Far infrared antiferromagnetic resonance in FeCl2, FeBr 2 and FeI2

Abstract

2014 Nous avons effectué des expériences de résonance antiferromagnétique dans FeCl2, FeBr2 et FeI2 en utilisant la technique de spectroscopie par transformation de Fourier dans l'infrarouge très lointain. Dans FeCl2 et FeBr2 nos résultats s'interprètent bien dans le modèle à deux sousréseaux avec un paramètre d'anisotropie D = 9,6 K. Dans FeI2 trois pics d'absorption situés à 21,6 ; 29,2 et 32,2 cm-1 ont été attribués à des excitations d'ondes de spin en centre de zone, ce qu'on ne peut comprendre qu'en supposant que FeI2 possède plus de deux sous-réseaux. Nous avons calculé les fréquences de résonance antiferromagnétique dans un modèle simple à quatre sousréseaux, et nous avons déduit les paramètres adaptés à FeI2. Cependant la séparation de 3 cm-1 que l'on observe expérimentalement entre les deux modes de haute fréquence suggère qu'un tel modèle pourrait être trop simple. Abstract. 2014 A far infrared investigation of antiferromagnetic resonance by means of Fouriertransform spectroscopy has been carried out in FeCl2, FeBr2 and FeI2. In FeCl2 and FeBr2 our results are found to agree well with the two-sublattice model with an anisotropy parameter D = 9.6 K. In FeI2 three absorption peaks situated at 21.6 cm-1, 29.2 cm-1, and 32.2 cm-1 have been attributed to excitation of zone-center spin waves, which can be understood only by assuming that FeI2 has more than two sublattices. The AFMR frequencies in a simple four sublattice model have been calculated, and the parameters relevant to FeI2 have been deduced. However the observation of a 3 cm-1 splitting between the two higher modes suggests that such a model may be too simple.

High-Angular Momentum Excitations in Collinear Antiferromagnet FePS3

“…This is because the magnetic anisotropy term in Hamiltonian (eq 2) is even in S z . In contrast, the energies of 1-magnon excitations (3,4), and consequently, also various bound states of 1-magnons located on different lattice sites, always scale with D.…”

“…This implies the separation of branches equal to twice the Larmor frequency or, equivalently, to twice the Zeeman energy, 2E Z = 2gμ B B, with the g factor typically close to the free-electron value (g = 2). The AFMR that follows such a simple rule was observed in the GHz/THz frequency range for many easy-axis antiferromagnets: in iron and manganese dihalides 4,5 or in magnetic oxides, 6−9 to name a few. At present, the AFMR in easy-axis antiferromagnets represents perhaps the most characteristic and easy-to-identify resonance/excitation in magnetic systems and it serves as a direct probe of the exchange coupling between spins and of the single-ion magnetic anisotropy.…”

“…12 The four uniform modes split into two pairs corresponding to the in-phase and out-of-phase oscillations of parallel sublattices in the up−up-down−down magnetic structure of FePS 3 . The two symmetric modes have energies: (3) whereas the antisymmetric modes are (4) In collinear antiferromagnetic structures with a rotation symmetry around the easy axis, magnons have a well-defined quantum numbers S z = ± 1. An applied magnetic field splits every degenerate pair of modes into descending and ascending branches with the bare g-factor, g S,A ≈ 2.15 in FePS 3 .…”

Single-ion magnon bound states in an antiferromagnet with strong uniaxial anisotropy

“…11 When an external magnetic field ͑H͒ is applied along the easy axis at low temperatures, a transition from the antiferromagnetic to ferrimagnetic phase takes place at about 5 T. 12 Several magnetic phases are present before reaching saturation at about 14 T with the saturation moment of 4.4 B /Fe 2ϩ . 13 The magnetic excitation in FeI 2 was studied by farinfrared ͑FIR͒ spectroscopy, 14,15 ESR, 16 and neutron inelastic scattering 17 measurements. Three absorptions were observed at 1 ϭ21.6 cm Ϫ1 , 2 ϭ29.2 cm Ϫ1 , and 3 ϭ32.2 cm Ϫ1 at 1.2 K in the FIR measurement.…”

Observation of single-ion magnon bound states in the metamagnet FeI2

“…11,12 When an external magnetic field (H) is applied along the easy axis at low temperatures, a transition from the antiferromagnetic to ferrimagnetic phase takes place at about 5 T. 12 Several magnetic phases are present before reaching saturation at about 14 T with the saturation moment of 4.4 B /Fe 2ϩ . 13 The magnetic excitation in FeI 2 was studied by farinfrared ͑FIR͒ spectroscopy, 14,15 ESR, 16 and neutron inelastic scattering 17 measurements. Three absorptions were observed at 1 ϭ21.6 cm Ϫ1 , 2 ϭ29.2 cm Ϫ1 , and 3 ϭ32.2 cm Ϫ1 at 1.2 K in the FIR measurement.…”