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 temperature are reported for single-crystal samples of the Ho${\mathrm{Ni}}_2$ ${\mathrm{B}}_2$C magnetic superconductor. Features corresponding to several distinct magnetic phases and the coexistence of superconductivity with two of the magnetic phases are observed. Contrary to previous measurements for polycrystalline samples, reentrant superconductivity is not observed in the absence of a field for these samples. The measurements indicate an extremely rich interplay between superconductivity and different magnetic structures that can be influenced by field, temperature, and current. The results correlate quantitatively with and complement previous determinations of the magnetic phase diagram and qualitatively with determinations of the superconducting phases by measurements of the single-crystal magnetization and heat capacity. Ho${\mathrm{Ni}}_2$ ${\mathrm{B}}_2$C is highly anisotropic, and phase diagrams for the field along the (100) and (001) directions are presented.