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Register a new userHigh-field spectroscopy of singlet-triplet transitions in the spin-dimer systems Sr3Cr2O8 and Ba3Cr2O8
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Magnetic excitations in the isostructural spin-dimer systems Sr3Cr2O8 and Ba3Cr2O8 are probed by means of high-field electron spin resonance at sub-terahertz frequencies. Three types of magnetic modes were observed. One mode is gapless and corresponds to transitions within excited states, while two other sets of modes are gapped and correspond to transitions from the ground to the first excited states. The selection rules of the gapped modes are analyzed in terms of a dynamical Dzyaloshinskii-Moriya interaction, suggesting the presence of phonon-assisted effects in the low-temperature spin dynamics of Sr3Cr2O8 and Ba3Cr2O8
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We present neutron diffraction, magnetic susceptibility and specific heat data for a single-crystal sample of the cubic (Cu3Au structure) compound Pr3In. This compound is believed to have a singlet (Gamma1) groundstate and a low-lying triplet (Gamma4) excited state. In addition, nearest-neighbor antiferromagnetic interactions are frustrated in this structure. Antiferromagnetic order occurs below T_N = 12K with propagation vector (0, 0, 0.5 +/-delta) where delta approx 1/12. The neutron diffraction results can be approximated with the following model: ferromagnetic sheets from each of the three Pr sites alternate in sign along the propagation direction with a twelve-unit-cell square-wave modulation. The three moments of the unit cell of 1 mu_B magnitude are aligned so as to sum to zero as expected for nearest-neighbor antiferromagnetic interactions on a triangle. The magnetic susceptibility indicates that in addition to the antiferromagnetic transition at 12K, there is a transition near 70K below which there is a small (0.005 mu_B) ferromagnetic moment. There is considerable field and sample dependence to these transitions. The specific heat data show almost no anomaly at TN = 12K. This may be a consequence of the induced moment in the Gamma1 singlet, but may also be a sample-dependent effect.
Within the framework of periodic asymmetric Anderson model for Kondo isoulators an effective singlet-triplet Hamiltonian with indirect antiferromagnetic f-f exchange interaction is introduced which allows to study analytically the dynamic magnetic susceptibilities of f-electrons. The approach allows to describe the three-level spin excitation spectrum with a specific dispersion in $YbB_{12}$. Distinctive feature of the consideration is the introduction of small radius singlet and triplet collective f-d excitations which at movement on a lattice form low - and high-energy spin bands.
Momentum-transfer (q) dependent non-resonant inelastic x-ray scattering measurements were made at the N4,5 edges for several rare earth compounds. With increasing q, giant dipole resonances diminish, to be replaced by strong multiplet lines at lower energy transfer. These multiplets result from two different orders of multipole scattering and are distinct for systems with simple 4f^0 and 4f^1 initial states. A many-body theoretical treatment of the multiplets agrees well with the experimental data on ionic La and Ce phosphate reference compounds. Comparing measurements on CeO2 and CeRh3 to the theory and the phosphates indicates sensitivity to hybridization as observed by a broadening of 4f^0-related multiplet features. We expect such strong, nondipole features to be generic for NIXS from f-electron systems.
We present results of magnetisation and electron paramagnetic resonance experiments on the spin-dimer system BaCuSi2O6. Evidence indicates that the origin of anisotropic terms in the spin Hamiltonian is from magnetic dipolar interactions. Axial symmetry-breaking is on a very small energy scale of ~11 mK, confirming Bose Einstein condensation critical scaling over an extended temperature range in the vicinity of the quantum critical point.
We present magnetization and magnetostriction studies of the insulating perovskite LaCoO3 in magnetic fields approaching 100 T. In marked contrast with expectations from single-ion models, the data reveal two distinct first-order spin transitions and well-defined magnetization plateaux. The magnetization at the higher plateau is only about half the saturation value expected for spin-1 Co3+ ions. These findings strongly suggest collective behavior induced by strong interactions between different electronic -- and therefore spin -- configurations of Co3+ ions. We propose a model of these interactions that predicts crystalline spin textures and a cascade of four magnetic phase transitions at high fields, of which the first two account for the experimental data.
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