Magnetic properties of the ordered VPt3 alloy. - II. — Critical behaviour around the Curie point

Abstract

The ferromagnetic properties of the ordered VPt 3 alloy have been systematically investigated in a previous paper (Paper I). These investigations were carried out on bulk VPt 3 samples, one ordered in the Cu 3 Au structure (the VPt 3 (1) sample) and the other ordered in the TiAl 3 structure (the VPt 3 (2) sample); disordered (Cu like) VPt 3 is only paramagnetic. In the present paper, we report a detailed investigation on the critical properties of VPt 3 (1) and (2) around their respective Curie points (240 K and 210 K). The corresponding magnetization measurements were performed in the moderate field range 0.5 kOe≤H≤20 kOe, at several temperatures ranging from 195 K to 271 K for VPt 3 (1) and from 188 K to 235 K for VPt 3 (2). The iterative method used for the determination of T e , β, γ and δ is described in detail. We found T e =240.0 K, β=0.50, γ=1.19 and δ=3.38 for VPt 3 (1), against T c =210.3 K, β=0.51, γ=1.21 and δ=3.38 for VPt 3 (2). The critical properties of both VPt 3 samples are well described in the frame of the static scaling theory: Widom's scaling law γ=β(δ−1) is well satisfied and the critical DHW (Domb, Hunter, Widom) equation of state holds for VPt 3 (1) and (2). All results obtained here (critical exponents and amplitudes, critical magnetic equation of state), are discussed and compared with theory. We compare the critical magnetic equation of state of VPt 3 (1) and (2) with that of the most appro Etude detaillee du comportement critique des phases paramagnetique desordonnee (type Cu) et ferromagnetique ordonnee (type TiAl 3 ) de l'alliage VPt 3 autour des points de Curie respectifs (240 K, 210 K). Mesures d'aimantation et determination de la temperature critique et des exposants critiques. La loi d'echelle est verifiee. La transition magnetique est bien representee par l'equation critique d'etat magnetique. Comparaison aux modeles theoriques. Un modele d'interactions a longue portee convient pour les deux phases