ANISOTROPIC MAGNETORESISTANCE OF SINGLE-CRYSTAL HONI2B2C AND THE INTERPLAY OF MAGNETIC AND SUPERCONDUCTING ORDER

The in-plane resistivity and magnetization measurements as a function of the magnitude and direction of the magnetic field and the temperatu re are reported for single-crystal samples of the HoNi2B2C magnetic su perconductor. Features corresponding to several distinct magnetic phas es and the coexistence of superconductivity with two of the magnetic p hases are observed. Contrary to previous measurements for polycrystall ine samples, reentrant superconductivity is not observed in the absenc e of a field for these samples. The measurements indicate an extremely rich interplay between superconductivity and different magnetic struc tures that can be influenced by field, temperature, and current. The r esults correlate quantitatively with and complement previous determina tions of the magnetic phase diagram and qualitatively with determinati ons of the superconducting phases by measurements of the single-crysta l magnetization and heat capacity. HoNi2B2C is highly anisotropic, and phase diagrams for the field along the (100) and (001) directions are presented.