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.

The dielectric function of ZnFe2O4 thin films has been studied in a wide spectral range from 0.5 eV to 9 eV. The observed optical transitions are identified as charge transfer and ligand field transitions. We propose a parametric model based on known model dielectric functions that fits well to the experimental data. The assignment of optical transitions is justified by a thorough comparison with optical data from other materials exhibiting similar transitions. The main contributions to the optical response are found to arise from charge transfer transitions from the O2p to the metal ion 4s and 3d bands. Furthermore weak crystal field transitions are observed. The evolution of the dielectric function as well as the crystal quality of the thin films with respect to growth temperature is further analyzed. A blue shift of the observed optical transitions is related to a relaxation of the lattice toward the bulk and an increase of the crystal quality with increasing growth temperature.

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Due to the large demand for optoelectronic devices covering the spectral range from green to ultraviolet, extensive research has been triggered into wide-bandgap group III-nitride semiconductors. Since InGaN-based devices exhibit a strong decrease in efficiency advancing the green spectral region [1], ZnO-based devices are a promising alternative.An emission energy in the visible spectral range was obtained in e.g. Zn 1-x Cd x O/ZnO quantum wells (QWs) or double heterostructures [2,3]. Large Cd contents up to ≈0.50 with emission energies down to 1.8 eV were obtained in wurtzite Zn 1-x Cd x O thin films [4], making a wide spectral range accessible. However, up to now only few publications exist that report on Zn 1-x Cd x O/ZnO QWs exhibiting emission energies far below theZnO bandgap resulting from difficulties to obtain large Cd contents in the QWs due to the low solubility of Cd in ZnO.For PLD-grown samples the lowest reported QW emission energy is as high as 2.76 eV. QW energies down to 2.2 eV are accessible for molecular beem epitaxy-grown samples, supported by the occurrence of the Quantum Confined Stark Effect (QCSE) [1], that is expected to occur in samples with a polar growth direction. Sadofev et al. [2] have up to now exclusively proved the occurrence of the QCSE, by obtaining emission significantly below the respective thin film emission energies. Matsui et al. concluded the occurrence of the QCSE as they obtain excitation-power dependent QW energies and a decrease of the degree of localization and the thermal activation energy of the PL-intensity quenching with increasing QW thickness [5]. However, they were not able to tune the emission energy significantly below that of the thin film. The absence of the QCSE in the other studies can be understood following the argumentation of Brandt et al. [6], who explained it for PLD-grown ZnO/Mg x Zn 1-x O QWs with reduced interface abruptness.In this Letter, optical properties of Zn 0.75 Cd 0.25 O/ZnO MQWs with small QW thicknesses are studied. They were deposited at low temperatures in order to achieve a high Cd content. MQWs were deposited to enhance the luminescence intensity and precisely determine the QW thickness by using X-ray diffraction (XRD). Due to the high Cd content, the MQW emission energy was tuned from 2.5 eV to 3.1 eV by varying the QW thickness.The MQW structures were grown on a-plane sapphire substrates using PLD. Sintered ceramic targets of highly Polar c-axis oriented Zn 0.75 Cd 0.25 O/ZnO multiple quantum wells (MQWs), grown by pulsed-laser deposition (PLD), emitting in the visible spectral range are reported. By applying a low growth temperature of ≈ 300 °C a large Cd content of 0.25 and abrupt interfaces could be achieved using PLD. The emission energy was tuned from the green to the violet spectral range (2.5 eV to 3.1 eV) by tuning the quantum well thickness. It is determined by the quantum confinement effect and the quantum-confined Stark effect.Intensity (arb. units) 2.0 2.5 3.0 Energy (eV) increasing well width

Multiferroic composite thin films prepared from ferrimagnetic zinc ferrite (ZFO) and ferroelectric barium titanate (BTO) show sizable magnetic exchange bias. After field cooling in +3 T, an exchangebias field of about 237 mT for a 65% ZFO/35% BTO and of about 234 mT for a 35% ZFO/65% BTO composite is observed at 10 K. Exchange biasing is accompanied by a significant vertical loop shift of about 10% of the total saturation magnetization after field cooling in 3 T. The composite films show simultaneous ferromagnetic, ferroelectric and magnetocapacitance effects. Depending on the ZFO to BTO ratio of the target for pulsed laser deposition, the composite films show either preferential spinel-or perovskite-like X-ray diffraction patterns. Raman spectra of the composites are dominated by broadened peaks at positions near the phase-pure BTO or doped ZFO. The composite films show nm-size amorphous precipitates in a ZFO-like matrix, which are most probably responsible for the observed exchange bias effects.