Ferrimagnetic 120∘^\circ magnetic structure in Cu2OSO4

We report magnetic properties of a 3d$^9$ (Cu$^{2+}$) magnetic insulator Cu2OSO4 measured on both powder and single crystal. The magnetic atoms of this compound form layers, whose geometry can be described either as a system of chains coupled through dimers or as a Kagom\'e lattice where every 3rd spin is replaced by a dimer. Specific heat and DC-susceptibility show a magnetic transition at 20 K, which is also confirmed by neutron scattering. Magnetic entropy extracted from the specific heat data is consistent with a $S=1/2$ degree of freedom per Cu$^{2+}$, and so is the effective moment extracted from DC-susceptibility. The ground state has been identified by means of neutron diffraction on both powder and single crystal and corresponds to a $\sim120$ degree spin structure in which ferromagnetic intra-dimer alignment results in a net ferrimagnetic moment. No evidence is found for a change in lattice symmetry down to 2 K. Our results suggest that \sample \ represents a new type of model lattice with frustrated interactions where interplay between magnetic order, thermal and quantum fluctuations can be explored.Comment: Published in Physical Review

Design and performance of the multiplexing spectrometer CAMEA

The cold neutron multiplexing secondary spectrometer CAMEA (Continuous Angle Multiple Energy Analysis) was commissioned at the Swiss spallation neutron source SINQ at the Paul Scherrer Institut at the end of 2018. The spectrometer is optimised for an efficient data collection in the horizontal scattering plane, allowing for detailed and rapid mapping of excitations under extreme conditions. The novel design consists of consecutive, upward scattering analyzer arcs underneath an array of position sensitive detectors mounted inside a low permeability stainless-steel vacuum vessel. The construction of the world's first continuous angle multiple energy analysis instrument required novel solutions to many technical challenges, including analyzer mounting, vacuum connectors, and instrument movement. These were solved by extensive prototype experiments and in-house developments. Here we present a technical overview of the spectrometer describing in detail the engineering solutions and present our first experimental data taken during the commissioning. Our results demonstrate the tremendous gains in data collection rate for this novel type of spectrometer design

Magnetic Field Induced Quantum Spin Liquid in the Two Coupled Trillium Lattices of K2 Ni2 (SO4)3

Quantum spin liquids are exotic states of matter that form when strongly frustrated magnetic interactions induce a highly entangled quantum paramagnet far below the energy scale of the magnetic interactions. Three-dimensional cases are especially challenging due to the significant reduction of the influence of quantum fluctuations. Here, we report the magnetic characterization of K2Ni2(SO4)3 forming a three-dimensional network of Ni2+ spins. Using density functional theory calculations, we show that this network consists of two interconnected spin-1 trillium lattices. In the absence of a magnetic field, magnetization, specific heat, neutron scattering, and muon spin relaxation experiments demonstrate a highly correlated and dynamic state, coexisting with a peculiar, very small static component exhibiting a strongly renormalized moment. A magnetic field B≳4  T diminishes the ordered component and drives the system into a pure quantum spin liquid state. This shows that a system of interconnected S=1 trillium lattices exhibits a significantly elevated level of geometrical frustration

Magnetic and structural properties of Ni-substituted magnetoelectric Co4Nb2O9

The magnetic and structural properties of polycrystalline Co4-xNixNb2O9 (x = 1, 2) have been investigated by neutron powder diffraction, magnetization and heat capacity measurements, and density functional theory (DFT) calculations. For x = 1, the compound crystallizes in the trigonal P (3) over bar c1 space group. Below T-N = 31 K it develops a weakly noncollinear antiferromagnetic structure with magnetic moments in the ab plane. The compound with x = 2 has crystal structure of the orthorhombic Pbcn space group and shows a hard ferrimagnetic behavior below T-C = 47 K. For this compound a weakly noncollinear ferrimagnetic structure with two possible configurations in the ab plane was derived from neutron diffraction study. By calculating magnetic anisotropy energy via DFT, the ground-state magnetic configuration was determined for this compound. The heat capacity study in magnetic fields up to 140 kOe provides further information on the magnetic structure of the compounds

Spin dynamics in the square-lattice cupola system Ba ( TiO ) Cu 4 ( PO 4 ) 4

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Magnetic Field Induced Quantum Spin Liquid in the Two Coupled Trillium Lattices of K2_2Ni2_2(SO4_4)3_3

Quantum spin liquids are exotic states of matter that form when strongly frustrated magnetic interactions induce a highly entangled quantum paramagnet far below the energy scale of the magnetic interactions. Three-dimensional cases are especially challenging due to the significant reduction of the influence of quantum fluctuations. Here, we report the magnetic characterization of K2Ni2(SO4)3 forming a three-dimensional network of Ni2+ spins. Using density functional theory calculations, we show that this network consists of two interconnected spin-1 trillium lattices. In the absence of a magnetic field, magnetization, specific heat, neutron scattering, and muon spin relaxation experiments demonstrate a highly correlated and dynamic state, coexisting with a peculiar, very small static component exhibiting a strongly renormalized moment. A magnetic field B≳4  T diminishes the ordered component and drives the system into a pure quantum spin liquid state. This shows that a system of interconnected S=1 trillium lattices exhibits a significantly elevated level of geometrical frustration