Photoinduced Magnetic Effects in Magnetic Rare Earth Oxides

在激光（最有效波长为700 nm）和白光（77K）照射下，钇铁石榴石单晶在室温下140K和210K左右会出现DA双峰，且磁导率在低温下不可逆下降，对退磁不敏感。这些晶体是通过改进的浮区法生长的。这是非常纯的，除了有意掺杂（Ga 0.0625 mol或Ca 0.001 mol）外，既没有Si也没有Ca。在所有样品中都含有相当大的氧空位，约为0.1 mol %。这些现象在250K以下可以观察到，而将样品加热到室温可以恢复到原来的状态。可逆组分和不可逆组分的温度依赖性复渗透率mu'和mu"表现出热滞后。在一些样品中，在室温附近观察到一个与辐照无关的附加DA峰。这些结果在具有大晶格弛豫的构型坐标（CC）图的背景下解释。;我们解释这两个过程的基本概念如下。在黑暗中冷却，氧空位或深层供体捕获双电子，形成所谓的f中心。当捕获的电子从深能级被光激发到浅能级或导带时，畴壁的钉住中心以可忽略不计的小捕获率产生。DA的起源将被考虑，主要强调氧空位的电荷依赖迁移率。

In single crystals of yttrium iron garnet irradiated with laser (the most effective wavelength is 700 nm) or white light at 77K,double peaks of DA around 140K and 210K below room temperature were found to be induced with correlative onset of the irreversible decrease of permeability insensitive to demagnetization at low temperature. These crystals were grown by a modified floating zone method. These is very pure, with neither Si nor Ca incorporated except for intentional dopants (Ga 0.0625 mol or Ca 0.001 mol). In all samples a considerable oxygen vacancy is incorporated of the order of 0.1 mol %. These phenomena are observable below 250K,while the original state may be restored by warming the sample to room temperature. Reversible and irreversible components of the temperature dependence of complex permeabilities mu' and mu" shows a thermal hysteresis. In several samples, an additional DA peak independent of irradiation is observed around room temperature. These results are interpreted within the context of configuration coordinate (CC) diagrams with large lattice relaxations. ; the basic concept of our explanation of both processes is as follows. Cooled in the dark, oxygen vacancies or deep donors capture the double electrons and so called F-centers are formed. Pinninng centers for domain walls is created with negligibly small capture rates, when the trapped electrons are photoexcited from the deep levels to the shallow levels or conduction band. An origin of DA will be considered with the main emphasis on a charge dependent mobility of oxygen vacancies.