Structure and Magnetic Properties of CeIr₃B_2−xSi_x System

Abstract

The compound CeIr₃B₂ crystallizes in a monoclinic unit cell (space group C2/m) with a structure related to that of hexagonal CeCo₃B₂ [1]. Cerium has been shown to be in a mixed valent states in this compound [2]. On the other hand CeRh₃B₂ has the hexagonal CeCo₃B₂ type structure (space group P6/mmm) and orders ferromagnetically with T_C=115K, and a small magnetic moment of 0.42 μ_B/fu. The magnetism in CeRh₃B₂ [3] is very puzzeling. To understand the origin of magnetism in CeRh₃B₂, many mixed alloys have been studied, such as (Ce_1−xLa_x)Rh₃B₂ [4], CeRh_3−xM_xB₂ (M= Ru,Os and Ir) [5−8] and CeRh₃B₂__xSi_x [9]. In this structure, hybridization of the Ce-4f electrons with neighbouring atoms is believed to play an important role [10]. Since Rh and Ir are isoelectronic and Ce-Ce distances are nearly the same in CeT₃B₂ (T = Rh and Ir), the absence of magnetic ordering in CeIr₃B₂ is rather surprising. We report on the structure and the magnetic behaviour of CeIr₃B_2−xSi_x alloys. We find that initial replacement of Si by B causes magnetic ordering to appear in this system.