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. Machida's 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. © 1979.

We report the temperature dependence of the magnetic susceptibility of single crystals of PrB4, GdB4, TbB4, HoB4 and TmB4, both parallel and perpendicular to the tetragonal c-axis. We also present low temperature resistance measurements on crytals of GdB4 through TmB4. Two magnetic phase transitions are found for TbB4, DyB4, HoB4 and TmB4. For the latter two compounds, the lower transitions appear to be first order. For HoB4, we have measured the low temperature specific heat. The lower transition in TbB4 and HoB4 is rapidly depressed upon dilution with YB4. © 1981.

The ternary rare earth compound NdRh4B4 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 μeff = 3.58 ± 0.05 μB and a Curie-Weiss temperature θp = -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 Nd3+ magnetization at low temperatures. © 1979.

Using neutron scattering techniques we have examined the magnetic transitions for compounds in the (Ho1-xErx)Rh4B4 pseudoternary system. We find a wide variety of behavior ranging from mean-field behavior for HoRh4B4 to complicated behavior with more than one type of ordering for Ho0.3Er0.7Rh4B4. Our results for the pseudoternary compounds are consistent with a model in which Ho orders along the c axis with nearly its free-ion moment, while ER orders in the basal plane, but with a moment reduced from the free-ion value. Ordering along the c axis results in the destruction of superconductivity in a sharp transition at the same temperature that a sharp spike appears in the heat capacity. Because Ho and Er have competing orthogonal magnetic anisotropies, pseudoternary compounds near the composition Ho0.3Er0.7Rh4B4 are near a multicritical point in the magnetic phase diagram. © 1982 The American Physical Society.

Analysis of neutron diffraction data on the compound (Ho0.6Er0.4)Rh4B4 indicates that the Curie temperature is depressed by about 0.2 K, due to the occurrence of superconductivity, in agreement with theoretical predictions. The temperature dependence of the specific heat in the vicinity of the first-order re-entrant superconducting-ferromagnetic transition was computed by means of a simple model from the temperature dependence of the spontaneous magnetization of the Ho ions and was found to be in good agreement with the experimental data. © 1982.

Small-angle neutron experiments show that near the transition from superconductor to ferromagnet in ErRh4B4 scattering peaks occur at a wave vector |q's|=0.06 -1. The temperature and wave-vector dependence suggest this signal is due to oscillatory magnetization fluctuations caused by the electromagnetic coupling of magnetic and superconducting order parameters. The ferromagnetic Bragg scattering shows a 5% hysteresis and transition-temperature-smearing effects which are also due to magnetic-superconducting interactions. © 1980 The American Physical Society.

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 Ho 0.25Er0.75Rh4B4 are near a multicritical point in the magnetic phase diagram.

Superconductivity and magnetism are two types of order that can take place in materials at low temperatures. When the magnetic order is ferromagnetic, a competition exists between magnetism and superconductivity. Neutron scattering has been used to measure the interaction of magnetism and superconductivity in a series of ternary rare-earth alloys. A wide range of behavior is found near the magnetic transition, including mean-field magnetic ordering, first-order transitions between magnetism and superconductivity, and co-existence of ferromagnetism and superconductivity with a sinusoidally-modulated magnetic phase. © 1983.