Epitaxial growth and magnetic behavior of NiFe₂O₄ thin films

Abstract

Thin films of NiFe2O4 were deposited on SrTiO3 (001) and Y0.15Zr0.85O2 (yttria-stabilized zirconia) (001) and (011) substrates by 90°-off-axis sputtering. Ion channeling, x-ray diffraction, and transmission electron microscopy studies reveal that films grown at 600 °C consist of ∼300 Å diameter grains separated by thin regions of highly defective or amorphous material. The development of this microstructure is attributed to the presence of rotated or displaced crystallographic domains and is comparable to that observed in other materials grown on mismatched substrates (e.g., GaAs/Si or Ba2YCu3O7/MgO). Postdeposition annealing at 1000 °C yields films that are essentially single crystal. The magnetic properties of the films are strongly affected by the structural changes; unannealed films are not magnetically saturated even in an applied field of 55 kOe, while the annealed films have properties comparable to those of bulk, single crystal NiFe2O4. Homoepitaxial films grown at 400 °C also are essentially single crystal.

Strain-induced stabilization of new magnetic spinel structures in epitaxial oxide heterostructures

“…As an explanation for the higher M s observed in the thinner films, we consider the possibility for the structure to experience a transition to the normal spinel structure, where trivalent ions are only found in [B] [8] and Lüders et al [7] invoked the same argument to account for the observation of an enhanced magnetization of ultrathin NFO films. It is worth however to mention that, so far, no other evidence has been reported.…”

“…Interestingly enough, however, the saturation magnetization of ultrathin films of NiFe 2 O 4 has been found to be substantially larger than bulk magnetization [7]. This unexpected result has been attributed to the out-of-equilibrium atomic distribution resulting from growth conditions [7,8] although definite explanation remains to be settled.…”

Growth and characterization of superconducting spinel oxide thin films

“…Previous studies on films with antiphase boundaries have shown that high-temperature annealing results in grain growth and a reduction in antiphase boundary density. 56 A further crossover as a function of thickness from a logarithmic dependence to exponential temperature dependence of sheet resistance and stronger localization occurs for the thinnest films (e.g. Figure 7 (a) or (b) t =14.6 nm), and this normal-state resistance crossover is accompanied by a subsequent complete suppression of the superconducting transition.…”

Study of magnetization and crystallization in sputter deposited LiZn ferrite thin films

“…A large number of articles have recently reported various types of ferrite films prepared using different techniques. [1][2][3][4][5][6][7] Though the bulk properties of ferrites are fairly well understood, it is found that it has only rarely been possible to achieve all these properties when deposited in thin film form. Moreover, certain new phenomena have been noted in the case of thin films that are not clearly understood.…”

“…11 Another phenomenon that has been specific to ferrite thin films, has been the observation of a large high field susceptibility. 5,6 There have not been many systematic studies carried out in sputter deposited ferrite thin films to investigate the evolution of saturation magnetization and other magnetic properties, and to understand the reasons of their difference from bulk materials. We have recently reported some studies on the rf sputter deposited LiZn ferrite films of composition Li0 0.5Ϫx/2 Mn 0.1 Zn x Fe 2.35Ϫx/2 O 4 with xϭ0, 0.16, 0.32, and 0.48.…”