Multiple-timescale relaxation dynamics in CsGd(MoO₄)₂—a dipolar magnet with a highly anisotropic layered crystal structure

Abstract

The dynamic properties of the dipolar magnet CsGd(MoO4)2 have been studied. The frequency and temperature dependence of the AC susceptibility investigated in the paramagnetic region above 2 K revealed the co-existence of magnetic field induced slow and fast relaxation channels with a timescale differing by three orders of magnitude. The slow relaxation is determined by the properties of the first coordination sphere of the Gd(3+) ion and has the character of a two-phonon Orbach process. The fast relaxation is potentially attributed to a two-phonon Raman process realized via a localized phonon mode associated with the layered crystal structure. The temperature dependence of the phonon mean free path in zero magnetic field indicates significant phonon scattering below 1 K resulting from the combined effect of magnetic correlations and the scattering of dominant phonons with energies corresponding to the crystal-field levels.

Impact of the crystal electric field on magnetocaloric properties of CsGd(MoO4)2

“…Unlike previous analysis [24], the existence of plateau below 1 K should result from the scattering of phonons on the internal surfaces of this highly anisotropic material with a layered structure. While the low-temperature end of the plateau nicely correlates with the magnetic phase transition at 0.45 K, further decrease of L with a minimum appearing at 0.2 K can be attributed to the one-magnonone-phonon resonance phonon scattering [35].…”

“…O q k represents equivalent operators and B q k are crystal-field parameters. Previous reports [24,27] estimated crystal-field splitting of the ground state by considering the axial symmetry of the crystal field characterized by the parameter B 0 2 = -0.089 K. Corresponding easy axis is parallel to the crystallographic axis a [25].…”

“…The compound together with other materials from the series of rare-earth double molybdates MR(MoO 4 ) 2 (M + is an alkali-metal ion and R 3+ is a rare-earth ion) belongs to laser active materials [21,22,23]. Besides their potential use in the optoelectronic devices at room-temperature applications, the compounds possess interesting magnetic properties at low temperatures [24,25]. Previous low-temperature studies [26,27,28,29,30,24] considered this material as a quasi-one dimensional dipolar magnet with a magnetic phase transition to the ordered state at T C = 0.45 K. The effective strength of dipolar interactions was estimated in the form of the effective intra-chain coupling parameter J/k B ≈ 0.6 K and interchain coupling J ′ < 0.03 J [27].…”

Slow magnetic relaxation in Ni–Ln (Ln = Ce, Gd, Dy) dinuclear complexes

“…Two slow relaxation processes have also been described for several Gd(III) compounds. 20,22,23,28,29 For instance, for a Gd(III)EDTA chelate compound, 29 the values of U eff = 6.1 K (τ = 4 × 10 −2 s) and U eff = 84 K (τ = 8 × 10 −7 s) were reported (B DC = 0.45 T). The geometry and the electron density of the coordination sites has been proved to exert a very important influence on the SMM behaviour of lanthanide ions.…”

“…Despite its essentially isotropic ground state with L = 0, several materials have been reported for which magnetic anisotropy around the gadolinium(III) centre was induced by local coordination, magnetic exchange coupling or electron density donation. [20][21][22][23][24][25][26][27][28][29] These materials containing gadolinium(III) may be considered as members of a new class of SMMs with the highest known spin state (4f 7 ) for a single ion.…”