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81.
N. Volkov G. Petrakovskii P. Böni E. Clementyev K. Patrin K. Sablina D. Velikanov A. Vasiliev 《Journal of magnetism and magnetic materials》2007
The study of magnetic and magnetotransport properties of the crystals of (La1−yEuy)0.7Pb0.3MnO3 system has been carried out. Eu ions enter the crystals being in trivalent nonmagnetic state. Europium ions possessing of smaller ionic radius in comparison with La ions, induce local distortions of Mn–O–Mn bonds in the system that cause random distribution of magnetic exchange interactions in magnitude and, probably, in sign. The competition of magnetic interactions leads to the appearance of the inhomogeneous magnetic state in the crystals. The enhancement of concentration of Eu ions results in decrease of the Curie temperature and broadening of the inhomogeneous magnetic state area. At y=0–0.4 the coexistence of the paramagnetic phase with conductivity of the polaronic type and the ferromagnetic metallic phase is observed in a bounded temperature interval both above and below TC. Below TC the increasing of y up to 0.6 induces the magnetic state representing the coexistence of two different FM phases. These phases are spatially separated due to frustration of FM and AFM exchange interactions on phase boundaries. Above TC, up to 1.6TC ferromagnetic clusters exist in a paramagnetic matrix similar to the case of samples with y=0–0.4. Concerning electric properties, the samples with y=0–0.4 reveal the metal–insulator transition at temperature that practically coincides with TC. The sample with y=0.6 has conductivity of insulator character up to the lowest temperatures. For all investigated compositions y=0–0.6 the CMR effect is observed in the area where the inhomogeneous magnetic state exists. The effect is determined by different conductivity of the coexisting phases, as well as by sensitivity of the inhomogeneous state to external magnetic field. 相似文献
82.
N. B. Ivanova N. V. Kazak Yu. V. Knyazev D. A. Velikanov L. N. Bezmaternykh S. G. Ovchinnikov A. D. Vasiliev M. S. Platunov J. Bartolomé G. S. Patrin 《Journal of Experimental and Theoretical Physics》2011,113(6):1015-1024
Co3O2BO3 and Co2FeO2BO3 single crystals with a ludwigite structure are fabricated, and their crystal structure and magnetic properties are studied
in detail. Substituted ludwigite Co2FeO2BO3 undergoes two-stage magnetic ordering at the temperatures characteristic of Fe3O2BO3 (T
N1 ≈ 110 K, T
N2 ≈ 70 K) rather than Co3O2BO3 (T
N
= 42 K). This effect is explained in terms of preferred occupation of nonequivalent crystallographic positions by iron, which
was detected by X-ray diffraction. Both materials exhibit a pronounced uniaxial magnetic anisotropy. Crystallographic direction
b is an easy magnetization axis. Upon iron substitution, the cobalt ludwigite acquires a very high magnetic hardness. 相似文献
83.
G. A. Petrakovskii T. V. Drokina A. L. Shadrina D. A. Velikanov O. A. Bayukov M. S. Molokeev A. V. Kartashev G. N. Stepanov 《Physics of the Solid State》2011,53(9):1855-1858
The SmFeTi2O7 compound has been synthesized using the solid-phase reaction method. In order to determine the magnetic state, X-ray structural, Mössbauer, calorimetric, and magnetic measurements have been performed. The state of spin glass with the freezing point T f = 7 K has been found for SmFeTi2O7. 相似文献
84.
V. G. Myagkov V. S. Zhigalov A. A. Matsynin L. E. Bykova G. V. Bondarenko G. N. Bondarenko G. S. Patrin D. A. Velikanov 《JETP Letters》2012,96(1):40-43
Results of an X-ray diffraction study as well as magnetic and electrical measurements of the solid-state reactions in Ge/Mn polycrystalline films of an 80/20 atomic composition have been presented. It has been shown that the ferromagnetic Mn5Ge3 phase is formed first on the Ge/Mn interface after annealing at ??120°C. The further increase in the annealing temperature to 300°C leads to the beginning of the synthesis of the Mn11Ge8 phase, which becomes dominating at 400°C. The existence of new structural transitions in the Mn-Ge system in the region of ??120 and ??300°C has been predicted on the basis of the presented results and results obtained earlier when studying solid-state reactions in different film structures. The supposition about the general chemical mechanisms of the synthesis of the Mn5Ge3 and Mn11Ge8 phases during the solid-state reactions in the Ge/Mn films of the 80/20 atomic composition and the phase separation in Ge x Mn1 ? x (x > 0.95) diluted semiconductors has been substantiated. 相似文献