H.C. Hamaker

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.

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 .

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.

Persistence of superconductivity in magnetically ordered SmRh4B4

Abstract Measurements of the thermal conductivity and the electrical resistivity between 50 mK and 4 K in zero magnetic field and in fields exceeding the superconducting critical field H c2 indicate the persistance of bulk superconductivity in magnetically ordered SmRh 4 B 4 .

Neutron diffraction study of Ho(Rh0.3Ir0.7)4B4

Abstract Using powder neutron diffraction techniques, we have examined the magnetic order of the pseudoternary compound Ho(Rh0.3Ir0.7)4B4 below the Neel temperature TN=2.7K. The magnetic structure consists of stacked antiferromagnetic basal plane sheets forming a body centered tetragonal unit cell, with a sublattice magnetization corresponding to 9.6±0.6μB per Ho3+ion at 1.5 K. Magnetic intensity versus temperature measurements indicate that the transition is second order and reveal no anomalous effects when the compound becomes superconducting at Tc=1.34K.

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.

Low-temperature heat capacity and ac magnetic susceptivility of the re-entrant ferromagnetic superconductor Ho1.2Mo6S8

Abstract Thermal hysteresis in the ac magnetic susceptibility and a spike-shaped anomaly in the heat capacity, superimposed on a feature due to ferromagnetic ordering, have been observed at the coupled superconducting to normal-ferromagnetic transition in Ho1.2Mo6S8.

Superconductivity and magnetism in the Ho1−xErxRh4B4 alloy system

We have used neutron scattering techniques to examine the magnetic transitions in the Ho1−xErxRh4B4 pseudoternary system. A wide variety of behavior is found, ranging from mean‐field behavior for HoRh4B4 to complicated behavior for ErRh4B4, where superconductivity and long‐range ferromagnetic order coexist between 0.7 and 1.2 K. Long‐range ferromagnetic order is found at the lowest temperatures for all alloy compositions. Alloys with more than about 30% Ho order magnetically along the c axis and superconductivity is destroyed in these alloys in a sharp transition coincident with magnetic ordering. Alloys near the ErRh4B4 composition order in the basal plane but undergo a complex ordering process through a sinusoidally modulated state. Because Ho and Er have competing orthogonal magnetic anisotropies, compounds near the composition Ho0.25Er0.75Rh4B4 are near a multicritical point in the magnetic phase diagram.