Photoinduced Magnetic Effects in Magnetic Rare Earth Oxides

在77 K下，用激光（最有效波长为700 nm）或白色光辐照钇铁石榴石单晶，发现在室温以下140 K和210 K附近诱导出DA双峰，并伴随着低温下对退磁不敏感的磁导率不可逆下降的开始。这些晶体生长的一个修改的浮区法。这些是非常纯的，除了有意掺杂剂（Ga 0.0625摩尔或Ca 0.001摩尔）之外，既不掺入Si也不掺入Ca。在所有的样品中，相当大的氧空位被纳入的顺序为0.1摩尔%。在250K以下可以观察到这些现象，而将样品加热到室温可以恢复到原始状态。复磁导率μ '和μ”的温度依赖性的可逆和不可逆分量显示热滞后。在几个样品中，在室温附近观察到与辐照无关的额外DA峰。这些结果的背景下解释的配置坐标（CC）图与大晶格弛豫。我们对这两个过程的解释的基本概念如下。在黑暗中冷却，氧空位或深施主捕获双电子，形成所谓的F中心。当被俘获的电子从深能级被光激发到浅能级或导带时，畴壁的钉扎中心以可忽略不计的小俘获率产生。DA的起源将被认为是与主要重点的氧空位的电荷依赖性的流动性。

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.