Ferromagnetic resonance (FMR) in the dependence on magnetic field orientation, and effect of the laser light on the magnetic ordering were studied in colossal magnetoresistance films, La1−xSrxMnO3 and La1−xBaxMnO3. The FMR linewidth increased with the decrease in temperature in La1−xSrxMnO3 films, and was nearly temperature independent in La1−xBaxMnO3, that was attributed to the different degree of magnetic homogeneity of the films. Layered structures La1−xBaxMnO3 on silicon with intermediate layer of SrTiO3 were characterized by FMR as highly homogeneous. From the orientation and temperature dependences of the FMR spectra, the effective magnetization, and effective anisotropy fields were estimated. The laser light illumination resulted in the change of FMR line shape and intensity, and was interpreted in terms of optically induced magnetic disordering and effective heating of the spin system.
We report on the ferromagnetic resonance studies on ZnMnO films grown by the pulsed-laser deposition technique. ZnMnO films were annealed in different atmospheres. The films grown and annealed in oxygen demonstrate ferromagnetic behavior at room temperature and below. However, annealing in either nitrogen or argon deteriorates the ferromagnetic response of the films. Further annealing the films in oxygen recovers the ferromagnetic response. Our results suggest that oxygen plays a major role for controlling the ferromagnetic properties in ZnMnO films.
We report that the dielectric constant can be increased in amorphous thin film TaxGe1−xOy over pure amorphous Ta2O5. With only 3% substitution of Ge for Ta the relative dielectric constant εr rises to 30.5, a 40% increase over the value obtained for pure amorphous Ta2O5 films deposited under identical conditions (εr=22). No enhancement is observed in the optical dielectric constant (i.e., refractive index). This suggests that the enhancement is dominated by the effects in the ionic polarizability rather than the electronic polarizability. This system represents a valuable opportunity to explore the sensitive relationship between bonding and electronic properties in amophous oxides.
We describe the deposition of insulating tantalum oxide thin films under conditions of controlled ion bombardment, which can be achieved using reactive sputtering on 90° off-axis substrates with an applied substrate bias. Capacitive measurements of Ta2O5 deposited on unbiased off-axis substrates indicate low frequency dielectric constants as high as εr∼300. Low frequency loss tangents are high, tan δ>0.5, and have a pronounced frequency dependence. Deposition of the film off-axis with sufficient applied rf bias to the substrate (negative bias >−70 V) recovers the on-axis properties typical of Ta2O5, e.g., εr∼22 and tan δ∼0.02. The recovery of normal dielectric behavior is attributed to the ion bombardment of the growing film under substrate bias, similar to on-axis depositions but absent from depositions on off-axis substrates with no applied substrate bias. We suggest that insufficiently bombarded films develop a Maxwell–Wagner type polarization along columnar voids. The void structure and the associated dielectric response vary with distance from the sputtering source due to variations in ion density and angle from the sputtering source. A similar dielectric response is observed in depositions on on-axis substrates as a function of angle from the central sputter gun axis. Our results suggest that ion bombardment is necessary for good quality sputtered dielectric films but that a controlled Ar+ flux is essentially equivalent to the uncontrolled O2−/O2− flux of on-axis reactive sputtering.
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