OCCURRENCE AND COMPOSITION DEPENDENCE OF SUPERCONDUCTIVITY AND MAGNETISM IN HONI2B2C

The dependence of the superconducting and magnetic properties of the r e-entrant superconductor HoNi2B2C on phase composition was investigate d with X-ray powder diffractometry, AC susceptibility measurements at ambient and applied pressure, and resistivity measurements. The experi mental results based on over 40 polycrystalline samples show that this phase occurs with three different types of behaviour: pure supercondu ctivity, re-entrant behaviour and a non-superconducting state. Startin g from a pure superconducting state, with changing phase composition a nomalies develop around 5.5 K and 6 K in the AC susceptibility, follow ed by re-entrant superconductivity. The anomalies are attributed to th e manifestation of modulated magnetic states, which are destructive to superconductivity. The application of hydrostatic pressure results in a modification of these anomalies. Further composition change leads t o a complete loss of superconductivity. The influence of volume contra ction and substitution effects will be discussed.