Abstract
We report on the intriguing evolution of the dynamical spin correlations of the frustrated spinel ZnMn2O4. Inelastic neutron scattering and magnetization studies reveal that the dynamical correlations at high temperatures are 1D. At lower temperature, these dynamical correlations become 2D. Surprisingly, the dynamical correlations condense into a quasi 2D Ising-like ordered state, making this a rare observation of two dimensional order on the spinel lattice. Remarkably, 3D ordering is not observed down to temperatures as low as 300 mK. This unprecedented dimensional crossover stems from frustrated exchange couplings due to the huge Jahn-Teller distortions around Mn3+ ions on the spinel lattice.
Highlights
Frustrated magnets, in which the magnetic interactions are frustrated by the geometry of the lattice, have been the subject of intense experimental and theoretical study[1,2]
The interactions within a given layer consists of weakly coupled spin chains with a relatively strong intrachain coupling resulting from direct exchange
As the Mn-O octahedra are are connected by edges rather than corners, the dominant interactions will occur through direct exchange between the t 2g orbitals of the Mn ions[15], and should exhibit strong dependence on the Mn-Mn separation distance
Summary
Frustrated magnets, in which the magnetic interactions are frustrated by the geometry of the lattice, have been the subject of intense experimental and theoretical study[1,2]. We demonstrate that geometrical frustration stabilizes low dimensional magnetism in the spinel, ZnMn2O4 In this particular example, the system develops short range 1D dynamical correlations at room temperature. The interactions within a given layer consists of weakly coupled spin chains with a relatively strong intrachain coupling resulting from direct exchange. This can be mapped onto the rectangular Ising model, considered by Onsager[10]. The orbital ordrering partially lifts the frustration of this lattice and allows us a rare opportunity to examine the ground state of uniaxial spins placed on a spinel lattice with anisotropic exchange interactions
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