First neutron Bragg-edge imaging experimental results at CSNS

The neutron Bragg-edge imaging is expected to be a new non-destructive energy-resolved neutron imaging technique for quantitatively two-dimensional or three-dimensional visualizing crystallographic information in a bulk material,which could be benefited from pulsed neutron source.Here we build a Bragg-edge imaging system on the General Purpose Powder Diffractometer at the China Spallation Neutron Source.The residual strain mapping of a bent Q235 ferrite steel sample has been achieved with a spectral resolution of 0.15%by the time-of-flight neutron Bragg-edge imaging on this system.The results show its great potential applications in materials science and engineering.

Magnetic field enhanced thermal conductivity and origin of large thermopower in layered cobaltates

Cobalt oxide,as one of the most fascinating examples of correlated electronic system,exhibits several exotic transport characteristics,such as superconductivity,charge ordering,and topological frustration.In this study,we are reporting the observation of another intriguing transport phenomenon in calcium cobaltates.Specifically,under a large magnetic field of 7 T,we observed an anomalously enhanced thermal conductivity that was accompanied with a largely suppressed thermopower.This observation reveals a hitherto undiscovered correlation between the two transport factors.Within the premise of Heisenberg model,we have shown that the observed experimental results can be explained consistently only if the magnon excitation is taken into account.Our study offers an insight into the puzzling origin of large thermopower observed in layered cobaltates and provides a specific strategy for further optimization of thermopower.

Phase transition regulation and caloric effect

Solid state refrigeration based on caloric effect is regarded as a potential candidate for replacing vapor-compression refrigeration.Numerous methods have been proposed to optimize the refrigeration properties of caloric materials,of which single field tuning as a relatively simple way has been systemically studied.However,single field tuning with few tunable parameters usually obtains an excellent performance in one specific aspect at the cost of worsening the performance in other aspects,like attaining a large caloric effect with narrowing the transition temperature range and introducing hysteresis.Because of the shortcomings of the caloric effect driven by a single field,multifield tuning on multicaloric materials that have a coupling between different ferro-orders came into view.This review mainly focuses on recent studies that apply this method to improve the cooling performance of materials,consisting of enlarging caloric effects,reducing hysteresis losses,adjusting transition temperatures,and widening transition temperature spans,which indicate that further progress can be made in the application of this method.Furthermore,research on the sign of lattice and spin contributions to the magnetocaloric effect found new phonon evolution mechanisms,calling for more attention on multicaloric effects.Other progress including improving cyclability of FeRh alloys by introducing second phases and realizing a large reversible barocaloric effect by hybridizing carbon chains and inorganic groups is described in brief.