Magnetic phase diagram of YNi₂B₂C

Abstract

Structurally, YNi₂B₂C is a layered material. However, measurements on a single crystal show no anisotropy in the magnetic response. Accordingly, we have determined the values of H_c1(T), H_r(T) and H_c2(T) (T_c = 15.45 K) through detailed magnetisation and resistivity measurements using a polycrystalline sample. The values of the intrinsic parameters H_c1(0), H_c2(0), H_c(0), λ_GL(0) ξ_GL(0), k₀ are estimated to be 220 Oe, 52 kOe, 1.8 kOe, 1630 Å, 80 Å and 20.4, respectively. The H_c1(T) data is found to conform to the quadratic relation H_c1(0)[1 - (T/T_c)²] for T < 14.4 K and above this temperature the fall is faster. The H_r(T) data fit to a power-law response, [1 - (T/T_c)]^1.6, and the H_c2(T) curve shows an unusual curvature, namely, a concave upward feature. Our sample is brittle and electron microscopy reveals that it could comprise weakly coupled grains. As a result, our sample exhibits intergranularity effects near T_c via the negative peak effect in field-cooled warm up data and asymmetry in the hysteresis loop recorded after trapping of flux. The deviation of H_c1(T) values from the quadratic behaviour near T_c and the concave upward feature in the H_c2 curve are viewed as the consequence of the presence of "weak links" as the temperature approaches T_c.