Magnetic and XPS studies on RNi5 (R=La, Nd, Tb, Dy)-based compounds

Magnetic measurements and XPS studies were performed on LaNi5-xAlx, TbNi5-xAlx, DyNi5-xAlx, LaNi5-xCux and NdNi5-xCux systems. In addition, band structure calculations were also performed. The nickel moments in RNi5 (R=Nd, Tb, Dy) compounds are of ≅ 0.17 μB and ≅ 0.25 μB at 2c and 3g sites, respectively. The nickel moments, in low temperature range, decrease when increasing Al or Cu content and are practically nil for x > 1. The 4f-5d-3d exchange interactions were analyzed and the contributions of local 4f-5d and short range 5d-3d exchange interactions to 5d band polarization are estimated. An effective field of the order of (30-40) T is necessary to induce a nickel moment, at 1.7 K. Above the Curie temperatures, the effective nickel moments were determined. The LaNi5-xCux and LaNi5-xAlx systems, show, at T ≤ 10 K, a T2 dependence of the magnetic susceptibilities, while above a characteristic temperature T*, a Curie-Weiss contribution was evidenced. The magnetic behaviour of nickel is analyzed in models, which take into account electron correlation effects in d bands. (authors)