Europium Monoxide by Arnold S. Borukhovich & Alexey V. Troshin

Author:Arnold S. Borukhovich & Alexey V. Troshin
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

It is seen that under these conditions the T c2 quantity of a quasi-degenerate sample (b) increases by 3°. The pressure practically does not affect the magnetization of the sample. The value of the pressure coefficient is ∂T c /∂P = (3.8 ± 0.2) × 107 K/Pa.

A different effect is exerted by the pressure applied to the parameters of a sample of a non-degenerate solid solution of the Eu0.92Sm0.08O (a). The initial increase in the applied pressure within the limits 0 < P < 6.2 × 108 Pa leads only to an increase in the magnetization of the sample (by 20%) with its constant T c2 = 124 K. The further increase in the pressure applied to the sample, affecting the magnitude of its magnetization to a lesser extent, leads to an increase in the Curie temperature, so that for P = 8 × 108 Pa ΔT c2 ≈ 3 K. This unusual, in two stages, action of high pressure on the magnetic parameters of samples of magnetic semiconductors with non-degenerate type of semiconductor conductivity was observed for the first time. Nevertheless, this behavior of the magnetization does not contradict the theory of magnetic quasimolecules and, most likely, is a reflection of their contribution to the characteristics under discussion. In fact, since for magnetic quasimolecules their magnetic susceptibility is χ ~ M 2 [7], then an increase of the sample magnetization upon applying pressure to it can mean an increase in the “effective” volume of the quasimolecule. That is, the inclusion of europium cations from the next nearest second coordination sphere, N > Z 1 = 12, in its composition. This entails delocalization and increase in the radius of the electron orbit of samarium 5d 1-electron. Implementation of such a process can lead to the fusion of neighboring magnetic quasimolecules with the formation of complexes of conducting regions with an increased electron concentration. Due to such a nature of ferromagnetic interactions, the increasing in them will cause an increase of T c of such a solid solution, which is apparently observed in the experiment in Fig. 3.13a at P > 6.2 × 108 Pa. Estimates made on the basis of the presented experimental data show that the reduction in the crystal lattice period of the sample at pressures reached in [22] is Δa = 0.001 nm. Such a change of Δa, as already indicated, is characteristic when the semiconductor conductivity of EuO crystals degenerates under conditions of their all-round compression. Thus, the data presented make it possible to follow up the peculiarities of the manifestations of the exchange interaction both inside and between magnetic quasimolecules in a ferromagnetic semiconductor of the Eu0.92Sm0.08O composition under high-pressure conditions.

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