Magnetic structure of paramagnetic MnO

Abstract

Using a combination of single-crystal neutron scattering and reverse Monte Carlo refinements, we study the magnetic structure of paramagnetic MnO at a temperature (160 K) substantially below the Curie-Weiss temperature |θ| ∼ 550 K. The microscopic picture we develop reveals a locally-ordered domain structure that persists over distances many times larger than the correlation length implied by direct analysis of the spin correlation function. Moreover, the directional dependence of paramagnetic spin correlations in paramagnetic MnO differs in some important respects from that of its incipient ordered antiferromagnetic state. Our results have implications for the understanding of paramagnetic states in weakly-frustrated systems, including hightemperature superconductors.

Magnetic Excitations of the Classical Spin Liquid MgCr2O4

“…Our choice of a Heisenberg model is motivated by the small orbital contribution to the magnetic moment (g ≈ 2.05) and ESR results above T N [36,37]. This is verified by a preliminary reverse Monte Carlo analysis [38][39][40][41] that reveals an isotropic distribution of spin orientations [see Sec. S3].…”

Total scattering and the pair distribution function in crystallography

“…The magnetic total scattering formalism, in terms of spin-spin correlations, was first set out in 1964 in a paper by Blech and Averbach [127]. They used the Fourier transform of the magnetic total scattering to investigate the likely spin arrangements in MnO above the Néel temperature; local correlations between magnetic moments exist at temperatures well above T N in MnO [128]. This formalism was later incorporated into an RMC code and used to study the magnetic structure of amorphous materials [129].…”

“…This work using RMC led to the development of the program spinvert [135], a dedicated RMC-based program for refining disordered magnetic structures using magnetic diffuse scattering data. This has had considerable success for a wide range of systems using data from powdered [136] and single crystal samples [128]. Although spinvert does not strictly use magnetic total scattering, when applied to disordered systems it effectively is as the magnetic Bragg component is zero.…”

Magnetic excitations of the classical spin liquid MgCr2O4

“…We will show that it is crucial to model the two inequivalent third-neighbor pathways J 3a and J 3b separately. Our choice of a Heisenberg model is motivated by the small orbital contribution to the magnetic moment (g ≈ 2.05) and a preliminary reverse Monte Carlo analysis [34][35][36][37] that revealed an isotropic distribution of spin orientations [see Sec. S3].…”