•Co/Gd3Ga5O 12/Y3Fe5O12 heterostructures were grown by laser molecular beam epitaxy.•Selective YIG and Co magnetization curves were measured by MOKE and XMCD techniques.•Clear proximity effects were ...observed in heterostructures with 1 nm thick GGG spacer.•Ferromagnetic interaction between Co and YIG was explained by “orange peal” effect.
Interlayer magnetic coupling has been studied in the epitaxial system consisting of few nanometer thick magnetic layers of cobalt and yttrium iron garnet (YIG) separated by non-magnetic spacers of gadolinium gallium garnet (GGG). The samples were grown by laser molecular beam epitaxy on GGG(1 1 1) substrates. The layer morphology and crystal structure were characterized by atomic force microscopy, X-ray and electron diffraction techniques. MOKE and XMCD methods were applied for element selective study of the magnetization reversal in Co and YIG layers. For the Co/YIG/GGG heterostructures it has been found that magnetization loops of YIG and Co exhibit the same values of coercive field and are of the same shape indicating strong magnetic coupling between Co and YIG layers. In opposite, when YIG and Co are separated by a 1 nm thick GGG spacer layer, the coercive field of Co becomes very different from that of YIG. Moreover the center of YIG loop gets shifted in field whereas the sign and value of this shift depend on the current magnetic state of the Co layer. The magnetic interaction between Co and YIG can be interpreted in the terms of 2–3 Oe magnetic field induced in the YIG layer by the adjacent Co layer. This magnetic field is likely caused by the “orange peel” effect arising due to granular structure of Co layer.
Nanostructured FeO films with an average nanoparticle size of the order of 6–10 nm were fabricated by laser electrodispersion. Annealing at
T
= 300°C in vacuum resulted in the disproportionation of ...FeO particles into Fe
3
O
4
and α-Fe, while the films exhibited a marked crystal orientation (texture with the 111 axis). The coercive force and the saturation magnetization of the synthesized nanostructured Fe
3
O
4
/α-Fe films were as large as ~660 Oe and ~520 emu/cm
3
, respectively. These values are considerably higher than the corresponding parameters of polycrystalline Fe
3
O
4
films.
Laser molecular-beam epitaxy has been employed to obtain layers of yttrium-iron garnet (YIG) Y
3
Fe
5
O
12
on gallium nitride substrates. It was found that there exists a polycrystalline YIG phase ...without admixtures of other structural phases. A magnetic anisotropy of films of the “easy-magnetic plane” type was found. The gyromagnetic ratio and the demagnetizing field 4π
M
S
were calculated.
We investigate the magnetic anisotropy and domain structure of amorphous Tb
x
Co
(1−
x
)
films grown in external in-plane magnetic field by high-frequency ion sputtering. Films with different ...thicknesses 100 and 500 nm and rare-earth element concentrations
x
= 12 % and
x
= 34 % present strong imprinted in-plane uniaxial anisotropy. Measurements of magnetic properties and domain structure imaging were performed by means of longitudinal and polar magneto-optical Kerr effect (MOKE). The coercivity fields increase by an order of magnitude for the higher Tb concentration and increase with film thickness (
H
c
along the hard axis are 495, and 580 Oe, for 100 and 500 nm, with
x
= 34 % and 65, and 95 Oe for 100 and 500 nm with
x
= 12 %, respectively). Polar MOKE measurements revealed the existence of an out-of-plane magnetization component for the films with a Tb concentration of 34 % in lower fields. Large-scale domain structure of TbCo films with imprinted anisotropy was also studied as a function of applied field. Kerr imaging shows a zigzag domain structure of Tb
12
Co
88
films, while no domains were found in Tb
34
Co
66
samples. We also demonstrate that the zigzag angle depends on the film thickness. We suggest that domain structure in these films is determined by the interplay of imprinted and local magnetic anisotropies as well as exchange interaction.
Yttrium iron garnet (YIG) films were grown on GaN substrates using the laser molecular beam epitaxy method. X-ray diffraction data showed polycrystalline YIG layers without additional structural ...modifications. The magnetic properties of the YIG films were studied at room temperature with the aid of a vibration sample magnetometer, the magneto-optical Kerr effect and ferromagnetic resonance methods. 'Easy-plane'-type magnetic anisotropy was found in the films. The gyromagnetic ratio and 4 πMS value were calculated.
► Corrugated surface of substrate affect magnetic anisotropy of Co films. ► Cobalt nanoparticles forms linear chains. ► The anisotropy is measured by LMOKE. ► The anisotropy is due to magnetic dipole ...interaction between nanoparticles.
Cobalt nanoparticle 2D arrays with different effective thicknesses of cobalt layer (2nm<deff<10nm) were grown by molecular beam epitaxy on CaF2(110)/Si(001) and MnF2(110)/CaF2(110)/Si(001) substrates with corrugated morphology of the surface. Surface morphology analysis showed that for effective thickness of cobalt layer deff=5nm the lateral dimensions of cobalt islands are about 5–10nm and the distances between the islands differs in a half along and across the grooves. In both types of the heterostructures the shape of hysteresis loops measured by LMOKE depend on orientation of in-plane magnetic field relative to the direction of the grooves. The azimuthal dependence of coercive field Hc in Co/CaF2(110)/Si(001) structures corresponds to Stoner–Wohlfarth model's predictions, which takes into account the anisotropy of individual particles. In contrast to that, in Co/MnF2(110)/CaF2(110)/Si(001) structures these dependences are analogous to those predicted by the model based on account of magnetic–dipole interaction between particles which are placed in chains (chain-of-spheres-model). Possible explanations of the difference in magnetic anisotropy are suggested.
Combined excitation-emission spectroscopy was carried out to study Eu3+ centers in CaF2:Eu-CdF2 superlattices. Two distinctive centers were observed and assigned as remote (R) and interface (I). The ...energy level of the R center appeared to be close to the cubic center in a bulk crystal and mainly consists of Eu3+ ions located away from the SL boundaries. The relative intensity of the interface centers was very sensitive to the layer thickness and became more prominent in thinner layers indicating it is associated with Eu3+ ions in layers next to the SL boundary. A splitting of the 5D1 manifold indicates the interface center has axial symmetry, which is suggested to come from a charge-compensating electron trapped in the conduction band of CdF2 layer.
Laser spectroscopy technique has been applied for studies of MnF
2 and ZnF
2 layers grown by molecular beam epitaxy on silicon substrates with the use of CaF
2 buffer layer. The films were doped ...during the growth with samarium either from SmF
3 molecular or Sm atomic beams. The excitation wavelength was scanned in the region of
6H
5/2→
4G
5/2 transitions of Sm
3+ as well as near the absorption edge of the Mn
2+ 3d excitons of the tetragonal and orthorhombic phases of MnF
2. The observed emission lines have been assigned to two types of (Sm
3+–F
−) centers in the orthorhombic phase and one in the tetragonal rutile phase of MnF
2. Efficient energy transfer from the host lattice to Sm
3+ centers was observed during excitation into the lowest Mn
2+ absorption band. Similar centers were also found in ZnF
2 epitaxial films, where along with (Sm
3+–F
−) pair centers, an isolated Sm
3+ center with remote charge compensation was observed. Thus it was shown that Sm
3+ ions can be used as efficient luminescent probe for characterization of crystal phase composition in the films as well as the local environment of the dopants.
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