Direct measurements of anticrossings of the electron-nuclear energy levels in LiYF4∶Ho3+ with submillimeter EPR spectroscopy

Abstract

The electron paramagnetic resonance (EPR) spectra of impurity Ho 3+ ions in monocrystals LiYF.~:Ho 3 § (0.1 and 1%) with the natural abundance of 6Li (7.42%) and 7Li (92.58%) isotopes, and in the sample 7LiYF4:Ho3+ (0.1%) isotopically pure in 7Li were taken at the temperature 4.2 K in the frequency range of 165-285 GHz. Resonance transitions between crystal field sublevels (the ground non-Kramers doublet and the nearest excited singlet) of the 518 term were detected. The refined set of crysta] field parameters and the effective constant of the magnetic hyperfine interaction were determined from the detailed analysis of the recorded spectra at frequencies varied by 0.05 GHz. The fine structure of EPR lines with intervals of about 300 MHz observed in the sample LiYF4:Ho 3+ (0.1%) can be interpreted as a result of the isotopic disorder in the Li sublattices. Direct information about energy gaps at the anticrossing points of the electron-nuclear sublevels of the ground doublet was obtained. These gaps are induced by the hyperfine interaction that mixes doublet and singlet states and by random crystal fields. Weak EPR signals from distorted single ion and pair centers of impurity Ho 3+ ions were resolved. From a comparison of the measured and simulated spectra, estimates of spectral parameters of the dimer centers have been obtained.

19F nuclear spin relaxation and spin diffusion effects in the single-ion magnet LiYF4:Ho3+

“…Additional gaps of comparable magnitude at the odd crossing points for Δm = 0 are induced by random crystal fields [26]. The magnetic field dependence of the relaxation rate was studied at temperatures 1.7 -4.2 K in the range of magnetic fields from 0.1 to 0.2 T for different angles between the field and the c-axis (the data for θ ~ 30 0 were presented earlier in Ref.…”

“…There is only one holmium isotope, 165 Ho, with nuclear spin I = 7/2. The free ion ground state, the 5 I 8 multiplet, is split by the tetragonal crystal field into 13 sublevels with a Γ 34 doublet ground state and the first excited Γ 2 singlet at 6.85 cm -1 higher energy (here Γ is the corresponding irreducible representation of the S 4 point symmetry group) [26,27]. The electronic and nuclear states are mixed mainly by the magnetic hyperfine interaction H hf =A (A = 0.795 GHz [26]).…”

“…The free ion ground state, the 5 I 8 multiplet, is split by the tetragonal crystal field into 13 sublevels with a Γ 34 doublet ground state and the first excited Γ 2 singlet at 6.85 cm -1 higher energy (here Γ is the corresponding irreducible representation of the S 4 point symmetry group) [26,27]. The electronic and nuclear states are mixed mainly by the magnetic hyperfine interaction H hf =A (A = 0.795 GHz [26]). The calculated hyperfine structure of ⋅ J I the ground electronic doublet (the corresponding g-factors equal g || =13.3, =0 [26]) in the external magnetic field B(sinθ cosϕ, sinθ sinϕ, cosθ) with the orientation defined by angles θ = 27.5 0 and ϕ = 45 0 relative to the crystallographic axes (z||c, x||a) is shown in Fig.…”

Relaxation rates of magnetization in LiYF4:Ho3+ crystals

“…The mixing of the ground doublet with the excited singlets by the magnetic hyperfine interaction opens the gaps at the odd crossing (anti-crossing) points with the maximum values about 0.35 GHz for m I = 2 [9]. At low temperatures interactions between Ho 3+ ions play an important role in relaxation processes in the coupled electron-nuclear subsystem [1,2].…”

Evolution of spin relaxation processes in LiY1−xHoxF4Johnson1, Малкин2, Lord3 et al. 2012Phys. Rev. BSelf Cite8070View full textAdd to dashboardCite

“…All concentration-independent parameters which we use in simulations of the AC-susceptibilities have been determined in previous studies of optical and EPR spectra, 19 F nuclear spin relaxation and AC-susceptibilities in low-x LiY 1-x Ho x F 4 samples (x ≤ 0.0027). 6,7,8,24 In particular, crystal field parameters in the Hamiltonian H CF and electron-phonon coupling constants used in calculations of the relaxation rates are given in Table I …”