Itinerant electron magnetism: NMR and magnetization studies in Y(Co \V Al V )

Abstract The YCo system is characterized by a band structure which results in a magnetic instability of the itinerant subsystem. In such a case, the Co magnetism presents metamagnetic transitions upon application of an external magnetic "eld in the megagauss range. In the present paper we investigate the e!ect of substituting Co by Al in YCo . Polycrystalline samples of Y(Co \V Al V ) (x"0.00, 0.03, 0.05, 0.07 and 0.10), in the Co-rich site were investigated by means of magnetization M(H), AC susceptibility ! (T ) and nuclear magnetic resonance (NMR). The spontaneous magnetization as a function of Al concentration presents an anomalous behavior, which is closely related to N(E $ ,x), passing through a maximum at x"0.05, followed by a sharp decrease up to x"0.10. We show that the system becomes a very weak itinerant ferromagnet (VWIF) at x"0.10. NMR results show change in the Co hyper"ne "eld value upon Al alloying, which is related to changes in the conduction electrons density. An increase in the number of lines, with respect to YCo , attributed to the Al nucleus, was also veri"ed. 2001 Elsevier Science B.V. All rights reserved. Keywords: Itinerant electrons; Metamagnetism; Intermetallic compounds; NMR; Spin echo and relaxation; Susceptibility; Magnetization The YCo compound has been studied as a typical itinerant electron metamagnet. The Co magnetic instability is the origin of the two successive metamagnetic transitions (60 and 82 T) observed in the YCo magnetization curve under ultrahigh magnetic "elds. At the "rst transition, the ground state of the Co subsystem goes from a low magnetic state (LMS), to an intermediate one (IMS), and then, at the second transition, to a strong magnetic state (SMS) The purpose of the present work is to investigate the itinerant electron magnetism in Y(Co \V Al V ) compounds by means of AC susceptibility ! (T ), magnetization M(H) and nuclear magnetic resonance (NMR)