Crystal field interactions in the chiral compounds RNi3Ga9 (R = Tb, Dy, Ho and Er) studied by inelastic neutron scattering
Loading...
Date
2020-11-11
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Institute of Nuclear Science and Engineering (AINSE)
Abstract
In recent years, compounds with chiral structures have attracted much attention mainly because of noncollinear and non-coplanar spin textures, which have an important application in spintronics. In chiral
compounds, the lack of inversion symmetry can give rise to an asymmetric spin interaction, the so-called
Dzyaloshinskii-Moriya interaction, which contributes to the symmetric exchange interaction and anisotropy
effects from the crystal field. These interactions’ coexistence can result in unusual magnetic properties and
exotic magnetic structures with potential for many applications and novel phenomena. In this work, we
study the magnetic properties of the chiral compounds RN i3Ga9 (R = Tb, Dy, Ho and Er), which crystalize in a trigonal ErNi3Al9-type structure with non-centrosymmetric space group R32 [1]. For this purpose,
we analyzed the inelastic neutron scattering (INS) spectra in powder samples at several temperatures (T) to
study the crystal electric field (CEF) excitations and ground-state. The INS experiments were performed at
the SIKA beamline using the cold triple-axis spectrometer. The spectrum was analyzed at four temperatures
for ErN i3Ga9 (T = 8, 20, 50 and 100K) and two temperatures for T bN i3Ga9 (T = 50 and 100K), HoN i3Ga9
(T = 30 and 100K) and DyN i3Ga9 (T = 50 and 100K). Moreover, transverse and longitudinal magnetic susceptibility was measured in single-crystalline samples to fit the CEF parameters better.
We developed a code based on the magnetic susceptibility and differential cross-section for magnetic scattering
at low Q (dipole approximation) to process and analyze the experimental data. The effective CEF hamiltonian
for the system follows the C3 point symmetry, which results in 9 CEF parameters overall. The least-square
fitting procedure uses a machine-learning algorithm based on particle swarm optimization. We report the
energy levels scheme due to the crystal field and the CEF ground state’s eigenfunctions. In particular, the
INS spectra for the ErNi3Ga9 compound showed peaks associated with the so-called hot transitions, which
take place between excited energy levels. We only observed peaks associated with transitions between the
ground-state and the first excited levels for R = Ho, Tb, and Dy. The calculated INS spectra and magnetic
susceptibility were in good agreement with the experimental data. In particular, the calculated magnetic
susceptibility showed that the direction of easy magnetization occurs along the c-axis for the ErNi3Ga9 compound and along the basal plane for the other compounds. It evidences the oblate and prolate nature of the
rare-earth ions charge distributions. In summary, we used inelastic neutron scattering data to establish the
CEF parameters for all compounds according to the C3 point symmetry. The obtained parameters describe
the CEF energy levels’ configuration and the relative intensity of the peaks observed in the INS spectrum,
besides the transverse and longitudinal magnetic susceptibility in the paramagnetic region.
Description
Keywords
Spin, Anisotropy, Hamiltonians, Magnetization, Neutrons, Scattering, Ground states, Particles, Symmetry, Data
Citation
Gil, L., Lora-Serrano, R., Duque, J. G. S., Garcia, D., Cadogan, S., & Rule, K. (2020). Crystal field interactions in the chiral compounds RNi3Ga9 (R = Tb, Dy, Ho and Er) studied by inelastic neutron scattering. Paper presented to the ANBUG-AINSE Neutron Scattering Symposium, AANSS 2020, Virtual Meeting, 11th - 13th November 2020. (pp. 75). Retrieved from: https://events01.synchrotron.org.au/event/125/attachments/725/1149/AANSS_Abstract_Booklet_Complete_-_1_Page_Reduced.pdf