Study Of Magnetic Excitations Research Articles

Dynamic Spin Phenomena in Complex Structures Based on Ferromagnetic Metals and Semiconductors (Scientific Summary)

A brief review of theoretical and experimental studies of spin phenomena in various hybrid structures based on magnetically ordered metals and semiconductors is presented. In particular, the following issues are addressed: (i) the effects of electrically driven switching of the magnetization with the minimum energy loss; (ii) ferromagnetic ordering in Mn-doped GaAs-AlGaAs quantum wells, which is stimulated by filling the upper Hubbard band; (iii) the analytical and numerical studies of magnetic excitations in nanocomposites formed by ferromagnetic granules; (iv) theoretical studies of spin effects in strongly disordered semiconductor structures; and (v) isotropic magnetoresistance linear in the magnetic field, experimentally observed in GaAs-AlGaAs doped quantum wells, which is attributed to some ordering in the system of localized spins.

Topological hardcore bosons on the honeycomb lattice

This paper presents a connection between the topological properties of hardcore bosons and that of magnons in quantum spin magnets. We utilize the Haldane-like hardcore bosons on the honeycomb lattice as an example. We show that this system maps to a spin-1/2 quantum XY model with a next-nearest-neighbour Dzyaloshinsky–Moriya interaction. We obtain the magnon excitations of the quantum spin model and compute the edge states, Berry curvature, and thermal and spin Nernst conductivities. Because of the mapping from spin variables to bosons, the hardcore bosons possess the same nontrivial topological properties as those in quantum spin systems. These results are important in the study of magnetic excitations in quantum magnets and they are also useful for understanding the control of ultracold bosonic quantum gases in honeycomb optical lattices, which is experimentally accessible.

Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4

We report on high-field electron spin resonance (ESR) studies of magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4. Frequency-field diagrams of ESR excitations are measured for different orientations of magnetic fields up to 25 T. We show that the substantial zero-field energy gap, K, observed in the low-temperature excitation spectrum of Cs2CuBr4, (Zvyagin et al 2014 Phys. Rev. Lett.112 077206) is present well above TN. Noticeably, the transition into the long-range magnetically ordered phase does not significantly affect the size of the gap, suggesting that even below TN the high-energy spin dynamics in Cs2CuBr4 is determined by short-range-order spin correlations. The experimental data are compared with results of model spin-wave-theory calculations for spin-1/2 triangular-lattice antiferromagnet.

Bimagnon studies in cuprates with resonant inelastic x-ray scattering at the OKedge. I. Assessment on La2CuO4and comparison with the excitation at CuL3and CuKedges

We assess the capabilities of magnetic Resonant Inelastic X-ray Scattering (RIXS) at the O $K$ edge in undoped cuprates by taking La_{2}CuO_{4} as a benchmark case, based on a series of RIXS measurements that we present here. By combining the experimental results with basic theory we point out the fingerprints of bimagnon in the O $K$ edge RIXS spectra. These are a dominant peak around 450 meV, the almost complete absence of dispersion both with $\pi$ and $\sigma$ polarization and the almost constant intensity vs. the transferred momentum with $\sigma$ polarization. This behavior is quite different from Cu $L_3$ edge RIXS giving a strongly dispersing bimagnon tending to zero at the center of the Brillouin zone. This is clearly shown by RIXS measurements at the Cu $L_3$ edge that we present. The Cu $L_3$ bimagnon spectra and those at Cu $K$ edge - both from the literature and from our data - however, have the same shape. These similarities and differences are understood in terms of different sampling of the bimagnon continuum. This panorama points out the unique possibilities offered by O $K$ RIXS in the study of magnetic excitations in cuprates near the center of the BZ.

