RESUMO
Polar magnetic materials exhibiting appreciable asymmetric exchange interactions can potentially host new topological states of matter such as vortex-like spin textures; however, realizations have been mostly limited to half-integer spins due to rare numbers of integer spin systems with broken spatial inversion lattice symmetries. Here, we studied the structure and magnetic properties of the S = 1 integer spin polar magnet ß-Ni(IO3)2 (Ni2+, d8, 3F). We synthesized single crystals and bulk polycrystalline samples of ß-Ni(IO3)2 by combining low-temperature chemistry techniques and thermal analysis and characterized its crystal structure and physical properties. Single crystal X-ray and powder X-ray diffraction measurements demonstrated that ß-Ni(IO3)2 crystallizes in the noncentrosymmetric polar monoclinic structure with space group P21. The combination of the macroscopic electric polarization driven by the coalignment of the (IO3)- trigonal pyramids along the b axis and the S = 1 state of the Ni2+ cation was chosen to investigate integer spin and lattice dynamics in magnetism. The effective magnetic moment of Ni2+ was extracted from magnetization measurements to be 3.2(1) µB, confirming the S = 1 integer spin state of Ni2+ with some orbital contribution. ß-Ni(IO3)2 undergoes a magnetic ordering at T = 3 K at a low magnetic field, µ0H = 0.1 T; the phase transition, nevertheless, is suppressed at a higher field, µ0H = 3 T. An anomaly resembling a phase transition is observed at T ≈ 2.7 K in the Cp/T vs. T plot, which is the approximate temperature of the magnetic phase transition of the material, indicating that the transition is magnetically driven. This work offers a useful route for exploring integer spin noncentrosymmetric materials, broadening the phase space of polar magnet candidates, which can harbor new topological spin physics.
RESUMO
Excellent nonlinear optical materials simultaneously meet the requirements of large SHG response, phase-matching capability, wide transparency windows, considerable energy band-gap, good thermal stability and structure stability. Herein, two new promising nonlinear optical (NLO) crystals LiMII (IO3 )3 (MII =Zn and Cd) are rationally designed by the aliovalent substitution strategy from the commercialized α-LiIO3 with the perfect parallel alignment of IO3 groups. Compared with parent α-LiIO3 and related AI 2 MIV (IO3 )6 , the title compounds exhibit more stable covalent 3D structure, and overcome the racemic twinning problem of AI 2 MIV (IO3 )6 . More importantly, both compounds inherit NLO-favorable structure merits of α-LiIO3 and show larger SHG response (≈14× and ≈12×KDP), shorter absorption edge (294 and 297â nm) with wider energy band-gap (4.21 and 4.18â eV), good thermal stability (460 and 430 °C), phase-matching behaviors, wider optical transparency window and good structure stability, achieving an excellent balance of NLO properties.
RESUMO
Semiconductor-based X-ray detectors with low detectable thresholds become critical in medical radiography applications. However, their performance is generally limited by intrinsic defects or unresolved issues of materials, and developing a novel scintillation semiconductor for low-dose X-ray detection is a highly urgent objective. Herein, a high-quality rare-earth iodate Tm(IO3 )3 single crystal grown through low-cost solution processing is reported with a wide bandgap of 4.1 eV and a large atomic number of 53.2. The roles of IO and TmO groups for charge transport in the Tm(IO3 )3 are revealed with the structural difference between the [101] and [ 1 ¯ 01 ] $[{\bar{1}}01]$ crystal orientations. Based on anisotropic responses of material properties and detection performances, it is found that the [ 1 ¯ 01 ${\bar{1}}01$ ] orientation, the path with fewer IO groups, achieves a high resistivity of 1.02 × 1011 Ω cm. Consequently, a single-crystal detector exhibits a low dark current and small baseline drifting due to the wide bandgap, high resistivity and less ion migration of Tm(IO3 )3 , resulting in a low detection limit of 85.2 nGyair s-1 . An excellent X-ray imaging performance with a high sensitivity of 4406.6 µC Gyair -1 cm-2 is also shown in the Tm(IO3 )3 device. These findings provide a new material design perspective for high-performance X-ray imaging applications.