Spin-lattice Coefficients Research Articles

Temperature Dependence of the Spin-Lattice Interaction forGd3+in ThO2and CeO2

The second- and fourth-order spin-lattice coefficients of ${\mathrm{Gd}}^{3+}$ in cubic positions of Th${\mathrm{O}}_{2}$ and Ce${\mathrm{O}}_{2}$ crystals have been measured as a function of temperature between 4 and 360 \ifmmode^\circ\else\textdegree\fi{}K by electron-paramagnetic-resonance experiments in uniaxially stressed crystals. The second-order coefficients are considerably different for the two crystals, and these coefficients show a large variation with temperature. A detailed theoretical calculation of these coefficients has not been carried out; however, it is possible to qualitatively interpret the observed temperature variation in terms of effects due to the modulation of the orbit-lattice interaction by the lattice vibrations. The temperature-variation curves are explained using an Einstein model for the vibrations of the oxygen ligands of the paramagnetic ions. The fourth-order coefficients are similar for the two crystals and are temperature independent in the range studied. The effect of a hydrostatic strain on the energy levels of the ion is used to explain the observed temperature variation of the cubic field parameter in terms of the thermal expansion of the crystal.

The spin-lattice interaction for rare earth S-state ions

We report values of the second and fourth order spin-lattice coefficients of Gd 3+ in SrO and CdF 2 measured in uniaxial stress EPR experiments at 290°K and 32 GHz. A previous measurement in Gd 3+ in CaF 2 was repeated in order to obtain more accurate values for the fourth order coefficients. We find: G (2) 3 g = (0·21 ± 0·02) cm −1, G (2) 5 g = (−0·40±0·06) cm −1 and G (4) 1 g = (2·5±1·2) 10 −4 cm −1 for Gd 3+ in SrO; G (2) 3 g = (−0·24±0·02) cm −1, G (2) 5 g = (−0·061±0·008) cm −1, G (4) 1 g = (1·5±0·9) 10 −4 cm −1 and G (4) 3 g = (−4·6±2·9) 10 −4 cm −1 for Gd 3+ in CdF 2 and G (4) 1 g = (1·6±0·6) 10 −4 cm −1 and G (4) 3 g = (−1·9±1·2) 10 −4 cm −1 for Gd 3+ in CaF 2. These values are compared with those obtained for Gd 3+ and Eu 2+ in other cubic crystals by uniaxial and hydrostatic stress experiments.

Calculation of the Spin-Lattice Coefficients ofGd3+in CaF2Using a Point-Charge Model for the Crystalline Field

The contribution of the Blume-Orbach mechanism to the second-order spin-lattice coefficients for ${\mathrm{Gd}}^{3+}$ in cubic sites of Ca${\mathrm{F}}_{2}$ has been calculated with a point-charge approach for the orbit-lattice interaction. Our results, ${G}_{3g}^{(2)}=\ensuremath{-}0.006$ ${\mathrm{cm}}^{\ensuremath{-}1}$ and ${G}_{5g}^{(2)}=\ensuremath{-}0.07$ ${\mathrm{cm}}^{\ensuremath{-}1}$, agree in sign with the experimental values of ${G}_{3g}^{(2)}=\ensuremath{-}0.22$ ${\mathrm{cm}}^{\ensuremath{-}1}$ and ${G}_{5g}^{(2)}=\ensuremath{-}0.11$ ${\mathrm{cm}}^{\ensuremath{-}1}$. Differences in magnitude of ${G}_{3g}^{(2)}$ can be understood in view of the opposite contribution of the fourth- and sixth-order terms of the orbit-lattice Hamiltonian. We conclude that the Blume-Orbach mechanism predicts values for the spin-lattice coefficients ${G}_{3g}^{(2)}$ and ${G}_{5g}^{(2)}$ of ${\mathrm{Gd}}^{3+}$ in Ca${\mathrm{F}}_{2}$ in reasonable agreement with the experimental data, and that the cubic crystalline field must be considered in any calculation of the spin-lattice parameters.

Second and fourth order spin-lattice coefficients for Gd 3+ in thoria

We measured the EPR lineshifts for Gd 3+: ThO 2 under uniaxial stress. Values are given for the second and fourth order spin lattice strain coefficients.

Spin-lattice coefficients for substitutionaL Gd3+ in CaF2

For the purpose of evaluating the spin-lattice coefficients C11 and C44, for CaF2:Gd3+ in cubic sites, uniaxial stress studies were conducted at room temperature on a single crystal of CaF2 doped with 0.02 at. % Gd3. From the measured shifts of the magnetic field positions of certain of the fine structure components, corresponding to known increments in applied stress, the spinlattice coefficients were evaluated in magnitude and sign. Taking compressive stress as negative, the experimentally determined values are C11 = −2.4 ± 0.8 × 10−13cmdyn and C44 = −5.5 ± 1.1 × 10−13cmdyn.

