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This work focuses on the study of structural and magnetic properties of Mg2+-substituted cobalt nanoferrite (Co1-xMgxFe2O4, 0.0 ≤ x ≤ 1.0). The samples were synthesized by a coprecipitation route and then annealed at 850 °C for 2 h under atmospheric air. The X-ray diffraction patterns show that the samples crystallize in a cubic spinel structure with space group F d 3 ‾ m , and 3% secondary phase was identified as hematite ( R 3 ‾ c ) for x = 1.0. The average crystallite size (D) and the lattice parameter were greatly influenced by Mg content (D decreased from 38 to 20 nm). Transmission electron microscopy investigations revealed that the grains have an almost spherical shape and furthermore that the samples are chemically homogeneous. Magnetic measurements at 5 K revealed a wasp-waist magnetic hysteresis behavior of Co–Mg ferrite. The coercivity of Co0.4Mg0.6Fe2O4 with D = 25 nm was enhanced, with a maximum value of 4000 Oe. The room temperature Mossbauer spectra were fitted with two Zeeman sextets, which reflects the incorporation of Fe3+ in the A and B sublattices of the spinel structure. The hyperfine field of these sites decreases similarly to the saturation magnetization with increasing Mg content. The spectrum corresponding to x = 1.0 was calculated with the help of the hyperfine field distribution. Moreover, Mossbauer spectra, fore x = 0.0 and 1.0 were recorded at 6 and 80 K and were adjusted by the superposition of three sextets: one sextet for the A site and two sextets for the B sites (B1 and B2). The hyperfine parameters such as the hyperfine field and the isomer shift were improved at 6 and 80 K.

Sputtered Tb/Fe multilayers (ρ Tb =0.2–1.9 nm, ρ Fe = 0.2–3.3 nm) have been characterized both by CEMS and the Kerr effect. Saturated Kerr angles υ K vary linearly with the hyperfine field at the iron site, indicating the υ K comes mainly from the iron magnetic moment. All the structural and magnetic results can be interpreted in a (ρ Tb ,ρ Fe ) diagram.

The magnetic and structural transformations in Tb/Fe multilayers irradiated with high energy Pb ions have been studied by 57Fe conversion electron Mossbauer spectrometry. Compositionally modulated amorphous FeTb alloy regions are formed at the interfaces in the vicinity of the ion path, accompanied by a loss of the perpendicular magnetic anisotropy. A phenomenological model, proposed earlier, has been used to explain the evolution of the magnetic anisotropy.

Two bcc-Fe/Tb MLs with t Fe far from and close to the limit of crystallization of Fe layers were irradiated with Xe ions at various fluences and investigated by 57 Fe Mossbauer spectrometry at 300 K. Two structural effects were evidenced: the usual mixing of layers and a demixing of the Fe and Tb atoms at the interfaces. The first process, observed in the two samples, destroys progressively the layered structure and leads to the formation of the corresponding amorphous alloy at high fluence. The second process, observed only at low fluence before the step of mixing for the multilayer close to the limit of crystallization of Fe layers, features the thermal metastability of this multilayer which relaxes towards a minimal energy state. It increases the pure iron part in the center of the iron layers, thus sharpening the interfaces.

Amorphous sputtered Fe/Tb Multilayers were annealed at different temperatures in a high-vacuum furnace and investigated at 300 K by conversion electron Mossbauer spectrometry and by high-angle X-ray diffraction, in order to study the effects of annealing on the structural and magnetic properties. At low annealing temperatures, a demixing process can be observed, which sharpens the interfaces and increases the perpendicular anisotropy. At intermediate temperatures, the mixing of the layers progressively destroys the layered structure and the sample exhibits the magnetic properties of the corresponding amorphous alloy. At higher annealing temperatures, the crystallization of α-Fe is observed.

