Spin-Lattice Relaxation in Some Rare-Earth Salts at Helium Temperatures; Observation of the Phonon Bottleneck

Abstract

By observing the transient recovery of microwave paramagnetic resonance signals at p«9.3 kMc/sec and p«34 kMc/sec, we measure the spin-lattice relaxation rate Tr 1 for the rare earth ions Nd, Pr, and Sm in the double nitrate [La 2 Mg3(N03)i2-24H 2 0] and for Ce and Nd in the ethyl sulfate CLa(C2H 6 S04)s-9H 2 OJ in the temperature range 1.4°<r<5°K. We observe the direct process, Tr l <xT; the Orbach process, Ti^ccexpi-A/kT); and the Raman process, Tf 1 oc T 7 and T 9 . The measured relaxation rates are in good agreement with simple theoretical estimates based on Orbach's phenomenological approach. For example, for 1% Nd in the ethyl sulfate with z±H at *>=9.3 kMc/sec we measure Ti~l-I.7r+3.6X10~4T 9 sec -1 , as compared to the theoretical estimate, 2Y-1 = 1.4r+1.3XMW sec" 1 . The data, together with similar measurements by others, lead to the over-all * Research supported in part by the U. S. Atomic Energy Commission and the Office of Naval Research.t Based on part of the Ph.D. dissertation of P. L. Scott,

Magnetocaloric study of spin relaxation in dipolar spin iceDy2Ti2O7

“…8, which confirms a steep thermal dependence of the relaxation in the studied temperature range. We may compare this behaviour with that of a paramagnetic Kramers ion, which typically may relax by the direct, Raman and Orbach processes 36,37 . As shown on the figure, the temperature dependence is close to the T −9 dependence expected for the Raman process.…”

Magneto-Luminescence Correlation in the Textbook Dysprosium(III) Nitrate Single-Ion Magnet

“…To avoid the over-parameterization, the values of m = 9 and n = 1 were fixed to the values found for two-phonon Raman (for Kramers ions) and direct processes [25,26]. The presence of a second relaxation process at a low temperature becomes evident when looking at the Cole-Cole plots (Figure 5a).…”

Phonon bottleneck effect leads to observation of quantum tunneling of the magnetization and butterfly hysteresis loops in(Et4N)3Fe2Schenker1, Leuenberger2, Chaboussant3 et al. 2005Phys. Rev. B

“…The absence of a PB situation is confirmed by the identical relaxation rates 1/τ found for single-crystalline (sample B) and powder samples (sample C) at given values of H DC , as otherwise 1/τ would increase with the size of the crystallites as phonon scattering at the boundary walls decreases. 28,29 With an S = 5 ground state and an energy barrier of ∆ = 2.40 K for spin reversal, Fe 2 features the principal requirements necessary for exhibiting SMM behavior. However, from the absence of a χ" signal at H DC = 0 we conclude that Fe 2 does not behave as an SMM at T ≥ 1.8 K. Obviously at these temperatures the relaxation over the small barrier is beyond the detectable range; presumably the blocking temperature for SMM relaxation lies in the mK region.…”