Charge Transport Mechanisms in Single Crystalline Yttrium Iron Garnet as Resolved by Magnetic Relaxations

Abstract

Single crystalline Yttrium Iron Garnet (YIG) has been irradiated at T % 80 K with 3 MeV electrons to a dose of ! 10 19 e À cm À2 and the recovery of the induced lattice damages, after systematic annealing over the temperature range 80 K < T a < 1400 K, is carefully investigated by means of magnetic after-effect (MAE) spectroscopy, covering the range 4 K < T < 500 K. The wide extension of recovery is attributed, besides to Fe 3 and Fe 2 interstitials and their associated d-and a-site vacancies, especially to the larger, and hence less mobile, Y 3 interstitialcies and their c-type vacant sites. The obtained data allow to resolve various charge transport mechanisms: (i) tunneling of electrons in combination with intra-atomic excitations in the low-temperature zone (4 K < T < 55 K); (ii) small-polaron hopping, extended over the range 80 K < T < 350 K; (iii) primarily radiation-induced, Debye-type ionic reorientation processes with peak temperatures near to 250, 325 and 400 K.Einkristalliner Yttrium-Eisen-Granat wurde bei T % 80 K mit 3 MeV-Elektronen auf eine Dosis von ! 10 19 e À cm À2 bestrahlt und die anschlieûende Erholung der Gitterfehler, nach systematischem Anlassen u È ber einen Temperaturbereich von 80 K < T a < 1400 K, mit Hilfe magnetischer Nachwirkungsspektroskopie im Gebiet 4 K < T < 500 K sorgfa È ltig untersucht. Der weit ausgedehnte Erholungsbereich wird, neben Fe 3 und Fe 2 Zwischengitter-Ionen und deren zugeho È riger d-und a-Platz Leerstellen, hauptsa È chlich den gro È ûeren, und damit unbeweglicheren, Y 3 ZwischengitterIonen und ihren c-Platz Leerstellen zugeordnet. Die gewonnenen Daten erlauben eine deutliche Unterscheidung folgender Ladungstransport-Vorga È nge: (i) Tunneln von Elektronen in Verbindung mit intra-atomarer Anregung (4 K < T < 55 K); (ii) Klein-Polaron-Hu È pfen im Bereich 80 K < T < 350 K; (iii) bestrahlungsinduzierte, durch Ionenspru È nge verursachte Debye-Prozesse mit Maximumtemperaturen von 250, 325 und 400 K.

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

“…The isotherms of the ensuing higher temperature relaxations, too, are of logarithmic time dependence, both in YIG (cf. [1]) and Fe 3 O 4 (cf. Fig.…”

“…As described in more detail in [1,6], the YIG single crystals were grown from the melt, using a PbO-PbF 2 Á B 2 O 3 flux. X-ray diffraction in combination with inductively coupled plasma spectroscopy yielded a flux-induced impurity content of 0.05 mol% Pb; in addition, a certain oxygen deficiency has been deduced from preceding MAE investigations [1,6].…”

“…X-ray diffraction in combination with inductively coupled plasma spectroscopy yielded a flux-induced impurity content of 0.05 mol% Pb; in addition, a certain oxygen deficiency has been deduced from preceding MAE investigations [1,6]. Of this material, prisms with dimensions 1:4 Â 1:4 Â 10 mm 3 were cut along the [111] crystal direction and e À -irradiated at 80 K to a dose of !10 23 e À m À2 , using the Dynamitron of the Institut fü r Strahlenphysik der Universitä t Stuttgart.…”

“…In a recent paper we have reported on various charge transport mechanisms, found to have been induced in single crystalline yttrium iron garnet (YIG) after low-temperature electron (e À )-irradiation in the course of subsequent, systematic annealing [1]. 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.…”

“…Typically, these two similar spectra are composed of a plateau-like relaxation zone, extending from lowest temperatures (T < 5 K) up to T < 45 K in YIG, or T < 25 K in Fe 3 O 4 , being followed by a pronounced Debye peak at 50 K (YIG) or 30 K (Fe 3 O 4 ), respectively. In [1] this low-temperature phenomenon in e À -irradiated YIG has been discussed rather shortly as only one among several other, most interesting variations, the YIG spectrum is undergoing upon annealing over the wide range of 80 K < T a < 1400 K (!). The striking similarity of the spectra in partly recovered YIG and Fe 3 O 4 has been associated with an inherent correspondence of the respective relaxation mechanisms in both systems.…”