Study on the annihilation of photodoped positron by giant magnetoresistive material Sf9GdiFeMQ Hu Yanchun 1 Lu Qingfeng 1, Chen Jingdong 2, Zhang Xing 1 Xu Yongguang 1 Zhang Qin 3 (1 School of Physics and Information Engineering, Henan Normal University, Xinxiang 453007, Henan 2 Physics of Xinyang Normal University With the School of Electronic Engineering, Xinyang, Henan 464000, 3 School of Mathematics and Physics, Shandong Jiaotong University, Jinan, Shandong 250300), respectively, they made positron annihilation after 40mn. According to the two-state capture model, the life spectrum consists of two life components: a short life component t and a long life component T. The short life component t reflects the life of the positron obliterated in the Bloch state (free state), I is the intensity, It shows the proportion of the life component; the long life component T reflects the life of the positron annihilated in the defect trapping state. The size of T can give the type of defect; 2 shows the size of the defect concentration in the material. The positron lifetime parameter can also be used in annihilation, and it also includes the contribution of annihilation in small-sized point defects (voids, dislocations, micro-voids, etc.), indicating that there are enough micro-defects (such as single vacancies in unilluminated samples) , Double vacancies, point defects and anti-position defects) capture positrons, and these defects are introduced by the manufacturing process of the sample sr9Gd0i FMo. With the increase of light doping, a large number of micro-defects are combined into vacancy groups, which makes the capture positive The number of electron vacancy groups increases a lot, so the short life increases with the increase of light time. With the continuous increase of light doping (> 20mn), a large number of electron-hole pairs are formed, which greatly reduces the number of holes that capture positrons, and the capture rate Decreased, the annihilation rate increased T decreased.
Due to light irradiation, the point defects are activated, and the defect concentration in the sample is increased; when the illumination time is> 20 msn, continuous illumination causes a large number of electron-hole pairs to be formed, that is, a large number of holes that capture positrons are reduced, thereby making the positrons The intensity of annihilation at the micro-defects is relatively reduced, so it is reduced. The Tc and magnetic inversion defects that affect the giant magnetoresistive material SrFMoq are also an important factor in the positron lifetime spectrum. As thought, the proportion of inversion defects in this experiment has a great relationship with the amount of doping. The change of inversion defects under illumination can also provide a certain explanation for the experimental results. Light irradiation causes atoms (such as F, eM) to be activated to vibrate violently. When Dangdang is> 20msn, lattice vibration starts to tend to SrFMO standard structure, so the proportion of anti-position defects decreases, so T decreases. There have been many reports on the research of inversion defects. Blao and Feng believe that the proportion of inversion defects in Sr (FexCr) M6 decreases monotonically with x, but decreases with Sr. When 0 05CXQ45 increases with it, Increase; Zhngm believes that the proportion of anti-site defects in (SfNa) 2FM6 compound is at x. It can be seen that long-life and short-life have the same change trend with the change of doping amount, and there are enough Size defects capture positrons. Due to the increase in light time, strong lattice vibration recombines large size defects into relatively larger size defects, so the long life T increases. Since the recombination of large size defects reduces the concentration of large size defects in the sample, 2 decreases. As the amount of light doping increases, the size of a large number of large-size defects that have become relatively large decreases relatively, which results in a sharp decrease in T. A large number of relatively large size defects make the intensity of positron annihilation at large size defects increase, so 2 increases. And the change of I can also be obtained by equation 1 + 1 = 1. The change of long life with the amount of doping can also be explained by the formation and change of electron coupler. When illuminated, due to the effect of light excitation, there is a competing process for the interaction between the positrons in the system and the irradiated electrons: the formation of shallow trapping or free scattering interactions. In a disordered environment, the formation of the PSS region is localized. With the increase of light time, the free volume excited to form ps decreases with the increase of temperature, and the positive and negative electrons form the annihilated localization. As the area becomes smaller, the number of localized electrons that form electron couplers decreases, so the long-life T increases. As the light progresses (when> 20mn), the electrons that form shallow traps are excited, and the Bloch electron concentration increases As the number of electron couples formed increases, the long life T decreases.
The change trend of T and T determines the change trend. On the whole, the average life is obviously reduced at 20mn, indicating that the continuous light doping makes the average size of the sample defect relatively reduce, which may be from micro-cavity, multi-cavity to double The hole or single hole transition makes the electronic structure tend to be ordered. Light excitation causes a large number of electron-hole pairs to be formed, so the average electron concentration increases with increasing doping amount. It can be seen from the above analysis that the positron lifetime parameter is very sensitive to the amount of light doping. The light doping method is a method that can change the carrier concentration of the material without complicatedly changing the chemical composition and crystal structure of the material, and has a unique role in studying the internal structure and defect characteristics of the substance.
3 Conclusion The traditional high-temperature solid-phase sintering reaction method was successfully used to prepare the double perovskite-type compound Sr.9G.1FMG6.
The results show that the positron lifetime parameter is very sensitive to the amount of light doping, and T and T have the same change trend with the light time; when the light time is> 20mn, the average electron concentration changes significantly with the light time; continuous light doping The average size of the sample defects is relatively reduced, which may be changed from micro-holes, multi-holes to double holes or single holes, so that the electronic structure tends to be ordered.
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