Evolution of spin relaxation processes in LiY${}_{1-x}$Ho${}_x$F${}_4$ with increasing x studied via AC-susceptibility and muon spin relaxation

Abstract

We present measurements of magnetic field and frequency dependences of the low temperature (T = 1.8 K) AC-susceptibility, and temperature and field dependences of the longitudinal field positive muon spin relaxation (μSR) for LiY${}_{1-x}$Ho${}_x$F${}_4$ with x = 0.0017, 0.0085, 0.0408, and 0.0855. The fits of numerical simulations to the susceptibility data for the x = 0.0017, 0.0085 and 0.0408 show that Ho-Ho cross-relaxation processes become more important at higher concentrations, signaling the crossover from single-ion to correlated behavior. We simulate the muon spin depolarization using the parameters extracted from the susceptibility, and the simulations agree well with our data for samples with x = 0.0017 and 0.0085. The μSR data for samples with x = 0.0408 and 0.0855 at low temperatures (T < 10 K) cannot be described within a single-ion picture of magnetic field fluctuations and give evidence for additional mechanisms of depolarization due to Ho${}^{3+}$ correlations. We also observe an unusual peak in the magnetic field dependence of the muon relaxation rate in the temperature interval 10 - 20 K that we ascribe to a modification of the Ho${}^{3+}$ fluctuation rate due to a field induced shift of the energy gap between the ground and the first excited doublet crystal field states relative to a peak in the phonon density of states centered near 63 cm${}^{-1}$.

33 pages, 9 figures; accepted for publication, Physical Review B

References in corpus (5)

• Spin dynamics and magnetic order in magnetically frustrated Tb2Sn2O7
• Quantum and Classical Glass Transitions in $LiH{o}_x{Y}_{1-x}{F}_4$
• Absence of Conventional Spin-Glass Transition in the Ising Dipolar System LiHo_xY_{1-x}F_4
• Cross-relaxation and phonon bottleneck effects on magnetization dynamics in LiYF4:Ho3+
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• Microscopic model of spin flip-flop processes in rare-earth-ion-doped crystals
• Experimental measurement of the isolated magnetic susceptibility