ELSEVIER Physica C 254 (1995) 124-130 PHYSICA Magnetization studies on ErNi2B2C single crystals R. Szymczak a,*, M. Baran a, L. Gtadczuk a, H. Szymczak a, Z. Drzazga b, A. Winiarska b a Institute of Physics, Polish Academy of Sciences, al. Lotnik6w 32/46, 02-668 Warsaw, Poland b Institute of Physics, Silezian University, Katowice, Poland Received 21 March 1995; revised manuscript received 28 June 1995 Abstract The magnetization of single crystal ErNi2B2C has been measured in the temperature range from 2 K up to 200 K and in magnetic fields up to 5 T. Performed measurements reveal a striking anisotropy both in paramagnetic and ordered states. It has been suggested that the high susceptibility near the N6el temperature is responsible for anomalies observed in the temperature dependence of the first field for flux penetration and for the irreversibility field. A cascade of metamagnetic transitions has been observed for an external field applied perpendicular to the c-axis. These transitions are discussed in the framework of the incommensurate mean-field model. 1. Introduction The newly discovered [1-3] rare-earth quaternary nickel boron carbide systems are model materials to study the interplay between the competing effects of superconductivity and magnetism. In this respect, their properties are reminiscent of the rare-earth rhodium borides and ternary molybdenum chalco- genides (see Refs. [4] and [5], and references therein). Particularly, a pronounced dip structure in the upper critical-field temperature dependence Hc2(T) was observed both in some of the new rare-earth nickel boride carbides RENi2B2C [6-8] and in magnetic superconductors RERh4B 4 and REM06S 8 [4,5]. Such a dip was observed in RENi2B2C for RE = Ho and * Corresponding author. Er. Since the dip in the Hc2(T) curve indicates the presence of strong pairbreaking near the N6el tem- perature the magnetization studies seem to be impor- tant to understand the role of magnetic structure and magnetic interactions in this new family of supercon- ductors. The availability of relatively large single crystals [9] allows for studies of the anisotropy in borocarbides. Such studies have been performed al- ready for HoNi2B2C (see, for example, Refs. [7] and [10]), therefore it was decided to carry out detailed measurements of the magnetic and superconducting properties of ErNi2B2C single crystals. The magnetic structure of ErNi2B2C, as has been already established [11,12], is associated with spins of the Er atoms. They are ordered in a transversely polarized planar sinusoidal structure, propagating along the a- (or b-) axis in equal domains, with the Er moments parallel to the b- (or a-) axis, respec- tively. 0921-4534/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0921-4534(95)00546-3