International audience; Fe layers, 3, 6, 10, and 25 nm thick, were epitaxially deposited by ion-beam sputtering on InGaAs∕InP(100) wafers. For the 3-nm-thick layer, the sample shows a strong in-plane uniaxial magnetic anisotropy along the [110] direction between 5 and 300 K. The 6-nm film exhibits competition between the uniaxial magnetic anisotropy and the magnetic anisotropy of the bulk bcc Fe. The fourfold magnetic anisotropy of the bulk Fe dominates for the 10-nm Fe film. A decrease of the magnetization is observed for the thinner sample as compared to the bulk. This decrease is discussed in terms of Fe thickness, interface effect, diffusion effect, and possible phases at the interface with the semiconductor.

Fe/Tb multilayers with fixed Tb thickness (1.0 nm) and various Fe thicknesses (0.7–2.4 nm) in the domain where both Fe and Tb layers are amorphous, have been investigated by CEMS and magnetic measurements in the 4–300 K range. The results on magnetic anisotropy are interpreted taking into account the composition modulation in the multilayers and the dominant magnetic subnetwork.

UHV evaporated (Fe/Y) n multilayers deposited into a MBE evaporator on MgO substrate were investigated by RHEED, GXRD, high-angle XRD, 57 Fe Mossbauer spectrometry at room temperature, and magnetization measurements at 300 and 5 K. The RHEED study was performed for (Fe 15 nm/Y) bilayers as a function of the Y thickness and for two (Fe/Y) n= 5 multilayers ( t Fe = t Y =0.5 nm and 1.0 nm) to determine the growth and the nature of the interfaces. The GXRD, high-angle XRD, 57 Fe Mossbauer spectrometry at room temperature, and magnetization measurements studies were performed as a function of the Fe layer thickness ( t Fe =0.5–6.0 nm) on (Fe t Fe /Y 1.0 nm) n> 5 multilayers deposited at 300 K. The Mossbauer paramagnetic doublet obtained at 300 K for t Fe =0.5 nm, is characteristic of the Fe–Y interfaces. The crystallization of BCC Fe in the center of the Fe layers occurs for t Fe between 0.5 and 1.0 nm indicating that the Fe–Y interfaces are very sharp compared to other deposited (Fe/Y) multilayers. For (BCC Fe/Y) multilayers, the Mossbauer and the magnetization results indicate that the Fe–Y interfaces thickness remains constant as t Fe increases. In average, only one monolayer of Fe is involved at each Fe–Y interface.

X-ray diffraction, Mossbauer effect and magnetisation investigations have been performed on sputtered Fe40(Al2O3)60 thin films. Ultrafine Fe particles of nanometer size in an amorphous Al2O3 matrix have been formed by annealing in the temperature range from 100°C to 500°C. Their particle sizes, however, show a rather wide distribution. Mossbauer spectra are constituted of both paramagnetic and ferromagnetic contributions. The paramagnetic contribution is associated with small grains of Fe, whereas the magnetic component is contributed by large iron grains. This assumption is supported by the ZFC- and FC-measurements, in which the “blocking” temperatures of 60 and 90 K were evidenced for as-deposited and 200°C-annealed films, respectively.

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Amorphous multilayers with 57 Fe probe layers were irradiated with swift heavy ions and investigated by 57 Fe Conversion Electron Mossbauer Spectroscopy. Partial recrystallization of iron has been evidenced in the amorphous Fe layers. Furthermore, a demixing effect between Fe and Tb atoms is observed at the interfaces. The electronic stopping power threshold value for the recrystallization and the demixing process has been estimated between 5 and 15 keV/nm.

Tb/bcc-Fe evaporated multilayers with 57Fe probe layers were irradiated with swift uranium ions. For the sharp Tb Fe interface, only continuous mixing is observed, but for the diffuse Fe Tb interface, an homogenization is first evidenced at low fluence. The mixing efficiency saturates at high fluence and it still remains a crystallized Fe part. The magnetic anisotropy was reported and interpreted versus the ion fluence.

Amorphous Tb/Fe multilayers were irradiated with Kr, Xe, Pb and U ions at various fluences and investigated by 57 Fe Mossbauer spectrometry at 300 K. Two processes are generally evidenced. The demixtion of Fe and Tb atoms at the interfaces produces an increase of the pure Fe thickness in the center of iron layer. The mixing of layers destroys progressively the layered structure and at high ions fluence the samples exhibit magnetic properties of amorphous alloys. The electronic stopping power threshold of mixing is estimated.