Point Defects in Electron‐Irradiated Stoichiometric Magnetite

Abstract

High‐purity, stoichiometric, single crystalline magnetite (Fe3O4) has been electron (e−)‐irradiated below 45 K to a dose of 1023 electrons/m2. Radiation‐induced point defects give rise to both drastic modifications of intrinsic electronic processes and the occurrence of reorientation‐type magnetic relaxations. Both phenomena offer deeper insights into the mechanisms of (i) electronic charge transport and (ii) thermally activated reactions of interstitials and vacancies. Coordination between migration of elementary defects and corresponding anncaling stages can be established in Fe3O4 with higher precision than in any other magnetic system investigated so far.

Analysis of Magnetic After-Effects in Gallium Ferrites

“…Fig. 1a, b [4,13]. On the other hand, fitting was still possible in this crystal for the respective hopping plateau, despite its typically defect-induced modifications [4 to 11], i.e.…”

“…Thus, it has been suggested that e.g. in the above-mentioned compounds, due to alternatively induced stresses intrinsic interstitials, too, may have formed giving rise, similarly as in e À -irradiated magnetite, to the reorientationtype process IV near 200 K [6,11,13].…”

“…As described in detail previously [6,9,13], each individual peak of a composed MAE spectrum (Section 2.2) is approximated by a continuous, box-type distribution of simple Debye processes with respective relaxation times t i t 0i e Q i akT . Accordingly, such peaks are characterized by a central activation enthalpy Q i , the width of their respective enthalpy distribution Q i À DQ i a2 Q Q i DQ i a2, and a pre-exponential factor t 0i , cf.…”

“…In perfect magnetite, valency fluctuations of the type being inherently accompanied by local anisotropy transport between zero-momentum Fe 3 and residual momentum Fe 2 ions, are the sources of pronounced magnetic lowtemperature relaxation processes. As a well-known fact, the corresponding mechanisms of low-temperature electron-exchange via tunnelling (4 K`T`35 K and hopping (50 K`T`125 K are severely affected already by faintest deviations from the perfect structural or electronic crystal order as induced, i.e., by a) octahedral (B-site) lattice vacancies, in concentrations down to D 10 À6 [2 to 4], b) ionic substitutions, starting at levels of x 10 À4 [4 to 12] or c) intrinsic point defects (vacancies and interstitials) as, e.g., produced during low-temperature electron irradiation [13]. Similarly, the Verwey transition %125 K, too, is strongly impinged ± ± concerning reaction-order and temperature position ± ± by any deviation from the perfect, stoichiometric crystal structure [1 to 13].…”

Irradiation-Induced Electron Tunnelling and Small-Polaron Hopping in Single-Crystalline YIG

“…One of the most fascinating features of this study was the observation of an intermediate transformation of the initial radiation-damaged low-temperature (T < 60 K) spectrum, after annealing to a temperature of T a ¼ 523 K, into a structure resembling that of the wellknown low-temperature spectrum of undisturbed, stoichiometric magnetite (Fe 3 O 4 ), [2][3][4][5], cf. Figs.…”