Ferrimagnetic ZnFe₂O₄ thin films on SrTiO₃ single crystals with highly tunable electrical conductivity

Abstract

Within the current search for spintronic materials with spin polarized electronic conductivity, the spinel-type ferrite materials gain more and more interest due to their comparably high intrinsic magnetic moments that are based on strong antiferromagnetic superexchange interaction between A and B ions. In case of normal spinels as for example ZnFe 2 O 4 (ZFO), additional disorder on the tetrahedral (A-Zn 2+) and octahedral ) lattice sites leads to effective ferrimagnetism.Suzuki [1,2] further pointed out that ferrite thin films show strong magnetic coupling, high resistivity, and lowloss characteristics at high frequencies, making them suitable for flux guides and sensors in thin film recording heads. ZFO thin films deposited on fused quartz show a grain size dependent spontaneous magnetization [3]. Thin Fe 3-x Zn x O 4 films with 0 ≤ x ≤ 0.9 show spin polarized carriers at 300 K, as confirmed by photoemission spectroscopy [4]. Semitransparent and conducting ZFO films with Curie temperature above 600 K were demonstrated on MgAl 2 O 4 substrates [5]. A photomagnetic effect up to 8.1% due to HeNe illumination was observed in (MnZnFe) 3 O 4 films [6]. These properties indicate the potential of Zn-ferrite films for room-temperature spintronic applications [7,8].In this Letter, we present the high tuneability of conductivity of ZFO thin films on SrTiO 3 (STO) substrates.

Magnetite nanoparticles prepared by co-precipitation method in different conditions

“…An interesting coincidence is that the highest ZFA was also observed in doped ferrite having flattened grains. Another interesting example is given by Lorenz et al [37] where they had shown the possibility to control conductivity at 300 K with pulsed laser deposition conditions for ZnFe 2 O 4 spinels. The differences in microwave behaviour of MÀI and MÀII MNPs can be used in the design of multilayered microwave radiation absorbing structures having different nanoparticles as fillers of different layers.…”

Structure and cation distribution of (Mn0.5Zn0.5)Fe2O4 thin films on SrTiO3(001)

“…Angular dependent measurements of the reflections of SrTiO 3 (311) and (Mn,Zn)Fe 2 O 4 (511) were carried out showing only parallel orientations of the layer to the substrate, which is similar to the behavior of ZnFe 2 O 4 on SrTiO 3 . 17,23,24 It can be speculated that this epitaxial growth is possible due to a large dislocation density at the interface that subsides throughout the film and causes a gradual change of the lattice constant within a few layers.…”

“…11 Because of the lattice mismatch and the possible diffusion of titanium into the layer, the magnetic properties of the layer are reported to differ from the bulk properties. 6,9,[15][16][17][18][19] Nevertheless, it was still possible to grow layers directly on SrTiO 3 without such buffer layers although the layers exhibited lattice parameters pointing to a large strain, which might be the reason of the variations in the films. Additionally, ferrites grown without buffer layers have shown magnetic properties, which makes them interesting candidates for various applications.…”

“…Additionally, ferrites grown without buffer layers have shown magnetic properties, which makes them interesting candidates for various applications. [2][3][4]6,9,[15][16][17][18] One of the notably interesting ferrites for such layer systems is the mixed manganese zinc ferrite (Mn 1Àx 4 ) is up to 9% depending on the composition of manganese zinc ferrite. Nevertheless, a complete growth study using different growth conditions regarding substrate temperature (500 to 1000 K), oxygen partial pressure (6 Â 10 À5 to 0.1 mbar), and post-growth annealing has been carried out, while here the results of the optimized growth process are presented.…”

“…As reported for ZnFe 2 O 4 before, the preparation of the layer yielding the best composition as determined by x-ray photoelectron spectroscopy (XPS) as well as very sharp reflections in x-ray diffraction (XRD) has been chosen to be presented. 17,23 With the optimized growth conditions, it was possible to grow a crystalline, epitaxial layer as shown here.…”