L.D. Woolf

A new family of ternary intermetallic superconducting/magnetic stannides

Abstract A new family of rare earth-rhodium-tin intermetallic compounds, with the representative formula (RE)Rh x Sn y , has been synthesized in single crystal form. The compounds containing the heavier rare earths are superconducting and those with the lighter rare earths are generally magnetic. The compound ErRh 1.1 Sn 3.6 exhibits reentrant superconductivity with T c = 0.97 K and T m = 0.57 K as determined from ac magnetic susceptibility measurements. The synthesis and X-ray characterization of the series are described and the results of electrical resistivity, upper critical magnetic field, magnetic susceptibility, specific heat and neutron scattering measurements on the Er compound are given.

Superconducting and normal state properties of ErRh4B4 and LuRh4B4

Detailed heat capacity measurements of the ternary compounds ErRh4B4 and LuRh4B4 have been performed between 0.5 and 36 K and in magnetic fields up to 4 kG, yielding new information on crystal field effects in these materials and on the influence of externally applied magnetic fields on the coupled superconducting-ferromagnetic reentrant transition in ErRh4B4. Static magnetic susceptibility data on LuRh4B4 are presented which allow qualitative conclusions to be drawn regarding the magnitude of exchange enhancement and orbital paramagnetic effects in the RERh4B4 compounds. The electrical resistivity of ErRh4B4 has also been determined between 4 K and room temperature.

Coexistence of superconductivity and antiferromagnetic order in SmRh4B4

Abstract The ternary rare earth compound SmRh4B4 has been studied by means of upper critical field, low temperature specific heat, and static magnetic susceptibility measurements. A lambda-type specific heat anomaly, a discontinuity in the slope of the upper critical field versus temperature curve, and a cusp-like feature in the magnetic susceptibility suggest that superconductivity and long-range antiferromagnetic order coexist in SmRh4B4 below 0.87 K. Machidas theory for antiferromagnetic superconductors provides a good description of the upper critical field data, while the magnetic susceptibility data can be represented as the sum of a Curie-Weiss term with microeff = 0.632 microB and θp = −1.93 K and a temperature independent Van Vleck contribution.

Possible observation of the coexistence of superconductivity and long-range magnetic order in NdRh4B4

Abstract The ternary rare earth compound NdRh 4 B 4 has been studied by means of critical field, low temperature heat capacity, and static magnetic susceptibility measurements. Features in the upper critical field and heat capacity data at 1.31 K and 0.89 K suggest the occurrence of long-range magnetic order in the superconducting state. The temperature dependence of the static magnetic susceptibility follows a Curie-Weiss law with an effective magnetic moment μ eff = 3.58 ± 0.05 μ B and a Curie-Weiss temperature θ p = −6.2 ± 1.0 K between 20 K and room temperature. However,, magnetization vs. applied magnetic field isotherms suggest the development of a ferromagnetic component in the Nd 3+ magnetization at low temperatures.

Interaction between superconductivity and magnetism in the pseudoternary system (Lu1−xHox)Rh4B4

Abstract The boundaries between the normal paramagnetic, superconducting and normal magnetically ordered phases in the tetragonal pseudoternary rare earth system (Lu 1− x Ho x )Rh 4 B 4 have been established by means of a.c. magnetic susceptibility measurements to temperatures as low as 0.07 K. The heat capacities of the ternary compounds LuRh 4 B 4 and HoRh 4 B 4 and the pseudoternary compound (Lu 0.5 Ho 0.5 Rh 4 B 4 have been measured from 0.5 K to 36 K. The static magnetic susceptibility and a.c. electrical resistance have been determined between about 1 K and room temperature for the ferromagnetic ternary compound HoRh 4 B 4 .

Ferromagnetism in the RERh4B4 compounds

The magnetic ordering temperatures of the primitive tetragonal rare earth (RE) rhodium boride compounds exhibit a peak at DyRh4B4, rather than GdRh4B4 as predicted from ordering via the indirect RKKY exchange interaction. This deviation is analyzed in terms of the depression of the superconducting transition temperature of LuRh4B4 by dilute amounts of RE impurity ions and the magnetic heat capacities of the RERh4B4 compounds for RE = Gd, Tb, Dy, and Ho. The strength of anisotropic crystalline electric field forces, as inferred from magnetic entropy considerations, may be the origin of the anomalous magnetic ordering temperatures. In addition, the depression of the superconducting transition temperatures of ErRh4B4 and TmRh4B4 from that of LuRh4B4 is shown to arise primarily from elastic exchange scattering of the conduction electrons by the magnetic RE ions.

Low-temperature magnetic properties of HoRh4B4

The low-temperature magnetic properties of HoRh4B4 have been studied by means of measurements of the magnetic susceptibility, magnetization, specific heat, thermal expansion, and magnetostriction. The ferromagnetic phase transition at TM= 6.7 K shows almost ideal S = 1/2 mean field behavior in the specific heat. Crystal field effects due to the splitting of the J = 8 Hunds rule ground state of the Ho3+ ions result in Schottky anomalies in the specific heat and the thermal expansion and are also revealed in the low-field magnetic susceptibility and the magnetostriction. Information on the ground state doublet of the 4f electrons has been obtained from the nuclear contribution to the specific heat below 1 K and the high-field magnetization below TM.

Observation of the coexistence of superconductivity and long-range magnetic order in TmRh4B4

The ac electrical resistance, heat capacity, static magnetic susceptibility, thermal conductivity, and linear thermal expansion coefficient have been measured for the superconducting ternary compound TmRh4B4. The results indicate that the Tm3+ magnetic moments order at about 0.4 K, while bulk superconductivity, which occurs at 9.8 K, persists to temperatures below 60 mK, which was the low-temperature limit of the apparatus. Various possibilities for the type of magnetic order are examined.

Coexistence of superconductivity and long-range antiferromagnetic order in Gd1.2Mo6Se8

Abstract Neutron diffraction experiments confirm that the ternary rare earth compound Gd1.2Mo6Se8 orders antiferromagnetically in the superconducting state at a Neel temperature TN=0.75 K.

Coexistence of superconductivity and long-range magnetic order in TmRh4B4

Abstract Electrical resistance, heat capacity, thermal conductivity and linear thermal expansion coefficient measurements on TmRh 4 B 4 indicate that superconductivity and long-range magnetic order coexist in this compound for temperatures less than 0.4 K.