Unconventional magnetic order in the frustrated diamond-lattice antiferromagnetCoAl2O4studied by neutron diffraction and classical Monte Carlo simulation

Abstract

CoAl 2 O 4 spinel with magnetic Co 2+ ions on the diamond lattice is known to be magnetically frustrated. We compare neutron single-crystal diffraction patterns measured in zero and applied magnetic fields with the ones obtained from classical Monte Carlo models. In simulations we test the influence of various parameters on diffraction patterns: the ratio of nearest-, J 1 , and next-nearest-, J 2 , neighbor interactions, magnetic field applied along the principal crystallographic directions, and random disorder on the A(Co 2+ ) and B(Al 3+ ) sites. We conclude that the models considered so far explain the broadening of magnetic Bragg peaks in zero magnetic field and their anisotropic response to applied magnetic field only partly. As bulk properties of our single crystal are isotropic, we suggest that its microstructure, specifically 111 -twin boundaries, could be a reason for the nonconventional magnetic order in CoAl 2 O 4 .

Ground state and low-energy magnetic dynamics in the frustrated magnetCoAl2O4as revealed by local spin probes

“…Bulk magnetic measurements agree very well with the polycrystalline results in Ref. [11] for the same x, classifying this sample to the spin liquid regime [13]. NS data were interpreted in terms of the occurrence of spiral spin liquid correlations at elevated temperatures and of an unconventional static shortrange collinear AFM order emerging below a characteristic temperature T * = 8 K [9].…”

“…For our study we have chosen a single crystal of CoAl 2 O 4 with the inversion parameter x ≈ 8%. Part of this crystal was studied before by neutron scattering (NS) and thermodynamic techniques [9,13]. Bulk magnetic measurements agree very well with the polycrystalline results in Ref.…”

“…The CoAl 2 O 4 single crystal with x ≈ 8% [9,13] was grown and primarily characterized in Ref. [16] and then was further investigated by neutron scattering and thermodynamic methods in Refs.…”

“…A substantial spin frustration can nevertheless occur due to a sizable next-nearest-neighbor AFM exchange interaction J 2 compared to the nearest neighbor exchange J 1 . Indeed, several A-site magnetic spinels have been classified as strongly frustrated magnets, among those CoAl 2 O 4 has attracted a lot of attention [6][7][8][9][10][11][12][13].…”

Revisiting the ground state of CoAl2O4 : Comparison to the conventional antiferromagnet MnAl2O

“…The higher level of cation inversion in the MnAl2O4 sample indicates that this novel behavior is primarily an effect of greater next-nearest-neighbor exchange. The A-site spinels, AB 2 X 4 with A magnetic, have seen a surge of interest in the past decade, due to a series of interesting experimental observations [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and theoretical predictions of novel spin-liquid ground states [16][17][18][19][20] . Magnetic cations in these materials comprise a bi-partite diamond lattice, and novel behavior is argued to be the result of a competition between nearest (J 1 ) and nextnearest (J 2 ) neighbor superexchange interactions 2,21 .…”