ESR study of molecular jumps of manganese(II) impurity in single crystals of Cs2HfCl6 and Cs2ZrCl6

Abstract

Electron spin resonance spectra at 35 and 9.3 GHz of Mn2+ impurity ions in single crystals of Cs2HfCl6 and Cs2ZrCl6, from 12 to about 400 K are reported. Below ∼60 K the spectrum consists of a superposition of a number of anisotropic subspectra due to crystallographically equivalent Mn2+ species. Each subspectrum consists of five fine structure bands, due to the different (m−1↔m) transitions, split into six hyperfine components. The spin Hamiltonian of the Mn2+ species in this temperature range is characterized by isotropic g and hyperfine tensors (g=2.004, A=77.0 G) and an almost axially symmetric zero field splitting (ZFS) tensor (D=470 G and E=3 G). It is suggested that the Mn2+ impurity that gives rise to these subspectra consists of MnCl3−5 ions with nearly tetragonal symmetry. The various subspectra correspond to MnCl3−5 ions whose principal ZFS tensor components point along different crystallographic axes. As the temperature is raised above 60 K conspicuous changes occur in the spectrum over an extremely wide range of temperatures: The m≠1/2 fine structure components first broaden and eventually disappear in the noise, while the m=1/2 transitions, due to the different sites, coalesce to give a singly, slightly anisotropic, hyperfine sextet. At high temperatures the full intensity of the spectrum emerges again to give a sharp isotropic sextet. The temperature dependence of the spectrum over the whole temperature range studied can be quantitatively interpreted in terms of a dynamic model in which the major ZFS tensor axis undergoes random jumps between the three crystallographic cubic directions. A general theory for the ESR line shape in the presence of such a process is derived for the case that the ZFS interactions is small compared to the Zeeman energy. Simple and explicit equations are derived for the linewidth and frequency shift in the slow jump limit for the m≠1/2 as well as the m=1/2 fine structure bands. For the fast jump limit the appropriate relaxation matrix is also derived. This theory is then used for a quantitative analysis of the experimental spectra in the CsHfCl6 and CsZrCl6 crystals, and values for the jump rate and the magnetic parameters as function of temperature are derived. It is found that as the temperature is raised from 60 to about 400 K the g value changes from 2.004 to 2.006 and D decreases monotonically from 470 to 330 G. In this temperature range the jump rate changes by about four orders of magnitude and it can be characterized by an Arrhenius plot with the following kinetic parameters: (1.τ)(300 K) =3.5×1011 s−1, ΔE=1.4 kcal/mol. Possible mechanisms for the jump process are discussed.

Characterization of the Dynamics in the Protonic Conductor CsH2PO4 by 17O Solid-State NMR Spectroscopy and First-Principles Calculations: Correlating Phosphate and Protonic Motion

“…A dynamically averaged line shape is now obtained for each of the O1, O2 and O3 oxygen atoms. Since it is not appropriate to describe a dynamically averaged second-order quadrupole broadened line shape with an exchange-averaged tensor 49 (for example, even isotropic motion that is sufficiently fast to average the second-order quadrupolar effects, but not the first order quadrupolar interaction, will not remove the quadrupolar induced shift 50 ), no corresponding NMR parameters for this simulation are given in Table 1 . Instead, the simulated spectrum should be directly compared with experiment, the spectrum obtained with this model showing very good overall agreement with experiment, the discontinuities associated with the unresolved O2 and O3 resonances being well reproduced.…”

The highly resolved electronic spectrum of the square planar CuCl42− ion

“…The host lattice is reported to both cleave along the ͑111͒ planes, 9 and along cubic directions. 10 Here we have used the ͑001͒ face for MCD measurements.…”

Electron spin resonance investigation ofMn2+ions and their dynamics in Mn-dopedSrTiO3Laguta1, Кондакова2, Bykov3 et al. 2007Phys. Rev. B575500View full textAdd to dashboardCite

“…temperatures, 0 T → [1]. Owing to the unusually high polarizability, various types of polar phases (dipole ferro-glass and ferroelectric) can be induced by dipole impurities [2] or by pressure [3] and by 18 O isotope exchange [4,5]. From this point of view, SrTiO 3 is a promising material for many future applications of ferroelectrics, especially at cryogenic temperatures.…”