Magnetoresistance and the field-induced magnetic phase transitions in the re-entrant superconductor HoNi2B2C

Magnetoresistivity isotherms of polycrystalline HoNi2B2C indicate, for T < T-N, a cascade of field-induced magnetic phase transitions. These transitions (and the recently reported H-T phase diagram) are interpreted as follows: an external field transforms, at H-c2, the superconducting antiferromagnetic ground state into a non-superconducting distorted helical state. On increasing the field further, such a distorted helical state is transformed into the ferromagnetic state via two types of fan-like spin structures. Furthermore, a discussion is given regarding the following characteristic low-T features of HoNi2B2C (i) the driving mechanism behind the formation of the helical state (ii) the spontaneous transformation of the helical state into the commensurate AFM state and (iii) the influence of the magnetic field and impurities on the helical state.