Magnetic ordering and spin-liquid state ofYMnO3

Abstract

We have measured the bulk properties as well as the elastic and inelastic neutron scattering of YMnO 3 in order to understand the static and dynamic properties of the Mn moments. Our measurements clearly show that above T N there are short range correlations between spins at the nearest neighbor and next nearest neighbor Mn sites, which also fluctuate in time. This, together with other bulk properties, demonstrates the presence of a spin liquid phase above T N arising from the geometrically frustrated Mn moments. Below T N , a well-defined spin wave develops and we can understand the experimentally measured spin wave spectrum in terms of a Heisenberg Hamiltonian with a small easy plane anisotropy. However, even in the ordered phase we have found evidence of short range spin correlations.

spinvert: a program for refinement of paramagnetic diffuse scattering data

“…Most such approaches essentially involve fitting a simple form for the radial spin correlation function to the powder data. In these methods, the connectivity of the crystal structure is not considered; instead, either the magnitude of the spin correlations is fitted for a one-dimensional list of atomic separations (see, e.g., [14,15]), or the diffuse features are fitted to a broad peak-shape function to estimate the spin correlation length (see, e.g., [16]). However, the crystal structure plays no less significant a role in paramagnets than in ordered magnets: indeed, in a paramagnet the crystal structure completely determines the symmetry and periodicity of the diffuse scattering pattern [17].…”

Elastic anomalies associated with structural and magnetic phase transitions in single crystal hexagonal YMnO3

“…The square of the order parameter calculated from the Brillouin function for an S = 2 system does not provide a good description of the ordering, however. The character of the transition is complicated by the geometrical frustration and evidence for significant spin fluctuations [3,40,53], but both the strain evolution and Figure 8. The strains e 1 , e 2 and e v as a function of temperature, calculated from lattice parameter data from Lee et al [35] using equation (1), shown against I 100 from Chatterji et al [13], with all data scaled to vary between 0 at T N and 1 at 0 K, as well as the square of the Brillouin function for an S = 2 system.…”

The Magnetic Phase Transition and Universality Class of h-YMnO3 and h-(Y0.98Eu0.02)MnO3 Under Zero and Applied Pressure

“…The ordered moment decreases from 3.27 µ B at zero pressure to 1.52 µ B at 5 GPa. Kozlenko et al [14] and earlier, Park et al [31] attributed this to the concurrent existence of a spin liquid phase. This phase is also claimed to be responsible for the lowering of the ordered magnetic moment at zero pressure from the expected 4.0 µ B for (S = 2) Mn 3+ , as well as for the increase in diffuse scattering at the Néel temperature and at the applied pressure.…”