Nonsuperconductivity and magnetic features of the intermetallic borocarbide HoCo2B2C

摘要

Intrigued by the exotic features of the low-temperature superconducting and magnetic phase diagram of HoNi2B2C, this work searched for similar features in the isomorphous HoCo2B2C [LuNi2B2C-type structure, a = 3.500(3) Angstrom, c = 10.590(9) Angstrom]. In contrast to the former, no superconductivity is observed down to 30 mK, indicative of a relative lattice stiffening and a reduction in N(E-F). The magnetic ordering of the Ho sublattice sets in at T-N = 5.4(1) K (Co-sublattice carries no magnetic moment). The magnetic entropy up to 10 K is suggestive of an electronic ground-state doublet. No field-induced cascade of magnetic phase transitions was observed in the range 1.8 K < T < T-N, however, zero-field specific heat revealed two peaks, centered at T-1 = 1.46(6) K and T-2 = 0.31(2) K. The T, peak, not evident in ac susceptibility (chi(ac)), is conclusively associated with the Ho3+ nuclear Schottky-type contribution: the derived hyperfine parameters are comparable to that of those of HoNi2B2C and Ho metal. The T-1 event, evident also in chi(ac)(T), is probably a manifestation of an order-to-order magnetic phase transition. [S0163-1829(99)03126-4]. [References: 45]