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Magnetostatic mode calculations are presented for bulk and surface spin waves in bilayer cylindrical systems where typically one material is ferromagnetic and the other is anti‐ferromagnetic. The dispersion relations and the localization properties of the modes are shown to be modified compared to previous results for planar bilayers. Numerical examples for the dispersion relations are presented taking the ferromagnet Ni and the uniaxial antiferromagnet GdAlO3 as the two constituents of the cylindrical bilayer. The case where Ni is the core material is shown to give a different behavior from the inverse structure with GdAlO3 as the core.

The changes in the phonon spectrum of NiS at its first‐order transition from itinerant‐electron antiferromagnet to Pauli paramagnet have been studied by triple‐axis and time‐of‐flight neutron techniques.Three of the elastic constants were derived from the initial slopes of the acoustic phonon dispersion relations at five temperatures between 180 and 300 K. C44 and C11 soften discontinuously in the metallic phase, despite the volume decrease. C33 is unchanged within experimental error. The values of these constants are 0.41(3), 2.4(2), and 1.9(2) ×10−12 cgs in the antiferromagnetic semimetal and 0.24(2), 2.0(2), and 1.9(2) ×10−12 cgs in the paramagnetic metal.The weighted density of states was measured in the semimetallic phase at 245°K and in the metallic phase at 269°K. In the low frequency spectrum, the acoustic modes are appreciably lower in the metallic phase than in the semimetallic one, in agreement with the elastic constants data. Furthermore a sharp drop near 25 meV in the 245K spectrum is conside...

In Rb2Mn5Ni5F4 the Mn and Ni ions are randomly distributed on a plane square lattice. The exchange energy between neighboring spins is of the Heisenberg form JS↘⋅S↘ with J=7.4 K, 25.7 K and 89 K for pairs of Mn−Mn, Mn−Ni, and Ni−Ni spins. The mean anisotropy field for the Mn and Ni spins is about 0.7% of the exchange field. The spin dynamics studied by inelastic neutron scattering has been described elsewhere (Phys. Rev. B12, 4963, (1975)) and only the results are summarized here. The dynamic susceptibility χ″ (q,ω) exhibitis two well‐defined peaks in frequency ω for a fixed wave‐vector q. The dispersion relations of the two modes shown in fig. 1 are well accounted for in a simple 4‐sublattice model (J. Phys. C, 8, L328 (1975)), and the width of the zone boundary peaks corresponds to the quintet of Ising frequencies of a spin with different configurations of neighboring spins. The results are in good agreement with χ″ (q,ω) as calculated by the CPA method (J. Phys. C, 8, 1889 (1975)) and also with Monte C...

A neutron scattering study of the acoustic phonons in V2O3 has been carried out in the high temperature metallic phase (above 160 K) and in the low temperature antiferromagnetic insulating phase. The dispersion relations for acoustic phonons propagating along selected high symmetry directions in Ti2O3 have also been measured. In V2O3, there appears to be a low‐lying optic mode in the metallic phase which disappears below the metal insulator transition temperature.

Dilute alloys of the heavy rare earths in yttrium are known to possess antiferromagnetic long‐range order. Below the Neel temperatures, Tb, Dy, and Ho alloys exhibit helical structures and the angles between the moments in adjacent planes along the c‐axes saturate at a value of about 50° in the low concentration limit. These facts suggest that the magnetic order in these dilute alloys is determined mainly by the RKKY exchange interaction χ(q), which is proportional to the generalized susceptibility χ(q) for the conduction electrons of yttrium. In order to obtain information about the J(q), the spin‐wave dispersion curve in the c‐direction of Y(10%Tb) has been measured at 4.7°K by means of the coherent inelastic scattering of neutrons. In spite of the low concentration of magnetic atoms well defined neutron groups were observed. The data have been analyzed on the basis of the frozen‐lattice model in which the equations of motion are averaged over randomly distributed sites of the magnetic atoms. The resulting J(q), which may be interpreted to be characteristic of Y, shows a much larger peak at the wave vector of the helical structure than those obtained for pure rare earth metals. The anisotropy constant obtained in the analysis was smaller than that for pure Tb.

Neutron inelastic scattering studies demonstrate that the antiferromagnet FeCO3 is accurately described by the Ising model. Dispersion relations have been determined for the magnetic and lattice excitations along the two high symmetry directions. A spin‐lattice interaction was observed having strength comparable to the exchange interaction. This coupling affects only the degenerate transverse phonon branch in the trigonal direction and one of the two transverse branches in the two‐fold direction. The symmetry‐dependent magnon‐phonon coupling is explained in terms of a lattice perturbation on the crystal field splitting of the orbital states of the Fe2+ ion which are coupled to the spin by the spin‐orbit interaction.

The transverse branch of the phonon dispersion relations of a single‐Q antiferromagnetic Cr sample have been measured near the zone boundary in the [001] direction (around the H symmetry point). The measurements were made with the phonon wave vector q⇒ both parallel and perpendicular to the spin density wave vector Q⇒ at 200°K and 78°K which are above and below the spin flip temperature. All of the measured dispersion curves displayed anomalies similar to those observed in both the paramagnetic (PM) and multi‐Q antiferromagnetic (AFM) phases. The existence of similar anomalies in the PM and single‐Q AFM phases, which are correlated with prominent features of the Fermi surface, suggests that the Fermi surface for the PM and AFM phases are quite similar. However, in the single‐Q measurements differences were observed in the shape of the anomalies for q⇒ parallel and perpendicular to Q⇒ at both temperatures. These directional differences are assumed to arise from the anisotropy of the Fermi surface introduced by the single‐Q spin density wave.