J1−J2 square lattice antiferromagnetism in the orbitally quenched insulator MoOPO4

Abstract

We report magnetic and thermodynamic properties of a 4d 1 (Mo 5+ ) magnetic insulator MoOPO4 single crystal, which realizes a J1-J2 Heisenberg spin-1/2 model on a stacked square lattice. The specific-heat measurements show a magnetic transition at 16 K which is also confirmed by magnetic susceptibility, ESR, and neutron diffraction measurements. Magnetic entropy deduced from the specific heat corresponds to a two-level degree of freedom per Mo 5+ ion, and the effective moment from the susceptibility corresponds to the spin-only value. Using ab initio quantum chemistry calculations we demonstrate that the Mo 5+ ion hosts a purely spin-1/2 magnetic moment, indicating negligible effects of spin-orbit interaction. The quenched orbital moments originate from the large displacement of Mo ions inside the MoO6 octahedra along the apical direction. The ground state is shown by neutron diffraction to support a collinear Néel-type magnetic order, and a spin-flop transition is observed around an applied magnetic field of 3.5 T. The magnetic phase diagram is reproduced by a mean-field calculation assuming a small easy-axis anisotropy in the exchange interactions. Our results suggest 4d molybdates as an alternative playground to search for model quantum magnets.

Magnetic and structural properties of Ni-substituted magnetoelectric Co4Nb2O9

“…In order to obtain the magnetic part of the specific heat, C mag , one should subtract the lattice contribution. We simulate the lattice contribution from the high-temperature data by taking into account both the Debye (C D ) and Einstein (C E ) contributions, i.e., C lattice = C D + C E [35]. the Supplemental Material [34].…”

Frustration-free spatially anisotropic S=1 square-lattice antiferromagnet Ni[SC(NH2)2Zhao1, Zhao2, Chen3 et al. 2019Phys. Rev. B4110View full textAdd to dashboardCite

“…In the intermediate regions, the system is highly frustrated and novel quantum ground states are emerged, like spin liquid state for J 1 > 0 and spin nematic state for J 1 < 0. This J 1 − J 2 model has been successfully applied to many S = 1/2 compounds [1][2][3][4][5][6][7][8][9][10][11][12][13][14], while analogous study on S = 1 systems has been rarely carried out. Quantum phase diagram of a spatially anisotropic S = 1 square lattice has been established theoretically [15][16][17].…”

Ferrimagnetic 120∘magnetic structure inCu2OSO4

“…We use a combined fit to describe C p and the volume of the unit cell obtained from x-ray diffraction by a phonon (lattice only) model. Similar to what was done in [39,40], the lattice contribution to the specific heat is given by…”