The dilute magnetic semiconductor has the dual characteristics of semiconductor materials and magnetic materials, and is one of the candidate materials for solving the problems of the post-Moore era. The National Research Council of the United States pointed out as early as 1991 that dilute magnetic semiconductors have broad application prospects in information communication, processing, and storage. The 125 major scientific issues released on the 125th anniversary of the publication of Science in 2005 include “whether room temperature ferromagnetic semiconductors are availableâ€. (Ga, Mn) As is the representative III-V system and is the most widely studied material in dilute magnetic semiconductors. However, in these materials, the heterogeneous doping of (Ga3 +, Mn2 +) introduces both spin and charge, and the content of Mn is difficult to increase effectively, which not only hinders the increase of the Curie temperature of the material, but also makes it difficult to construct a homogeneous PN junction. Spin and charge "bundle" doping has become the main bottleneck restricting the further development and practicality of III-V systems such as (Ga, Mn) As. The research team led by Jin Changqing, Institute of Physics, Chinese Academy of Sciences / Beijing National Research Center for Condensed Matter Physics, discovered new dilute magnetic semiconductors Li (Zn, Mn) As and Li (Zn, Mn) As separated in 2011 from charge and spin doping In (Zn2 +, Mn2 +) equivalent magnetic elements are used instead of introducing spin, the excessive doping of the non-magnetic element Li introduces charges, thereby achieving the separation of charge and spin doping mechanisms [Nature Communications 2, 422 (2011)]. Along with this material design idea, they further extended the material system to a layered structure and discovered (Ba, K) (Zn, Mn) 2As2 (abbreviated as BZA) dilute magnetic semiconductor with Curie temperature up to 230K, refreshing this class The highest record of controllable Curie temperature in dilute magnetic semiconductors [Nature Communications 4, 1442 (2013), Chinese Science Bulletin 59, 2524 (2014)]. They then grew the BZA single crystal, and collaborated with Li Yongqing's research group to prepare an Andrév junction based on the BZA single crystal [Scientific Reports 7, 14473 (2017)]. In order to explore effective ways to increase the Curie temperature of BZA, they used the neutron partition function technique (PDF) to study the local magnetic structure of BZA, and found that the nearest neighbor Mn ion in the material still has a short-range ferromagnetic sequence at room temperature. The results show that it is highly possible to achieve room temperature ferromagnetism on BZA through material process optimization [Physical Review B 94, 94102 (2016)]. Pressure can change the energy band width of the dilute magnetic semiconductor, thereby changing the carrier characteristics, enhancing the ferromagnetic exchange effect, and then adjusting the Curie temperature of the material. They used a diamond anvil combined with X-ray magnetic circular dichroism (XMCD) and other spectroscopy techniques to confirm the effective regulation of physical external pressure on BZA ferromagnetism. The research results further showed that the cell volume was compressed without causing lattice distortion , Will further increase BZA Curie temperature [Physical Review B 95, 94412 (2017)]. Chemical pressure, that is, doping the material with ions of different sizes in equivalent states, without introducing charge doping, induces a change in the unit cell volume of the material. Like physical external pressure, chemical pressure can effectively control the physical properties of materials, which is especially suitable for isotropic compounds. Jin Changqing's associate researcher Deng Zheng and graduate student Yu Shuang recently used the same valence of Sr and Ca ions to replace the new dilute magnetic semiconductor (Sr, Na) (Cd, Mn) 2As2 with good isotropic compression characteristics that they discovered before Journal of Applied Physics 120, 83902 (2016)] conducted chemical pressure control and successfully developed (Ca, Na) (Cd, Mn) 2As2 dilute magnetic semiconductor new materials. Compared with (Sr, Na) (Cd, Mn) 2As2, the ferromagnetism of (Ca, Na) (Cd, Mn) 2As2 is effectively enhanced. Figure 1 shows the crystal structures of (Ca, Na) (Cd, Mn) 2As2 and (Sr, Na) (Cd, Mn) 2As2. They have the same structure and belong to the hexagonal crystal system. Compared to (Sr, Na) (Cd, Mn) 2As2, the unit cell volume of (Ca, Na) (Cd, Mn) 2As2 is reduced by 6%, which indicates that the replacement of large-size Sr with Ca of small size does introduce Chemical pressure. Figure 2 is the curve of the magnetic susceptibility of (Ca, Na) (Cd, Mn) 2As2 with temperature. The maximum Curie temperature is increased by about 50% relative to (Sr, Na) (Cd, Mn) 2As2. Moreover, the saturation magnetic moment of (Ca, Na) (Cd, Mn) 2As2 reaches 3 μB / Mn, which is 3 times that of (Sr, Na) (Cd, Mn) 2As2. These results indicate that chemical pressure plays a crucial role in the (Sr, Na) (Cd, Mn) 2As2- (Ca, Na) (Cd, Mn) 2As2 system, and effectively enhances the ferromagnetic correlation and improves the里 温度。 Li temperature. Figure 3 shows the Hall resistance of (Ca, Na) (Cd, Mn) 2As2 at 2K and 300K. The Curie temperature shows a significant anomalous Hall effect, which proves the intrinsic ferromagnetic properties of the material. The energy band computing part of this work was completed in cooperation with Professor Li Zhi of Nanjing University of Science and Technology. This work clarified the prospect of optimizing the performance of dilute magnetic semiconductor materials through chemical pressure, and the relevant results were published in the recent APL Materials 7, 101119 (2019). The project was supported by the Ministry of Science and Technology (project numbers 2017YFB0405703, 2018YFA03057001) and the National Natural Science Foundation of China (project number 11534016). Silicone bowl / Funnel,High Quality Silicone bowl / Funnel,Silicone bowl / Funnel Details, CN Yangjiang YJCB Trade Co., Ltd , https://www.cbprokitchen.com
Figure 1. Crystal structure of (Ca, Na) (Cd, Mn) 2As2 and (Sr, Na) (Cd, Mn) 2As2, space group P-3m1 
Figure 2. (Ca, Na) (Cd, Mn) 2As2 magnetic susceptibility curve with temperature, the paramagnetic part of the figure shows the Curie fit 
Figure 3. Hall resistance of (Ca, Na) (Cd, Mn) 2As2, the illustration is a partially enlarged view of the abnormal Hall effect at 2K