Jan Smit

Mössbauer Effect in Lithium‐Zinc Ferrites

Mossbauer effect measurements have been made on 57Fe in the lithium‐zinc ferrites, ZnxLi0.5 − x/2Fe2.5 − x/2O4, for 0≤x≤1 and at temperatures from 22° to 700°C. The spectra taken at 22° and 330°C are fit by a superposition of components due to ions on tetrahedral sites and on octahedral sites with different numbers of magnetic neighbors. Calculations of the saturation magnetizations based upon the Mossbauer results and the assumption that no significant spin canting occurs are in good agreement with published experimental data. The variation with x of the quadrupole splitting is determined from spectra taken above the Curie temperatures of all samples.

Multiple-phonon resonant Raman scattering theory☆

Abstract Multiple-phonon Raman scattering in CdS is explained by a model in which resonant absorption occurs for electronically and vibrationally excited localized states. The radius of the localized state is estimated to be about 20 A.

Ion configuration in spinels

Abstract The polarization of the anions in spinels can stabilize particular ion configurations like Cu 1+ Cr 3+ Ti 4+ S 4 2− .

Nuclear magnetic resonance and relaxation of the Heusler alloy

Abstract NMR of the Heusler alloy Cu 2 MnAl has been studied for all three nuclei by using the spin echo method. The resonance frequencies at 4.2°K are 240 and 257 MHz for Cu 63 and Cu 65 respectively, 225 MHz for Mn 55 and 76 MHz for Al 27 . The hyperfine fields are −212 and −213 KG for Cu and Mn respectively, and 68.2 KG for Al, the sign of which could not be determined. The temperature variation of the Mn hyperfine field is within 1 2 per cent the same as that of the magnetization whereas the Cu hyperfine field decreases more with increasing T . The spin echo amplitude as a function of the applied static field shows a maximum which is caused by an increase of the relaxation times with increasing static field for resonances in both walls and domains. A discussion about the signs and the magnitudes of the hyperfine fields at the nuclei is included.

Mechanism for the Direct Exchange Interaction of Europium in Compounds with Rocksalt Structure

From the strong decrease in the nearest‐neighbor exchange interaction going from EuO to EuS, EuSe, EuTe, it has been concluded that this positive interaction must be caused by direct orbital overlap. Since the 4f cores are very small, this has to occur via partial occupation of outer orbits. The excitation to the 5d wave function by zero point lattice vibrations has been considered and is thought to be responsible for the ferromagnetism of these compounds. The order of magnitude has been estimated and agrees with experiment.

On the signs of the elasto‐optic coefficients

It is shown that the strain‐induced dipole‐dipole interaction gives a major contribution to the elasto‐optic effect and can explain the opposite signs of the two shear coefficients observed in most alkali halides and alkaline‐earth fluorides.

Ferromagnetic Resonance in Si‐Doped YIG

The magnetocrystalline anisotropy of Fe2+ ions in YIG has been studied by means of FMR at 10 and 30 GHz at temperatures between 4° and 400°K. Below 50°K strong magnetic anneal occurs. Anneal fields were in the [100], [111], and [110] directions. The g factor is 1.98 at 4.2°K and 1.96 at 290°K. At low temperature the resonance field HR is less than ω/γ by as much as 2000 Oe for all orientations in the (110) plane. The HR versus angle curves are explained quantitatively by taking into account canting of the spins around the Fe2+ ions as well as perturbing electrostatic fields of the neighboring Si ions. The correct temperature dependence and anisotropy of the linewidth ΔH also follow from the model calculation.

Application of the Rudermann—Kittel Interaction to Metals

The indirect exchange interaction of magnetic cores via the conduction electrons has been calculated on the basis of a simple model, and the original Rudermann—Kittel result was found provided that (3m/4πℏ2) × J SkF≪1, where J is the exchange interaction between the conduction electrons and the magnetic core electrons, and kF the radius of the Fermi sphere. For the usual values J = 5 eV·A3, kF = 1 A−1, and the spin S = 3, this parameter is 0.5. The zero points of the oscillatory interaction from this analysis may be particularly unreliable.

On the helix-ferro transition in MnP

Abstract The decrease in the ratio of the exchange constants J2 and J1 gives for a special value of the anisotropy energy a first-order phase transition.

Nuclear magnetic resonance in NiCu, Zn and Ga alloys☆

Abstract NMR of 61Ni, 63Cu, 65Cu, 69Ga, and 71Ga has been observed in ferromagnetic alloys of nickel with up to 10 at. % of Cu, Zn or Ga. From an analysis of the structure of the complex spectra it is concluded that the excess electrons stay localized around the solute atoms. The hyperfine field of Ga at 4.2°K is 23 koe.