29 research outputs found
Magnetic-field and doping dependence of low-energy spin fluctuations in the antiferroquadrupolar compound Ce(1-x)La(x)B(6)
CeB(6) is a model compound exhibiting antiferroquadrupolar (AFQ) order, its
magnetic properties being typically interpreted within localized models. More
recently, the observation of strong and sharp magnetic exciton modes forming in
its antiferromagnetic (AFM) state at both ferromagnetic and AFQ wave vectors
suggested a significant contribution of itinerant electrons to the spin
dynamics. Here we investigate the evolution of the AFQ excitation upon the
application of an external magnetic field and the substitution of Ce with
non-magnetic La, both parameters known to suppress the AFM phase. We find that
the exciton energy decreases proportionally to T_N upon doping. In field, its
intensity is suppressed, while its energy remains constant. Its disappearance
above the critical field of the AFM phase is preceded by the formation of two
modes, whose energies grow linearly with magnetic field upon entering the AFQ
phase. These findings suggest a crossover from itinerant to localized spin
dynamics between the two phases, the coupling to heavy-fermion quasiparticles
being crucial for a comprehensive description of the magnon spectrum.Comment: Extended version with a longer introduction and an additional figure.
6 pages and 5 figure
Magnetic field dependence of the neutron spin resonance in CeB6
In zero magnetic field, the famous neutron spin resonance in the f-electron
superconductor CeCoIn5 is similar to the recently discovered exciton peak in
the non-superconducting CeB6. Magnetic field splits the resonance in CeCoIn5
into two components, indicating that it is a doublet. Here we employ inelastic
neutron scattering (INS) to scrutinize the field dependence of spin
fluctuations in CeB6. The exciton shows a markedly different behavior without
any field splitting. Instead, we observe a second field-induced magnon whose
energy increases with field. At the ferromagnetic zone center, however, we find
only a single mode with a non-monotonic field dependence. At low fields, it is
initially suppressed to zero together with the antiferromagnetic order
parameter, but then reappears at higher fields inside the hidden-order phase,
following the energy of an electron spin resonance (ESR). This is a unique
example of a ferromagnetic resonance in a heavy-fermion metal seen by both ESR
and INS consistently over a broad range of magnetic fields.Comment: 7 pages, 6 figures including one animation, accepted to Phys. Rev.
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Reversible and irreversible magnetocaloric effect: The cases of rare-earth intermetallics YbPt<sub>2</sub>Sn and Ce<sub>0.5</sub>La<sub>0.5</sub>B<sub>6</sub>
Magnetocaloric effect (MCE) has drawn much attention because its magnetic cooling property enables refrigeration without producing noxious gas or using rapidly depleting resources. However, applications for everyday life are yet distant. In addition, we need to understand more about the practical aspect of the MCE. Here, we introduce a phenomenological model to explain the quasi-adiabatic MCE. Correction factors to the equilibrium thermodynamic feature implied by the entropy landscape are devised in analytic forms. To demonstrate the validity of the model, the MCE from two different materials is investigated. The recently discovered metallic paramagnet, YbPt2Sn, shows a linear and reversible MCE which is typical of a paramagnetic system and suitable for cryogenics without 3He. On the other hand, a complex-phase material, Ce0.5La0.5B6, exhibits a pronounced irreversible MCE especially across a magnetic phase boundary. A term that describes the field induced heating near a phase transition turns out to be essential in resolving the irreversible, non-equilibrium MCE. © 201