Magnetic phase transitions in spin-1/2 and spin-1 frustrated triangular lattice antiferromagnets Li2(Cu,Ni)W2O8

Datum

30.08.2016

Zeit

11:00 - 13:00

Sprecher

Prof. Dr. Ramesh Chandra Nath

Zugehörigkeit

School of Physics, IISER, India

Serie

MPI-CPfS Festkörperphysikalisches Kolloquium

Sprache

en

Hauptthema

Chemie

Andere Themen

Physik, Chemie

Host

Dr. M. Baenitz

Beschreibung

Frustrated magnetism is currently a topic of renewed interest because of unusual low-temperature properties revealed by frustrated magnets. An interesting phenomenon in such systems is the formation of quantum spin liquid (QSL) – a strongly correlated ground state lacking long-range magnetic order. QSL originates from quantum fluctuations that are particularly strong in systems with frustrated geometry, reduced dimensionality and low spin value. Theoretical progress in this field has advanced a lot, but experimental research requires appropriate model materials which can be described by simple spin Hamiltonian. Magnetic frustration in three dimension (3D) manifests itself in the newly discovered spin-1/2 and spin-1 insulators Li2(Cu,Ni)W2O8. Thermodynamic measurements along with band structure calculations suggest peculiar spin lattice built of triangular planes with frustrated interplane couplings. Li2CuW2O8 undergoes a magnetic LRO at TN ≈ 3.9 K. Neutron diffraction experiments reveal collinear arrangement of spins below TN with a reduced ordered moment of 0.65 μB. Our thermodynamic measurements are complemented by 7Li NMR experiments that probe the magnetic state incisively and reveal subtle effects associated with frustration. NMR spectra below TN suggest a commensurate spin structure in the ordered state, consistent with the neutron diffraction experiments. The spin-lattice relaxation rate reveals unusual spin dynamics above TN. The dilution of the spin lattice with nonmagnetic Zn atoms has dramatic influence on TN that decreases exponentially similar to quasi-one-dimensional antiferromagnets. On the other hand, Li2NiW2O8 undergoes successive transitions at TN1 ≈ 18 K and TN2 ≈ 12.5 K in zero field. Nuclear magnetic resonance and neutron diffraction experiments reveal collinear and commensurate magnetic order below TN2. Incommensurate magnetic order, presumably of spin-density-wave type, is observed in the region between TN2 and TN1. We show that the collinear magnetic order in Li2NiW2O8 is incompatible with the triangular lattice geometry and thus driven by a pronounced easy-axis single-ion anisotropy.

Links

• MPI CPfS

Letztmalig verändert: 30.08.2016, 09:36:15