Magnetic After‐Effects in Single‐ and Poly‐Crystalline Magnetite

Abstract

The magnetic relaxation spectra of different types of single crystalline magnetite are investigated in the temperature range 4 IC < 27 < 450 K and compared with corresponding spectra obtained on stoichiometric (Fe,O,) and vacancy-doped polycrystals (Fes-dO,). Three basic relaxation mechanisms are revealed within the following temperature ranges 4 K < TI < 35 K, 40 K < < T~I < 130 I< and 200K< !7'111< 450 lC, which may be associated t o either electronic ( T I , T I I ) or ionic ( TIII) hopping processes. I n crystals with systematically reduced stoichiometry characteristic modifications in the structure of these spectra are observed from which additional information for a theoretical understanding may be obtained.

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.…”

“…1a, b present the numerically determined enthalphy distributions of the electronic low-temperature relaxations, as observed in low-doped vacancy-absent Ga-ferrite x 0X05 and perfect, monocrystalline magnetite. For the ease of following the variation of the basic process III in dependence of the Ga concentration, the prototype of this peak ± ± as observed in high-purity, vacancy-doped polycrystalline magnetite [2,4] ± ± is shown in Fig. 2a.…”

“…These vacancies are prerequisite for the occurrence of the ionically induced reorientation processes III and II [4,11], whose reactions on various Ga contents were a main subject of our present investigations.…”

Investigation of the garnet–perovskite transition in Nd doped YIG by means of magnetic disaccommodation

“…The study of magnetic relaxations, which is technologically important to minimize losses, provides also information about the underlying mechanisms governing the dynamic behaviour of Bloch walls [1]. Measurement of magnetic disaccommodation is a sensitive way to study magnetic relaxations in ferrites.…”

“…It consists in the time variation of the mobility of domain walls after a magnetic shock, and is shown by a temporal evolution of the magnetic permeability after a demagnetization stage. The origin of this relaxation phenomenon, which has been observed both in cubic spinel ferrites [1], hexaferrites [2] and garnets [3], has been attributed to either the rearrangement or the diffusion of anisotropic point defects (lattice vacancies, interstitials) within the Bloch walls [1], and the relaxation time which characterizes each relaxation process is strongly temperature-dependent. Yttrium iron garnets (YIG) are excellent ferrimagnetic materials for use in microwave devices due to their good properties -high electrical resistivity and narrow resonance linewidth -at high frequencies together with the possibility of tailor their properties by introducing dopants [4].…”