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.

We have investigated the superconducting properties of the noncentrosymmetric superconductor LaRhSi 3 by performing magnetization, specific heat, electrical resistivity and muon spin relaxation (µSR) measurements. LaRhSi 3 crystallizes with the BaNiSn 3 -type tetragonal structure (space group I4 mm) as confirmed through our neutron diffraction study. Magnetic susceptibility, electrical resistivity and specific heat data reveal a sharp and well defined superconducting transition at T c = 2.16 ± 0.08 K. The low temperature specific heat data reveal that LaRhSi 3 is a weakly coupled bulk BCS superconductor and has an s-wave singlet ground state with an isotropic energy gap of ∼ 0.3 meV, 2∆ 0 /k B T c = 3.24. The specific heat data measured in applied magnetic field strongly indicate a type-I behaviour. Type-I superconductivity in this compound is also inferred from the Ginzburg-Landau parameter, κ = 0.25. Various superconducting parameters, including the electron-phonon coupling strength, penetration depth and coherence length, characterize LaRhSi 3 as a moderate dirty-limit superconductor. A detailed study of the magnetic field-temperature (H − T ) phase diagram is presented and from a consideration of the free energy, the thermodynamic critical field, H c0 is estimated to be 17.1 ± 0.1 mT, which is in very good agreement with that estimated from the transverse field µSR measurement that gives H c0 = 17.2 ± 0.1 mT. The transverse field µSR results are consistent with conventional type-I superconductivity in this compound. Further, the zero-field µSR results indicate that time reversal symmetry is preserved when entering the superconducting state, also supporting a singlet pairing superconducting ground state in LaRhSi 3 .

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Dimensionality is one of the most important parameters of physical phenomena. Only two things determine the universality class of a phase transition: the dimensionality of a given system and the symmetry of the order parameter. In most cases, the dimensionality of a substance is predetermined by its crystal structure. Examples in which the effective dimensionality is reduced are quite rare. Here we show that the three-dimensional cubic system of Tl(2)Ru(2)O(7) most probably evolves into a one-dimensional spin-one Haldane system with a spin gap below 120 K, accompanied by anomalies in the structure, resistivity and susceptibility. We argue that these anomalies are due to an orbital ordering of Ru 4d electrons, with a strong coupling among three degrees of freedom: orbital, spin and lattice. Our work provides a unique example of the spontaneous formation of Haldane system with an insight into the intriguing interplay of different degrees of freedom.