Magnetic Properties and Structure of (Cr_xAl_1‐x)₂O₃ Solid Solutions

Abstract

Statistical homogenity of (Cr,AI, -J20, solid solutions is investigated. It is shown, that there may be distinguished the region of statistical regularities and regions where prevail the clusters of two, three, and four chromic ions (111). The formation mechanism of solid solutions mentioned is proposed.Es wird die statistische HomogenitHt von (Cr,AI, -x)20,-Mischkristallen untersucht. Es wird gezeigt, daB unterschieden werden muB zwischen dem Bereich der statistischen Regularitaten und Bereichen, wo Cluster von zwei, drei oder vier Chromionen (111) vorherrschen. Der Bildungsmechanismus der erwahnten Mischkristalle wird vorgeschlagen.

Magnetic properties and structure of (FexAl1–x)2O3 solid solutions

“…The analogous situation has been observed in the case of (Cr,Al, -J203 solid solutions [4], the chromium distribution in the latter being close to statistical in the 0.01 5 x 5 0.1 concentration region. However, the x = f ( x ) dependences for (FexA1, -J203 essentially differ from those for (CrxAll-x)203 solid solutions.…”

“…The C2 = f(x) dependence passes through a maximum, and the relative concentration of the triplets (C,) increases with.growing x and exceeds the statistically computed one by more than 30 times. It must be noted that in the case of (Cr,Al, -J203 solid solutions the statistical distribution of Cr3+ ions has been observed in the 0.01 5 x 5 0.1 concentration range [4].…”

“…In [2] it has been considered that in case of small concentrations (x 5 0.15) it is necessary to take into consideration only groups of two and three Fe3+ ions as the probability of the formation of more-compound groups is rather small. An essential contribution of the four Cr3+ cation clusters to the (Cr,Al, -J203 magnetic susceptibility has been found [4] only at x > 0.4. More-compound independent clusters in (Me,Al, -x)20, solid solutions do not form apparently as far as four cations determine the structural element of corundum-like oxide, and groups with the greater number of cations than four may be always represented as a combination of the first three mentioned kinds of clusters.…”

“…with J , = 35 K. If we consider that in this concentration region three Fe3 + ion groups do not appear, or their number is negligibly small, the calculated J, value may be considered as the energy of exchange interaction in pairs. Table 1 represents the values of the cluster concentrations C i statistically calculated and experimentally found using (4). The statistical calculations have been made according to [8].…”

“…The susceptibility of the triplets has been reduced to the susceptibility of single ions and the probability of cluster formation with ferromagnetic exchange in oxide systems has been out of question. We have previously investigated the distribution of Cr3' ions in the (Cr,Al, -x)203 lattice [4]. The considerable contributions of groups of two, three, and four Cr3 + cations to the solid solution susceptibility has been noted.…”