Weakly Coupleds=1/2Quantum Spin Singlets inBa3Cr2O8

Abstract

Using single crystal inelastic neutron scattering with and without the application of an external magnetic field and powder neutron diffraction, we have characterized magnetic interactions in Ba3Cr2O8. Even without a field, we found that there exist three singlet-to-triplet excitation modes in the (h, h, l) scattering plane. Our complete analysis shows that the three modes are due to spatially anisotropic interdimer interactions that are induced by lattice distortions of the tetrahedron of oxygens surrounding the Jahn-Teller active Cr5+(3d1). The strong intradimer coupling of J0=2.38(2) meV and weak interdimer interactions (|Jinter|< or =0.52(2) meV) makes Ba3Cr2O8 a good model system for weakly coupled s=1/2 quantum spin dimers.

Crystal growth, structure and magnetic properties of Ca10Cr7O28

“…In these compounds the intra-bilayer interaction which couples the two triangular layers to form the bilayer is the strongest interaction and is antiferromagnetic, as a result the spins are paired into singlets at low temperatures and the ground state is non-magnetic [3]. The magnetic excitations consist of breaking a singlet into a spin-1 triplet which costs a finite amount of energy, the remaining interactions allow the triplet excitations to hop from dimer to dimer giving rise to a gapped dispersive mode [4,5]. A number of interesting physical phenomena have been observed in these materials such as field-induced transition to longrange magnetic order [6] that maps onto Bose-Einstein condensation [7], and strongly correlated behavior of the magnetic excitations at elevated temperature in contrast to the thermally induced decoherence typical of convention magnets [8,9].…”

Infrared phonons and specific heat in the gapped quantum magnet Ba3Cr2O8

“…crystal 5,16 and the low monoclinic symmetry make it difficult to determine the eigenfrequency, damping coefficient and plasma frequency of the phonon modes below the Jahn-Teller transition.…”

“…Fitting to this model resulted in an intra-dimer exchange interaction J 0 = 2.15 meV consistent with the value of 2.38 meV determined by neutron experiments. 5 The detailed magnetic structure has been studied theoretically based on extended Hückel tight binding calculations. 15 The authors of Ref.…”

“…The anomaly at T JT = 70 K is independent on the magnitude of magnetic field, and marks the structural phase transition from hexagonal R3m to monoclinic C 2/c, in agreement with the results obtained from neutron diffraction measurements. 5 The anomaly below 20 K is very sensitive to the magnitude of the magnetic field indicating that is related to the spin degrees of freedom.…”

“…5,16 Thus the modeling here with Lorentzian functions is rather a way to parameterize the reflectivity spectra and reveal clear changes occurring at T JT .…”