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.
Highlights
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 YbRh2Si2 the estimate of the spin fluctuations contribution to the line width W gives W ~ 37 T, narrow electron spin resonance (ESR) was detected in this material with the help of X-band spectrometer at resonant field about 0.2 T1. This discrepancy stimulated an intense search for the physical mechanism, which might lead to narrowing of the ESR line width to observable values
This result is nothing but the second advent of well known Korringa mechanism of spin relaxation, where ESR line width is inversely proportional to magnetic susceptibility W ~ 1/χ5
Summary
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. Recent comparative study revealed an excellent agreement between the dispersion laws ω(B) for the main gapless resonant mode in the AFQ phase subtracted from the ESR measurements and from the neutron scattering in magnetic field data11 This mode corresponding to the g-factor g ~ 1.6–1.7 may be traced up to ω/2π~ 350 GHz for magnetic field aligned along [110] crystallographic direction. Some revisiting of the applicability of the model for interpretation of the high-frequency ESR measurements may be required
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