H. W. de Wijn

Magnetic Susceptibilities of Rare‐Earth–Indium Compounds: RIn3

The magnetic properties and the lattice parameters for 13 compounds of the composition RIn3 (Cu3Au structure) are reported. The magnetic measurements have been performed between 4.2° and 500°K with magnetic fields up to 30 kOe. With the exception of compounds with R=La, Sm, Y, and Yb Curie–Weiss behavior is observed in the high‐temperature region. At low temperatures the magnetic behavior for compounds in which R=Ce, Nd, Sm, Gd, Tb, Dy, Ho, and Er is ascribed to antiferromagnetic ordering. In the case of PrIn3 magnetic ordering is prevented by crystalline fields. The splitting of the J = 4 state of Pr3+ by cubic crystalline fields has been calculated for various combinations of fourth‐ and sixth‐order potentials. Possible energy diagrams are presented.

Crystal-field anisotropy of Sm3+ in SmCo5

It is shown that the major contribution to the high uniaxial anisotropy of the compound SmCo5 arises from the action of crystalline and exchange fields on the Sm3+ ion.

Effect of Quenching of Polarizations in Polar Diatomic Molecules on Nuclear‐Quadrupole Coupling, Its Vibrational Dependence, and Molecular Dipole Moments

A simple model is added to the theory of nuclear‐quadrupole coupling, which together with the existing theories, viz., the Townes and Dailey theory and the theory of the antishielding effect, accounts for experimental data on nuclear‐quadrupole coupling in the alkali halides. In the ionic configuration of the molecule the polarizations mainly of the halogen ions are assumed to be quenched by the repulsive forces between the ions, insofar as they involve expansion of electron density on the side adjacent to the core of the other ion. For halogen ions this results in a contribution to the electric‐field gradient from dipolar polarization, while the antishielding effect is suppressed. This contribution is evaluated by use of experimental data of free halogens. For alkali ions the antishielding effect remains operative. Expressions are derived for the dependence of nuclear‐quadrupole coupling on the vibrational state. Quenching of the polarization of halogen ions is also included in Rittners theory of the el...

Temperature dependence of the EPR linewidth in K2MnF4 and Rb2MnF4

Abstract EPR linewidths of Mn2+ in the quadratic layer antiferromagnets K2MnF4 and Rb2MnF4 have been measured at 24 GHz from 80 K downwards and found to increase steadily as TN is approached. The region of enhancement extends further above TN than is the case in MnF2, a three-dimensional system.

Magnetic Properties and Nuclear Magnetic Resonance of Cubic RCu5 Intermetallic Compounds

The magnetic properties of the cubic RCu5 compounds TbCu5, DyCu5, HoCu5, ErCu5, and TmCu5 are reported for temperatures between 2.1° and 300°K. In the paramagnetic region the susceptibility follows a Curie‐Weiss law. The type of ordering at low temperatures changes with increasing atomic number from antiferromagnetic (R = Tb) to ferromagnetic (R = Ho, Er, Tm), while DyCu5 is metamagnetic. The Knight shifts of the 63Cu NMR in these compounds have been measured between 100° and 300°K. The results are discussed in terms of the Ruderman‐Kittel‐Kasuya‐Yosida theory.

Nuclear Magnetic Resonance in Rare‐Earth—Aluminum Intermetallic Compounds: RAl3

The Knight shifts of the 27Al NMR in LaAl3, CeAl3, PrAl3, NdAl3, GdAl3, and TbAl3 have been measured at temperatures from 78° up to 450°K. The effective exchange constants J between the 4f electrons localized at the rare‐earth ions and the conduction electrons at the Al nuclei have been derived to be −0.2 eV. Ruderman—Kittle—Yosida periodic oscillations of the conduction electron polarization have been used to relate the results with those obtained for RAl2. Nuclear quadrupole coupling constants have been measured to be |e2qQ|=0.8 Mc/sec. On the basis of the ionic point model e2qQ has been calculated for RAl3 and RAl2.

Electrical conduction and19F NMR of solid solutions La1−xBaxF3−x

Abstract The electrical conductivity and19F NMR spin-spin relaxation of single crystals of the anion-deficient solid solutions La1−xBaxF3−x (0 × 0.095) have been investigated. In the temperature dependence of the conductivity a knee is observed, which is ascribed to exchange of fluoride ions between inequivalent sublattices. This is confirmed by spin-spin relaxation in pure LaF3 and the solid solutions. Self-diffusion coefficients derived from the conductivity are in agreement with those from the spin-lattice relaxation time T1ϱ in the rotating frame, indicating an absence of associates (BaLa VF)x above room temperature.

Microwave Rotational Spectrum of Indium Monochloride

With a high‐temperature Stark‐spectrometer the J=4←3 rotational spectrum of 115In35Cl has been observed. Quadrupole hyperfine structure has been observed for the lowest four vibrational states. In an analysis of the spectrum the following constants have been derived: the rotational—vibrational constants Y01, Be, Y11(≈—αe), Y21(≈γe), Y02(≈—De), and Y20(≈—ωexe); the quadrupole coupling constants eqQ including the dependence on the vibrational state; the coefficients a0, a1, and a2 of the internuclear potential; and the internuclear distance re. From the quadrupole hyperfine structure it is concluded that the molecule is 77% ionic, and that the antishielding factor of In+—γ∞≈65.

Two-magnon Raman scattering in the two-dimensional antiferromagnet K2FeF4

Abstract Two-magnon Raman scattering in the planar quadratic antiferromagnet K2FeF4 is investigated. The temperature dependence of the energy shift is in good agreement with second-order Green-function theory, as is the linewidth at low temperature. Numerical results, including renormalization, are the Heisenberg exchange J k B = −14.5 ± 0.7 K and the anisotropy Δ(T = 0) = gμ B H A 4|J|S = 0.18 ± 0.05 , but with J[1 + Δ(T = 0)] k B = −17.06 ± 0.10 K .

Determination of the g-tensor anisotropy of triclinic DPPH at 4.5 mm wavelength

Abstract The anisotropic part of the spectroscopic splitting tensor g has been determined in a single crystal of triclinic DPPH by means of electron paramagnetic resonance at 4.5 mm wavelength. The method of evaluation of the g -tensor from the experimental data is described. The result after diagonalization is: δg 1 = +0.6 × 10 -4 , δg 2 = = +3.0 × 10 -4 , δg 3 = −3.6 × 10 -4 . The directions of the principal axes of the tensor are given relative to the crystallographic axes. The results are discussed in terms of the spin-orbit coupling.