Magnetic resonance anisotropy in CeB6: an entangled state of the art

Abstract

Electron spin resonance (ESR) in strongly correlated metals is an exciting phenomenon, as strong spin fluctuations in this class of materials broaden extremely the absorption line below the detection limit. In this respect, ESR observation in CeB6 provides a unique chance to inspect Ce3+ magnetic state in the antiferroquadrupole (AFQ) phase. We apply the original high frequency (60 GHz) experimental technique to extract the temperature and angular dependences of g-factor, line width and oscillating magnetization. Experimental data show unambiguously that the modern ESR theory in the AFQ phase considering the Γ8 ground state of Ce3+ ion completely fails to predict both the g-factor magnitude and its angular dependence. Alignment of the external magnetic field along [100] axis induces a strong (more than twofold) broadening of ESR line width with respect to the other crystallographic directions and results also in the anomalous temperature dependences of the g-factor and oscillating magnetization. In this experimental geometry the latter parameter surprisingly exceeds total static magnetization by 20% at T* ~ 2.5 K. We argue that the unusual physical picture of ESR in CeB6 may be strongly affected by spin fluctuations and dynamic collective effects predominantly pronounced in [100] direction.

Theory of Electron Spin Resonance in Ferromagnetically Correlated Heavy Fermion Compounds

“…There is good agreement between theory and experiment at T = 2.65 K for a proper choice of parameters (in contrast to statements in Ref. [44]). Both the Γ 8 multiplet and AFQ order are crucial ingredients for the observability of an ESR signal in a cubic environment.…”

“…This fit is quite different from the one attempted in Ref. [44] and would change their conclusions. All data are taken in the AFQ phase II.…”

“…The angular dependence of the resonance at 60 GHz has recently be measured in Ref. [44]. Their data with error bars for 1.8 K (open circles) and 2.65 K (dark circles) are shown in Figure 4.…”

“…[44]) is shown in Figure 5. The solid straight line corresponds to a Korringa relaxation for a small interval at intermediate T. The figure clearly shows that 1/T rel does not have a Korringa-like T-dependence, but a more complicated one.…”

A novel method of ESR oscillating magnetization value determination in strongly correlated metals

“…Basically, the integrated intensity is defined by oscillating magnetization M 0 , which may be introduced in the same way as in [3,4]. The M 0 parameter defines magnitude of the ESR absorption, and in most cases it coincides with static magnetization M st (EuB 6 [3], YbRh 2 Si 2 [5]), but there are some materials (CeB 6 [4], [6]) that demonstrate a significant difference between the oscillating M 0 and total static magnetization M st measured by standard technique for studying of magnetization. The comparison of M 0 and M st may provide important information on different magnetic contributions or interactions within the system [6].…”