Neutron-scattering studies on CeM2Ge2(M=Ag, Au, and Ru)

Abstract

The results of elastic, quasielastic, and inelastic neutron-scattering studies on polycrystalline CeM2Ge2 (M=Ag, Au, and Ru) are presented. All compounds reveal long-range magnetic order at low temperatures. Ferromagnetic (M=Ru), antiferromagnetic (M=Au), and incommensurate (M=Ag) structures were detected. Using time-of-flight (TOF) techniques, the crystalline electric-field splittings were determined. With high-resolution TOF experiments the temperature and wave-vector dependence of the magnetic relaxation rate was studied. Korringa-like behavior was found for the Au and Ru compounds.In CeAgzGe2 the temperature dependence of the magnetic relaxation rate exhibits a square-root dependence at high temperatures and shows a residual linewidth for low T. This behavior can be explained by strong hybridization effects of the f electrons with the delocalized band states which are active in heavy fermion systems. Previous results in CeCu2Ge2 and CeNi&Ge& are included, whenever necessary. Detailed comparison is made with results obtained in the disilicides.

Multiple magnetic structures of correlated Ce ions in intermetallic CeAu2Ge2

“…The magnetic susceptibility of CeAu 2 Ge 2 exhibits strong anisotropy with an easy [001] direction perpendicular to the tetragonal plane. 16,17 Previous measurements on a powder of CeAu 2 Ge 2 showed that the correlated Ce-ions develop a long range antiferromagnetic order below T N 16 K. 13 In this article, we report elastic neutron scattering measurements on a high quality single crystal sample of CeAu 2 Ge 2 . The crystals were synthesized by high temperature solution growth method using Bi flux and the quality was verified using X-ray measurements.…”

“…19,20 Previous as well as recent work on both polycrystalline and single crystal samples suggest that the crystal field level scheme in CeAu 2 Ge 2 consists of three doublets at ∆ 0 = 0 K, ∆ 1 12 meV and ∆ 2 18 meV. 13,16 The ground state is almost pure J z = ±5/2 with an admixture of ±3/2. The first excited doublet state is high enough in energy to avoid any significant intermixing between the ground and first excited state doublets, so that any induced moment magnetic state is highly unlikely.…”

“…13,16,17 However, as the sample is cooled below 10 K new magentic peaks start appearing with different temperature dependencies. As shown in the series of plots in Fig.…”

“…13 The present single-crystal Intensity (counts/46 sec) measurements allow for a much more detailed examination of the intensities and magnetic scattering pattern, which reveal qualitatively new features. In Fig.…”

“…[13][14][15] Since CeAu 2 Ge 2 , which is the weakest heavy fermion metal of the CeX 2 Ge 2 series, 13 belongs to the same noble metal group of elements (X = Cu, Ag, Au)-a natural corollary is expected but has never been observed. The magnetic susceptibility of CeAu 2 Ge 2 exhibits strong anisotropy with an easy [001] direction perpendicular to the tetragonal plane.…”