Magnetic phase diagram of YNi<SUB>2</SUB>B<SUB>2</SUB>C

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 Hc1(T), Hr(T) and Hc2(T) (Tc = 15.45 K) through detailed magnetisation and resistivity measurements using a polycrystalline sample. The values of the intrinsic parameters Hc1(0), Hc2(0), Hc(0), &#955;GL(0) &#958;GL(0), k0 are estimated to be 220 Oe, 52 kOe, 1.8 kOe, 1630 &#197;, 80 &#197; and 20.4, respectively. The Hc1(T) data is found to conform to the quadratic relation Hc1(0)[1 - (T/Tc)2] for T &lt; 14.4 K and above this temperature the fall is faster. The Hr(T) data fit to a power-law response, [1 - (T/Tc)]1.6, and the Hc2(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 Tc 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 Hc1(T) values from the quadratic behaviour near Tc and the concave upward feature in the Hc2 curve are viewed as the consequence of the presence of "weak links" as the temperature approaches Tc