X-ray diffraction and electron microscopy were used to examine the crystal structure features of ultrathin (3–50 nm) yttrium orthoferrite films, obtained by magnetron sputtering of stoichiometric composition target on α-Al2O3 substrates with orientation. The morphology and crystal structure of the films differ significantly depending on their thickness. In the thinnest films, several phases are formed, including yttrium orthoferrite with an orthorhombic crystal lattice (o-YFeO3), yttrium hexaferrite with a hexagonal crystal lattice (h-YFeO3), iron-yttrium garnet (Y3Fe5O12), and iron oxides such as hematite and maghemite. The study examines the local composition and determines the orientation ratios between the crystallized phases and the substrate. The films with a thickness greater than 10 nm predominantly exhibit a highly textured phase of o-YFeO3 with a small admixture of iron-yttrium garnet.

Annotation: Magnetooptical Faraday and Kerr effects are studied in the nanosized BiY2Fe5O12 films within the spectral region of 1.3 eV<E<4.5 eV and magnetic fields of up to 10 kOe. It is shown that the thin-films BiY2Fe5O12 with the thicknesses ranging from 5 to 51 nm obtained by magnetron sputtering on the single-crystalline Gd3Ga5O12 substrates have high magneto-optical quality. The specific Faraday rotation for the nanosized Bi0.5Y1.5Fe5O12-delta films reaches about 140000 deg/cm close to that for bulk BiY2Fe5O12. Meanwhile, the polar Kerr effect reaches about 30 min within the range of 1.6 eV-4.1 eV at the magnetic fields above 2 kOe. It is shown that the strong paramagnetic contribution of Gd3Ga5O12 substrates significantly affects the Faraday and Kerr effect for the films. The defining of magnetooptical parameters and Verdet constant for the Gd3Ga5O12 substrate permitted to separate the substrate contribution and reveal peculiarities of spectral dependences of both Faraday and Kerr effects for magnetic films of various thicknesses. The estimated critical thickness of the film-substrate interface region is as large as 35 lattice constants of BiY2Fe5O12. It is shown that the magnetooptical effects for the thin films with the thickness above the critical one correspond to those for bulk BiY2Fe5O12. For samples with the smallest thicknesses of the film (5 nm) the contributions from magnetically dead and magnetically passive layers lead to a drastic reduction in the observable Faraday and Kerr effects with a dominating contribution from the substrate. The high density of displacement dislocations at the film-substrate interface leads to the decrease the magnetooptical quality of the nanosized films.

Features of the magnetic state of antiferromagnetic YFeO3 films thermally treated in an oxygen atmosphere and air have been studied by nuclear magnetic resonance spectroscopy. A strongly inhomogeneous distribution of local magnetic fields with characteristic scales about the interatomic distance has been revealed. The existence of two magnetically nonequivalent positions of iron ions corresponding to its different valence states has been detected in the YFeO3 films under study. The relation between these nonequivalent positions of iron, as well as the degree of distortion of the crystal lattice, depends on the thermal treatment atmosphere.

The paper studies the influence of the composition of a thin-film composite magnetostrictive ferromagnet on the magnetoelectric effect (ME) in ferromagnet/piezoelectric/ferromagnet laminated trilayers at resonant frequencies. The PZT material was used in the piezoelectric layer. The graded composite magnetostrictive ferromagnet with a thickness gradient of the magnetostriction coefficient was obtained by pulsed laser deposition of thin Fe0.72Ga0.28 or Fe0.62Co0.19Ga0.19 films on the surface of Metglas-type 440A amorphous ribbons. The ME was investigated at resonant frequencies of 3 and 9.32 kHz. It is shown that the maximum ME value increases with frequency. The deposition of magnetostrictive thin films decreases the maximum ME value, but increases the Q-factor. The results can be useful for developing sensors of static and low-frequency magnetic fields for magnetic nondestructive testing applications under resonant excitation conditions.

The paper experimentally demonstrates the possibility of recording low-frequency (20 Hz to 10 kHz) magnetic fields in laminated structures of the composite magnetostrictive thin-film ferromagnet / piezoelectric / magnetostrictive ferromagnet type.Quartz single crystals are used as the piezoelectric material.The composite thin-film-based magnetostrictive ferromagnet is obtained by pulsed laser deposition of magnetostrictive Fe 0.72 Ga 0.28 or Fe 0.62 Co 0.19 Ga 0.19 thin-film layers on the surface of Metglas-type amorphous ribbons.The possibility of detecting both dc and ac magnetic fields in the frequency range from 20 Hz to 10 kHz by measuring the magnetoelectric voltage coefficient (MEVC) in laminated structures is demonstrated experimentally.The influence of the composition of the thin film layer on magnetic noise in the frequency range of 0.5 to 14 Hz is studied.It is shown that the deposition of thin films improves neither the maximum value of MEVC nor the coefficient of linearity at "high" (20 to 50 Oe) magnetic fields in the whole frequency range under study.However, the deposition of Fe 0.62 Co 0.19 Ga 0.19 films enables us to achieve higher coefficients of linearity in the region of zero magnetic fields.Besides, the deposition of thin films increases magnetic noise.The obtained results can be useful in the development of sensors of both dc and ac magnetic fields for nondestructive systems and devices operated at elevated temperatures.

The specific features of dependences of the magnetic anisotropy constants on the thickness of yttrium iron garnet films prepared by pulsed laser deposition were studied. Films with thicknesses of 96–333 nm were produced by pulsed laser evaporation of the target material and deposition onto gadolinium-gallium-garnet substrates with the (111) orientation. The results of an investigation into static magnetic properties showed that the saturation magnetization decreases as the films get thinner. The high-frequency properties were studied by ferromagnetic resonance (FMR). The uniaxial and cubic anisotropy fields and the relaxation parameter were determined by analyzing the angular dependences of the resonance field and the FMR line width. It was found that as the thickness decreases, the strength of the uniaxial anisotropy field increases monotonically, while the cubic anisotropy field decreases and reverses its sign.