Angular Dependences of ESR Parameters in Antiferroquadrupolar Phase of CeB₆

Abstract

Angular dependences of ESR line parameters (g-factor and linewidth ∆H) were experimentally explored in the antiferroquadrupolar phase of heavy fermion system CeB6 at T = 1.8 K. The data were obtained in two experimental geometries with different mutual directions of the wavevector k and the external magnetic field H at frequency of f = 60 GHz. A g-factor anisotropy was found: while g-factors for [110] and [111] directions are close to each other (g ≈ 1.6), it is considerably higher (g ≈ 1.75) for [100]. The obtained angular dependence g(Θ) was compared with the theoretically predicted g-factor behavior for the Γ8 state of Ce 3+ ion in antiferroquadrupolar phase of CeB6. It turns out that the experimental g-factor is considerably smaller at all angles than the theoretically calculated limits (2 < g < 2.2) and, moreover, it has a different symmetry. This result together with the strong linewidth anisotropy ∆H(Θ) demonstrates that for the relevant description of experimental data the theoretical model should take into account also the interaction of Ce 3+ ion with itinerant 5d electrons.

Field-Angle-Resolved Magnetic Excitations as a Probe of Hidden-Order Symmetry inCeB6

“…At first glance, this conclusion may seem to be in contradiction with the recent ESR results by Semeno et al [65][66][67]. In this experiment, the energy of the zone-center magnetic resonance has been measured for different directions of the magnetic field between B [110] and B [001], revealing a significant (∼10%) anisotropy in the g-factor with a strong temperature dependence, which was most pronounced for B [001].…”

“…8 marks the region in the B-T parameter space covered by the data in Refs. [65][66][67], while the blue squares mark the positions of the 60 GHz resonance at different temperatures. In this representation, it becomes obvious that the field scans in the low-temperature region cross the phase boundary between the AFM and AFQ phases, where the magnetic excitation spectrum becomes quasielastic [43] and gets broadened by the critical fluctuations of both order parameters.…”

“…10. On the other hand, the low-energy modes are stabilized directly by the Zeeman term and show an approximately linear increase in frequency and splitting with the field, with the slope given by the effective g-factor that can be anisotropic with respect to the field direction [65][66][67]. At sufficiently high fields, these modes intersect with the high-energy modes, which leads to a complex hybridization pattern with multiple avoided mode crossings.…”

“…. The red rectangle shows the part of the phase diagram covered by ESR measurements of the temperature-dependent g-factor by Semeno et al[65,66]. Blue squares mark the positions of the 60 GHz resonance at different temperatures.…”

Neutron-scattering studies of spin dynamics in pure and doped CeB6

“…For lower fields, however, the anisotropy is reduced, which is a direct consequence of the initially nonlinear field dependence of the low-energy mode. Indeed, the g-factor anisotropy reported from previous ESR measurements [125][126][127], which were performed at magnetic fields of ∼ 3 T, is several times smaller and constitutes a relative change of less than 10% between the [100] and [111] field directions. However, the overall shape of the anisotropic g-factor dependence turns out to be the same in ESR and INS measurements and agrees well with the results of model calculations by Schlottmann [121][122][123].…”