Spin-lattice coefficients for substitutional Gd 3+ in CaF 2

Essential oils (EOs) from Origanum vulgare subsp. vulgare (OVV) and O. vulgare subsp. hirtum (OVH) were evaluated for antioxidant activities (DPPH, ABTS, FRAP, CUPRAC, β-carotene/linoleic acid, phosphomolybdenum and metal chelating), antimicrobial and inhibitory properties against acetylcholinesterase, butrylcholinesterase, tyrosinase, α-amylase and α-glucosidase. Thymol and linalool were identified as major component in OVV and OVH essential oils, respectively. O. vulgare subsp. vulgare exhibited a strong free radical scavenging, reducing power, antimicrobial and acetylcholinesterase, butrylcholinesterase, α-amylase and α-glucosidase inhibitory activity. Interestingly, OVH possess a significant metal chelating and tyrosinase inhibitory activities. The EOs of both species exhibited moderate antibacterial and antifungal activities. The MIC values of the EOs ranged from 85.3 to 426.7 μg/mL. O. vulgare subsp. vulgare showed higher activity against Sarcina lutea with the lowest MIC (85.3 μg/mL), whereas OVH indicated strong activity for Candida albicans with MIC value of 85.3 μg/mL. The data suggest that the Origanum EOs could be used as valuable new natural agents with functional properties for food and pharmacology industries.

Spin-Lattice Coefficients forGd3+andEu2+in CaF2and forGd3+in CaO

We have measured the spin-lattice coefficients of ${\mathrm{Eu}}^{2+}$ and ${\mathrm{Gd}}^{3+}$ in Ca${\mathrm{F}}_{2}$ and ${\mathrm{Gd}}^{3+}$ in CaO by studying the effect of uniaxial stress on the EPR spectra of these ions. The experimental data show that fourth-order terms in the spin-lattice Hamiltonian give significant contributions. The values of the second-order spin-lattice coefficients are given, and the fourth-order contribution is tentatively identified as due to the change of the cubic field splitting with stress. From the value of the fourth-order coefficient, we conclude that at least half of the temperature dependence of the cubic field parameter is due to the effect of the lattice expansion.

Antiferromagnetic Resonance in RbMnF3Under Axial Stress

Magnetoelastic constants of antiferromagnetic RbMn${\mathrm{F}}_{3}$ were determined at 4.2\ifmmode^\circ\else\textdegree\fi{}K from the stress and field dependence of AFMR frequency: ${b}_{1}=1.5\ifmmode\times\else\texttimes\fi{}{10}^{6}$ and ${b}_{2}=0.17\ifmmode\times\else\texttimes\fi{}{10}^{6}$ erg/${\mathrm{cm}}^{3}$; linewidths are accounted for by inhomogeneous strain broadening. Spin-lattice strain coefficients for ${\mathrm{Mn}}^{++}$ in a regular ${\mathrm{F}}^{\ensuremath{-}}$ octahedron were derived as ${G}_{11}=0.32$ and ${G}_{44}=\ensuremath{-}0.073$ (${\mathrm{cm}}^{\ensuremath{-}1}$/ion) after correcting the $b'\mathrm{s}$ for magnetic dipolar contributions.

Effect of Uniaxial Stresses on the Paramagnetic Spectra ofMn3+andFe3+in MgO

We have investigated the lowest energy levels of the paramagnetic ions ${\mathrm{Mn}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ in the host crystal MgO, as a function of externally applied uniaxial stress. The effect of the stress on the energy levels of the paramagnetic ion can be described by introducing into the spin Hamiltonian an additional term of the form $\mathrm{S}\ifmmode\cdot\else\textperiodcentered\fi{}D\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{S}$. When the components of $D$ are expressed as linear functions of the applied stress components, there are only two independent constants of proportionality in our simple case of a cubic crystalline lattice. We have experimentally determined these two constants, i.e., spin-lattice coefficients ${C}_{11}$ and ${C}_{44}$, for ${\mathrm{Mn}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ in MgO, and find them to be, in units of ${10}^{\ensuremath{-}13}$ cm/dyne: for ${\mathrm{Mn}}^{2+}$, ${C}_{11}=(+7.1\ifmmode\pm\else\textpm\fi{}3)%$ and ${C}_{44}=(\ensuremath{-}2.1\ifmmode\pm\else\textpm\fi{}3)%$; for ${\mathrm{Fe}}^{3+}$, ${C}_{11}=(+26\ifmmode\pm\else\textpm\fi{}3)%$ and ${C}_{44}=(\ensuremath{-}5.5\ifmmode\pm\else\textpm\fi{}5)%$. We have also investigated the absolute value and the angular dependence of the linewidth of the fine structure of ${\mathrm{Mn}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ in MgO. We can account for these widths in terms of the spin-lattice coefficients, by assuming a random distribution of internal stresses in the host sample. We also indicate the relevance of the spin-lattice coefficients in the determination of the direct spin-lattice relaxation times.