Expeditions of the institute of geography RAS during the 20th–21st centuries (to the 100th anniversary of the institute)

In the lead-up to the 100th anniversary of the Institute of Geography RAS, we summarized the salient features and chronology of its field investigations into the country’s nature and resources during the 20th-21st centuries. It is shown that the institute’s history has embodied all stages of evolution of national geography: the traditions of the late 19th century with their departure from the perception of geography as a “descriptive” science and the development of genetic (V.V. Dokuchaev’s) and chorological (A. Hettner’s) approaches, the development of the sectoral specialization of science, the introduction of modern methods: remote sensing, navigation and geoinformation technologies, and the formation of the geography of the 21st century as a philosophical phenomenon and a synthetic discipline with profound prospects for a better understanding a rapidly changing worl

Magnetic properties of manganites doped with gallium, iron, and chromium ions

The magnetization and the crystal structure of the La0.7Sr0.3Mn1 amp; 8722; x M x O3 M Ga, Fe, Cr; x amp; 8804; 0.3 systems are studied. The substitution of gallium and chromium is shown to cause phase separation into antiferromagnetic and ferromagnetic phases, whereas the substitution of iron for manganese stabilizes a spinglass state. The ferromagnetic phase in the chromium substituted compositions is much more stable than that in the case of substitution by iron ions or diamagnetic gallium ions. The magnetic properties are explained in terms of the model of superexchange interactions and the localization of most e g electrons of manganese. The stabilization of ferromagnetism in the chromium substituted compositions can be caused by the fact that the positive and negative contributions to the superexchange interaction between Mn3 and Cr3 ions are close to each other but the antiferromagnetic part of the exchange is predominant. Moreover, some chromium ions are in the tetravalent state, which maintains the optimum doping condition