Magnetic excitations in FCC Mn (37%Fe, 3%Cu) alloy

Within the program of our systematic studies of magnetic excitations of manganese alloys the inelastic neutron scattering in FCC Mn(37%Fe,3%Cu) was measured for the temperature range 1.7–600 K. This alloy has the FCC crystal structure both in paramagnetic and AF phase and its composition is close to the range where the enhanced itinerant behaviour was predicted by the theory. The measured spin-wave velocity and the energy gap in the spin wave spectrum were reported earlier to reach the maximum values in this composition range. Our data did not confirm these earlier results. The expected anisotropy of the inelastic neutron scattering was not found neither in the antiferromagnetic phase nor in the paramagnetic one. The q-dependence of the spin-wave damping is quadratic rather than linear and the spin-wave damping increase with temperature, as usually predicted for damping due to magnon scattering on magnons and on other excitations. This result is in contrast with the data for the FCT Mn(10%Fe,3%Cu) where the q-dependence of the spin-wave damping is linear and the damping parameter was found to be temperature independent excepting the region close to TN. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Inelastic neutron scattering study of magnetic excitations in uranium phosphates

Abstract The results of inelastic neutron scattering experiments performed on the compounds U1−xThx(UO2)(PO4)2 (x=0,0.5) and U2O(PO4)2 are presented. The partial substitution of uranium with thorium in the former compound was performed to decouple the magnetic dimers and observe a pure single-ion behaviour. The INS data indicate that the main interaction, responsible for the magnetic excitations observed in all of the compounds examined, is the crystal field due to the oxygen ligand cage that surrounds the U4+ sites, rather than the exchange interaction between magnetic ions.

High-field ESR on quantum spin systems

High-field electron spin resonance (ESR) experiments have been performed on quantum spin systems. A distinct field-induced crossover between the gap-less spinon regime and the gapped sine-Gordon regime is observed for the Heisenberg quantum spin chain; CuBenzoate. In a Shastry and Sutherland model compound SrCu 2(BO 3) 2, a set of multiple-triplet excitations has been resolved by utilizing high-resolution ESR. The splitting of the two-triplet bound state into a few discrete energy levels is considered as the evidence of the extreme localization of the triplet excitations in this compound. The present results indicate the unique and powerful features of ESR in the study of magnetic excitations.

SPIN WAVES IN ANTIFERROMAGNETIC FCT γ-Mn-Ge ALLOYS

Our earlier studies of magnetic excitations in γ-Mn-Fe, γ-Mn-Ni and γ-Mn-Cu alloys are now extended to the Mn-Ge system. At very low concentrations of Ge (5% and 10% Ge) we expected to achieve a reliable extrapolation to pure γ-Mn which cannot be obtained in the single-crystalline form.

Neutron Scattering Study of Magnetic Excitations in a One-Dimensional Heisenberg Antiferromagnet CsVCl3

We report a high energy-resolution neutron scattering study of magnetic excitations in a one-dimensional Heisenberg antiferromagnet CsVCl 3 with S =3/2. Because of the weak antiferromagnetic coupling J '/ J ∼10 -4 in the hexagonal basal plane, the spin direction rotates by 120° with respect to the nearest neighbor spins, and the spin-wave dispersion in the basal plane consists of three branches. In the present experiment we observed an almost dispersionless mode and an acoustic branch in neutron profiles which are in good agreement with the previous studies. Accurate absolute cross-section measurements revealed, however, that the intensity of the acoustic branch could be accounted for neither by the linear spin-wave theory (the observed intensity is weaker by a factor 33) nor by the magneto-vibrational scattering (stronger by two orders of magnitude). Quantum effects, which cause large corrections in quasi-one dimensional antiferromagnets, are also discussed on the basis of the 1/ S expansion, but also fa...

Magnetic excitations in HoZn near the spin rotation temperature

The authors have extended the study of magnetic excitations in the ferromagnet HoZn near its spin rotation temperature. New excitation branches are observed, arising from the coupling between excited levels. A satisfactory description is obtained by taking into account, besides the crystal field and Heisenberg Hamiltonian, second-order magneto-elastic terms or quadrupolar couplings in the single-ion Hamiltonian. Higher-order exchange has little influence on the dispersion curve. The results are in agreement with magnetostatic data.

Rapid inverting of the polarization of a neutron beam using large amplitude oscillating magnetic fields

During the course of designing and constructing a pulsed-neutron-polarization-inverter (PNPI) to be used in the study of magnetic excitations in solids, it was necessary to re-examine the oscillating field method of magnetic resonance in the region where the amplitude of the rf field B 1 is comparable to the dc field B 0. It is found that the phase of the rf field at the instant the neutron enters the spatial region of the field becomes an increasingly important considerations as B 1 B 0 becomes comparable to 1. Analog and digital computer solutions are given for the equations of motion of the neutron's magnetic moment in the presence of various field configurations important in the construction of a PNPI.