Spin reorientation in easy-plane kagome ferromagnet Li_9Cr_3(P_2O_7)_3(PO_4)_2

We report the successful growth and characterization of Li_9Cr_3(P_2O_7)_3(PO_4)_2single crystal,and investigate its magnetic properties under external magnetic fields via magnetization and heat capacity measurements.Our study reveals that Li_9Cr_3(P_2O_7)_3(PO_4)_2 is an easy-plane kagome ferromagnet with S=3/2,as evidenced by the Curie–Weiss temperature of 6 K which implies a ferromagnetic exchange coupling in the material.Under zero magnetic field,Li_9Cr_3(P_2O_7)_3(PO_4)_2 undergoes a magnetic transition at TC=2.7 K from a paramagnetic state to a ferromagnetically ordered state with the magnetic moment lying in the kagome plane.By applying a c-axis directional magnetic field to rotate the spin alignment from the kagome plane to the c-axis,we observe a reduction in the magnetic transition temperature as the field is increased.We construct a magnetic phase diagram as a function of temperature and magnetic field applied parallel to the c-axis of Li_9Cr_3(P_2O_7)_3(PO_4)_2 and find that the phase boundary is linear over a certain temperature range.Regarding that theoretically,the field-induced phase transition of the spin reorientation in the easy-plane ferromagnet can be viewed as the ferromagnetic magnon Bose–Einstein condensation(BEC),the phase boundary scaling of field-induced(B c)magnetic transition in Li_9Cr_3(P_2O_7)_3(PO_4)_2 can be described as the quasi-2D magnon BEC,which has been observed in other ferromagnetic materials such as K_2CuF_4.

Analytic solutions for generalized PT-symmetric Rabi models

We theoretically investigate the exact solutions for generalized parity–time(PT)-reversal-symmetric Rabi models driven by external fields with monochromatic periodic, linear, and parabolic forms, respectively. The corresponding exact solutions are presented in terms of the confluent Heun equations without any approximation. In principle, the analytic solutions derived here are valid in the whole parameter space. Such a kind of study may offer potential coherent control schemes of the PT-symmetric two-level systems.

In-situ observation of solid-liquid interface transition during directional solidification of Al-Zn alloy via X-ray imaging

The morphological instability of solid/liquid(S/L)interface during solidification will result in different patterns of microstructure.In this study,two dimension(2 D)and three dimension(3 D)in-situ observation of solid/liquid interfacial morphology transition in Al-Zn alloy during directional solidification were performed via X-ray imaging.Under a condition of increasing temperature gradient(G),the interface transition from dendritic pattern to cellular pattern,and then to planar growth with perturbation was captured.The effect of solidification parameter(the ratio of temperature gradient and growth velocity(v),G/v)on morphological instabilities was investigated and the experimental results were compared to classical"constitutional supercooling"theory.The results indicate that 2 D and 3 D evolution process of S/L interface morphology under the same thermal condition are different.It seems that the S/L interface in 2 D observation is easier to achieve planar growth than that in 3 D,implying higher S/L interface stability in 2 D thin plate samples.This can be explained as the restricted liquid flow under 2 D solidification which is beneficial to S/L interface stability.The in-situ observation in present study can provide coherent dataset for microstructural formation investigation and related model validation during solidification.

Three dimensional dendritic morphology and orientation transition induced by high static magnetic field in directionally solidified Al-10wt.%Zn alloy

Effect of high static magnetic field on the dendritic morphology and growth direction in directionally solidified Al-10 wt.%Zn alloy were studied by three-dimensional(3D) X-ray micro-computed tomography, Electron Back-scattered Diffraction(EBSD) and X-ray Diffraction(XRD). The application of high static axial magnetic field(5T) during directional solidification was found to destabilize the solid/liquid interface and cause the growth direction of dendrite deviate from thermal gradient, leading to irregular solid/liquid interfacial shape and cellular to dendritic morphology transition. The thermoelectric magnetic convection(TEMC) caused by the interaction of thermoelectric effect and magnetic field was supposed to be responsible for the transition. In addition, the EBSD and XRD results confirm that the preferred growth direction of α-Al was found to transform from the traditionally expected <100> to<110>. The dendrite orientation transition(DOT) in Al-10 wt.%Zn alloy can be attributed to the effect of applied magnetic field on the anisotropy of crystal during solidification. The result indicates the potential application of high static magnetic field in altering the morphology and preferred growth direction of dendrite during directional solidification.