Absence Of Exchange Interaction Research Articles

Crystal field effects in the ESR spectra of Ce1- xRExFe4P12( RE = Gd, Dy, Er)

Low temperature ( 1.5 – 4.2K ) ESR experiments of diluted S( Gd 3+) and non- S( Dy 3+ , Er 3+ ) rare-earths ( REs) in single crystals of the semiconducting compound CeFe 4 P 12 show that the REs impurities are located in cubic sites, substituting probably the Ce atoms. Although metallic-like resonance shapes were observed in all cases, the measured g-values, hyperfine constants and temperature dependence of the linewidth, seem to indicate the absence of exchange interaction between the localized RE's magnetic moment and the host's conduction electrons. Doped and undoped samples all show extra anisotropic lines which were tentatively attributed to defects associated to Ce 3+ ions located at sites of lower symmetry.

A magnetic susceptibility and Mössbauer spectroscopy study of bis(thiosemicarbazide)iron(II) sulfate. A case of zero field splitting

The magnetic susceptibility of a polycrystalline powder sample of bis(thiosemicarbazide)iron(II) sulfate, a sulfato bridged polymer, has been determined over the range 100 K to 2 K using vibrating sample magnetometry. The susceptibility behavior is interpreted in terms of zero field splitting (∣D∣ ∼ 5 cm −1) of the spin quintet ground state and an absence of exchange interaction.

Crystal electric field and magnetic-ion-lattice interactions in TmZn

Experimental results on magnetic and elastic properties for the cubic intermetallic compound TmZn are presented. The magnetic-susceptibility measurement gives a ferromagnetic ordering temperature of ${T}_{c}=10$ K and an effective Bohr magneton number $g{[J(J+1)]}^{\frac{1}{2}}=7.67$. We can interpret the high-field (up to 125 kOe) magnetization curves for $Tl{T}_{c}$ using the crystal-field split $^{3}H_{6}$ ground state for the ${\mathrm{Tm}}^{3+}$ ion. For the cubic crystal-field parameters we obtain ${A}_{4}〈{r}^{4}〉=\ensuremath{-}170\ifmmode\pm\else\textpm\fi{}20$ K, ${A}_{6}〈{r}^{6}〉=\ensuremath{-}10\ifmmode\pm\else\textpm\fi{}3$ K. The elastic constant ${c}_{11}\ensuremath{-}{c}_{12}$ shows a softening of 40% from room temperature down to 13 K. The ${c}_{44}$ mode and the bulk modulus show a normal temperature dependence for $Tg{T}_{c}$. We interpret the temperature dependence of the ${c}_{11}\ensuremath{-}{c}_{12}$ mode as due to a crystal-field effect, which is particularly pronounced in TmZn because the crystal-field ground state is a doublet ${\ensuremath{\Gamma}}_{3}$. The magnetoelastic coupling constant ${g}_{2}^{2}=8.9$ mK together with an additional quadrupole-quadrupole coupling constant ${g}^{\ensuremath{'}}=\ensuremath{-}9.6$ mK are not strong enough to induce a structural transition in the absence of exchange interactions. We compare these results to the recently investigated TmCd compound, which exhibits no magnetic transition but a structural transition at ${T}_{a}=3.16$ K.

On the behaviour of the spin relaxation function

The integrodifferential equation governing the time behaviour of the longitudinal spin relaxation function in the high-temperature approximation is studied. The analysis clarifies the consistency of possible approximations to the kernel with the asymptotic behaviour of the solution. It is found that the presence or absence of exchange interaction leads to completely different behaviours in the coupling constant λ. Correspondingly different approximation schemes are allowed. An expression for the solution, of rather general validity, is given. This expression is correct up to terms of second order in the coupling constant and is obtained directly by quadrature on the kernel.

On the Theory of Cross Relaxation in Maser Materials II. Harmonic Spin Coupling

The harmonic cross relaxation mainly due to the interaction of neighboring three spins has been studied under the moment method in succession to the previous paper. It is shown that in the absence of exchange interaction the shape functions of the relaxation are nearly Gaussian the frequency widths of which are much greater than those of magnetic resonance absorption. The rate of relaxation is calculated in cases of S =1, and 3/2. The observed cross relaxation times in ruby are compared with the theoretical values given by an approximate method. It is shown that the experimental results are at least numerically interpreted by the flipping of spins due to the dipole-dipole interaction between ions except for those estimated to be closely coupled by exchange interaction.