Polarized Raman spectra of NiFe 2 O 4 (NFO) films of varying thickness and growth temperature are investigated and discussed. We find that the relaxed films obtained at higher temperatures on MgAl 2 O 4 (MAO) substrate exhibit spectra identical to those of single crystals and provide strong indications for ordering of Ni 2+ and Fe 3+ at the octahedral sites. There is evidence for a certain degree of B-site ordering even for the thinnest film and the ones grown at the lowest temperature. The variations of Raman mode frequencies and lattice parameters with growth temperature and film thickness provide evidence that the volume of the unit cell decreases under the compressive strain of the NFO film-MAO substrate mismatch. In general, we conclude that the film relaxation and the B-site ordering are more sensitive to the growth temperature rather than to the film thickness. Even relatively thin films grown at high temperatures show almost-relaxed lattice parameters and enhanced B-site ordering unlike the low-temperature films, which remain strained even when they are thick.

We have studied the magnetic anisotropy of nanometric CoFe 2 O 4 ͑CFO͒ thin films grown on ͑100͒SrTiO 3 ͑STO͒ substrates. It has been found that epitaxial substrate-induced compressive strain makes the normal-to-film axis harder than the in-plane directions. In agreement with some previous reports, the magnetization loops are found to display a characteristic shrinking at low fields. Detailed structural and microstructural analyses, together with a modeling of the magnetization loops, revealed that the microstructure of the films, namely, the coexistence of a continuous CFO and a distribution of pyramidal CFO huts emerging from the surface, are responsible for this peculiar feature. We argue that this behavior, which significantly impacts the magnetic properties, could be a general trend of spinel films grow on ͑001͒STO substrates.

We have performed point-contact spectroscopy measurements on a sample constituted by a metallic ferromagnetic oxide ͑SrRuO 3 ͒ bottom electrode and a tunnel ferrimagnetic ͑CoFe 2 O 4 ͒ barrier. Andreev reflection is observed across the tunnel barrier. From the comparison of Andreev reflection in SrRuO 3 and across the CoFe 2 O 4 barrier we infer that the ferrimagnetic barrier has a spin filter efficiency not larger than +13%. The observation of a moderate and positive spin filtering is discussed in the context of the microstructure of the barriers and symmetry-related spin-filtering effects.

We report here on the growth of NiFe 2 O 4 epitaxial thin films of different thickness (3 nm ≤ t ≤ 32 nm) on single crystalline substrates having spinel (MgAl 2 O 4 ) or perovskite (SrTiO 3 ) structure. Ultrathin films, grown on any of those substrates, display a huge enhancement of the saturation magnetization: we will show that partial cationic inversion may account for this enhancement, although we will argue that suppression of antiparallel collinear spin alignment due to size-effects cannot be excluded. Besides, for thicker films, the magnetization of films on MAO is found to be similar to that of bulk ferrite; in contrast, the magnetization of films on STO is substantially lower than bulk. We discuss on the possible mechanisms leading to this remarkable difference of magnetization.

Two theoretical sinusoidal diffractive profile models to build up a trifocal intraocular lens (IOL) are analysed. Topographic features of the diffractive zones such as their shape, step height and radii, as well as the energy efficiency (EE) of the foci, depends on the particular model, and are compared to the ones experimentally measured in a trifocal lens that claims to be designed with a generic sinusoidal diffractive profile: the Acriva Trinova IOL (VSY Biotechnology, The Netherlands). The topography of the IOL is measured by confocal microscopy. The EE is experimentally obtained through-focus with the IOL placed in a model eye. The experimental results match very accurately with one of the theoretical models, the optimum triplicator, once that a spatial shift in the sinusoidal profile is introduced in the model.