting for demagnetising effects, our magnetisation results are in agreement with our muSR measurements. Using both types of measurements we construct a phase diagram from T = 30 mK to Tc = 3.25 K. We then study the effect of hydrostatic pressure and find that 450 MPa decreases Tc by 34 mK, comparable to the change seen in type-I elemental superconductors Sn, In and Ta, suggesting BeAu is far from a quantum critical point accessible by the application of pressure.Comment: 10 pages, 8 figure

Doping induced quantum phase transition in the itinerant ferromagnet scandium indium

Examination of quantum critical points of itinerant electron systems will aid with understanding of d-electron magnetism that exhibits both local and itinerant characteristics in different families of compounds. Doping-induced quantum phase transition of the itinerant ferromagnet Sc 3.1 In that is composed of non-magnetic elements is the focus of our work. Polycrystalline samples of (Sc 1-x Lu x ) 3.1 In with 0≤ x≤ 0.08 were prepared by arcmelting and then annealing for an extended period of time. Susceptibility measurements were performed in an applied magnetic field H = 0.1 T for temperatures T = 1.85 K to 300 K. Linearity of Arrott plots in low-field region was significantly improved by implementing the non-mean-field Arrott-Noakes technique where plotting M 1/β vs. ( H/M ) 1/γ is used to determine both the Curie temperature and composition. Modified Arrott plot approach was used in order to determine the new critical exponents β, γ and δ that better describe this compound. The Curie temperature of the Sc 3.1 In compound was found to be T C = 4.4 K and the critical composition x c = 0.02. This work was supported by NSF DMR 0847681

Search, Discovery, Synthesis and Characterization of Itinerant Magnets Composed of Non-magnetic Constituents

The origin of magnetism in metals has been traditionally discussed in two diametrically opposite limits: itinerant and local. Itinerant magnetism, caused by conduction electrons, has been of interest due to intriguing phenomena that frequently accompany it: heavy fermion behavior, coexistence of superconductivity and magnetism, metamagnetic transitions, spin- and cluster-glass behavior, multisublattice magnetism, non-Fermi liquid behavior, and quantum criticality. Surprisingly, while many systems exhibit both local and itinerant magnetism, only two are known to contain no local moment ions: Sc3In and ZrZn2. Doping experiments on Sc3In were used to investigate the effects of both magnetic (Er) and non-magnetic (Lu) substitutions within the itinerant matrix. While the former induces a cluster-glass state, the latter drives the system through a quantum phase transition. A novel Arrott-Noakes scaling indicates that Sc3In cannot be described by the mean-field theory, contrary to what has been seen in ZrZn2. This indicates that ZrZn2 and Sc3In are drastically different, which is likely associated with the dimensionality of spin fluctuations. Given these disparities between two seemingly analogues systems, more itinerant compounds containing non-magnetic elements are needed. While the Stoner criterion for band ferromagnetism calls for high density of states at the Fermi level together with strong electron correlations, more conditions are likely at play. A systematic search among 3d systems resulted in the discovery of the first itinerant antiferromagnet composed of non-magnetic elements TiAu. The spin density wave antiferromagnetic ordering separates this compound from the previously reported ferromagnetic ones. Furthermore, perturbation of TiAu lattice with doping resulted in an antiferromagnetic quantum critical point, which can provide insights on the validity of the self-consistent renormalization theory of spin fluctuations in itinerant magnets

Probing the superconducting pairing of the La₄Be₃₃Pt₁₆ alloy via muon-spin spectroscopy

ISSN:0953-8984ISSN:1361-648

Synthesis and Properties of Cobalt Complexes with [B₁₁H₁₁]^4– Ligands

The unusually high oxidation state + IV of cobalt is stabilized by ligands based on [B11H11]4– in dark blue colored Cs4[Co(B11H10.11(OH)0.75)2]·4.56H2O, K4[Co(B11H9.19(OH)1.81)2]·2H2O, Cs8[Co{(B11H6)2(O)(O2BOH)4}]2·4H2O and K4[Co{(B11H6)2(O2BOH)5}]·7H2O. These compounds were obtained by reacting Co2+ salts with [B11H14]− under alkaline conditions. In the absence of oxygen, Co(+III) compounds such as the light brownish K4[Co(B11H11)(CN)3]·KCl·2.5H2O are formed. The title compounds were characterized by X-ray crystallography. Cs8[Co{(B11H6)2(O)(O2BOH)4}]2·4H2O and K4[Co(B11H11)(CN)3]·KCl·2.5H2O were also characterized using IR-, UV–vis and cyclovoltammetry. Magnetic measurements of Cs4[Co(B11H10.11(OH)0.75)2]·4.56H2O and ESR measurements of Cs8[Co{(B11H6)2(O)(O2BOH)4}]2·4H2O show that in these Co(+IV) low-spin d5 complexes the unpaired electron is on the dx2–y2, dxy (E2g) orbitals

Crystal Chemistry and Physics of UCd11

In the phase diagram U-Cd, only one compound has been identified so far─UCd11 (space group Pm3̅m). Since the discovery of this material, the physical properties of UCd11 have attracted a considerable amount of attention. In particular, its complex magnetic phase diagram─as a result of tuning with magnetic field or pressure─is not well-understood. From a chemical perspective, a range of lattice parameter values have been reported, suggesting a possibility of a considerable homogeneity range, i.e., UCd11-x. In this work, we perform a simultaneous study of crystallographic features coupled with measurements of physical properties. This work sheds light on the delicate relationship between the intrinsic crystal chemistry and magnetic properties of UCd11

Superconductivity of MoBe22 and WBe22 at ambient- and under applied-pressure conditions

MoBe22 and WBe22 compounds belong to the binary XBe22 (X = 4d or 5d metal) family of superconductors, whose critical temperature depends strongly on X. Despite the multiphase nature of these samples, it is possible to investigate the superconducting properties of MoBe22 and WBe22 at the macro- and microscopic level. A concurrent analysis by means of magnetization and heat-capacity measurements, as well as muon-spin spectroscopy (mu SR) was implemented. At ambient pressure, both compounds enter the superconducting state below 2.6 +/- 0.1 K (MoBe22) and 4.1 +/- 0.10 K (WBe22) and show modest upper critical fields [(mu H-0(c2)(0) = 48 +/- 1 mT and mu H-0(c2)(0) = 58 +/- 1 mT, respectively]. In WBe22, the temperature-dependent superfluid density suggests a fully gapped superconducting state, well-described by an s-wave model with a single energy gap. Heat-capacity data confirm that such a model applies to both compounds. Finally, ac magnetic susceptibility measurements under applied pressures up to 2.1 GPa reveal a linear suppression of the superconducting temperature, typical of conventional superconducting compounds.ISSN:2475-995

Crystal Chemistry and Physics of UCd₁₁

In the phase diagram U-Cd, only one compound has been identified so farUCd11 (space group Pm3̅m). Since the discovery of this material, the physical properties of UCd11 have attracted a considerable amount of attention. In particular, its complex magnetic phase diagramas a result of tuning with magnetic field or pressureis not well-understood. From a chemical perspective, a range of lattice parameter values have been reported, suggesting a possibility of a considerable homogeneity range, i.e., UCd11–x. In this work, we perform a simultaneous study of crystallographic features coupled with measurements of physical properties. This work sheds light on the delicate relationship between the intrinsic crystal chemistry and magnetic properties of UCd11