L Journal of Alloys and Compounds 333 (2002) 1–3 www.elsevier.com / locate / jallcom X-ray photoelectron spectroscopy and magnetism of Gd Ni Al 3 8 a a, b b a * V. Pop , M. Coldea , M. Neumann , S. Chiuzbaian , D. Todoran a Babes-Bolyai University, Faculty of Physics, 3400 Cluj-Napoca, Romania b ¨ ¨ University of Osnabruck, Fachbereich Physik, 49069 Osnabruck, Germany Received 30 January 2001; accepted 13 February 2001 Abstract X-ray photoelectron spectroscopy (XPS), magnetization and magnetic susceptibility of Gd Ni Al are reported. Both valence band and 3 8 core level spectra were analyzed. Ni atoms have no magnetic moment because of charge transfer of Gd conduction electrons to the 3d band. This effect is mainly related with the 6s electrons of Gd. The filling of the Ni 3d band is revealed by the density of states at the Fermi level, the chemical shifts of Gd and Ni core levels and the value of the effective magnetic moment in the paramagnetic state. The compound Gd Ni Al exhibits a collinear ferromagnetic arrangement of Gd moments below the Curie temperature T 561 K. A negative 3 8 C 3d band polarization of 0.15 m / Ni is induced by the exchange interactions with the Gd spins.  2002 Elsevier Science B.V. All rights B reserved. Keywords: Transition metal alloys; Rare earth alloys; Photoelectron spectroscopy; Magnetic measurements 1. Introduction band by the conduction electrons contributed by gadolinium. The intermetallic compound Gd Ni Al crystallizes in The X-ray photoelectron spectroscopy has been proved 3 8 the hexagonal CeNi structure type with the lattice param- to be of central importance for understanding the magnetic 3 ˚ ˚ properties and the electronic structure of the rare-earth eters a 55.07 A and c 516.23 A [1]. The Ni–Ni distances transition metal compounds. in Gd Ni Al are very close to those in Ni metal. In the 3 8 By a partial replacement of Ni (11%) with Al in GdNi , series RNi (R5rare-earth) only the compound CeNi 3 3 3 i.e. GdNi Al ;Gd Ni Al, the compound undergoes a crystallizes in the hexagonal structure ( P6 / mmc space 2.66 0.33 3 8 3 ˚ change in the crystalline structure from rhombohedral to group), with the lattice parameters a 54.98 A and c 5 hex ˚ hexagonal, with a large variation in the c lattice parame- 16.54 A. All the other compounds crystallize in a rhom- ] ters. This leads to a modification of the Gd–Ni distances bohedral Be Nb structure type ( R3 m space group). The 3 and of the surroundings of Ni and Gd, which implicitly parent compound GdNi , with the lattice parameters a 5 3 ˚ ˚ cause a change in the band structure of the compound. 4.99 A and c 524.54 A [2], is ferrimagnetically ordered rh The aim of this paper is to study the magnetic properties below T 5116 K [3]. The spontaneous magnetization C of the new compound Gd Ni Al and the magnetic state of extrapolated to 0 K has the value 6.55 m , smaller than 3 8 B 31 the Ni 3d electrons in this compound by using magnetic that of the Gd ion (7 m ). The Ni atoms occupy B measurements and XPS. non-equivalent lattice sites, having different magnetic contributions. The mean nickel magnetic moments m 5 Ni 0.15 m in GdNi , smaller than in Ni metal (0.6 m ), are B 3 B antiparallel oriented to those of gadolinium. Above the 2. Experimental Curie point, the temperature dependence of the reciprocal susceptibility has a nonlinear variation [4]. This behavior The investigated compound Gd Ni Al was prepared by 3 8 may be correlated with the change of the electronic argon arc melting. The sample was melted repeatedly (four structure of Ni atoms, as a result of partial filling of the 3d times) in the same atmosphere to ensure homogeneity. The weight loss of the final sample was found to be ,1%. The purity of the starting materials was 99.9% for Gd and Ni *Corresponding author. E-mail address: mcoldea@phys.ubbcluj.ro (M. Coldea). and 99.99% for for Al. X-ray powder diffraction measure- 0925-8388 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388(01)01730-3