Thin magnetic layers have been prepared by pulsed-laser deposition from targets of the orthoferrites: ${\mathrm{DyFeO}}_{\mathrm{3}},$ ${\mathrm{GdFeO}}_{\mathrm{3}},$ ${\mathrm{SmFeO}}_{\mathrm{3}},$ and ${\mathrm{YFeO}}_{\mathrm{3}}.$ All layers were deposited onto quartz substrates at a temperature of 450 °C under high-vacuum conditions, i.e., in the absence of additional oxygen. The as-grown films show evidence of the following phases: ${\mathrm{RFeO}}_{\mathrm{3}},$ ${\mathrm{R}}_{\mathrm{3}}{\mathrm{Fe}}_{\mathrm{5}}{\mathrm{O}}_{\mathrm{12}},$ ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{4}},$ and ${\mathrm{R}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}},$ where $\mathrm{R=Dy},$ Gd, Sm, and Y. The magnetic properties of these films have been investigated using superconducting quantum interference device magnetometry and magneto-optic (Faraday rotation) measurements taken before and after annealing. These studies reveal that the orthoferrite phase is almost completely (>90%) recovered after an annealing treatment at 860 °C for 1 h. We also report on the temperature dependence of the Faraday rotation for these orthoferrites in the temperature range 25–250 °C.

The present study investigates the magnetic properties of spherical monodispersed maghemite (γ-Fe₂O₃) nanoparticles coated with multiple silica (SiO₂) layers of different thicknesses, forming core-shell multifunctional nanomaterials. This study was performed using a combination of local probe techniques (Mössbauer spectrometry) and magnetization measurements. At room temperature, both techniques confirm the superparamagnetic state of the samples, even after being coated with the SiO₂ shells. The zero-field-cooling–field-cooling magnetization curves of the silica-coated γ-Fe₂O₃ nanomaterials with different shell thicknesses allow the evaluation of the intensity of the interparticle dipole–dipole interactions. We estimate the interparticle energy within the framework of dipolar interaction models and relate it with the hyperfine parameters. We further observe that this dipole–dipole interaction increases the superparamagnetic energy barrier, which largely depends on the interparticle distance. Finally, we consider the effect of spin canting at the surface (“dead layer”) of uncoated γ-Fe₂O₃ nanoparticles manifested by a layer of ∼0.5(1) nm.

We demonstrate how controlled changes in oxygen stoichiometry tune the magnetic properties and the superexchange interaction, thus providing a simple and efficient method to elaborate magnetic oxides with strongly modified magnetic and semiconductor properties. Structural and magnetic properties of the model system of yttrium iron garnet (YIG) thin films were tuned by controlling oxygen stoichiometry. The YIG phase diagram has been explored by creating cation and oxygen vacancies during film growth by pulsed laser deposition. Especially, unexplored in thermodynamic equilibrium growth conditions, excess oxygen stoichiometry in a YIG unit cell was investigated: a significant increase of Curie temperature $(+10\%)$ and magnetization $(+20\%)$ were observed. These changes are understood in the framework of a microscopic model implying the formation of ${\mathrm{Fe}}^{4+}$ and ${\mathrm{Fe}}^{2+}$ in the films with oxygen excess and vacancies, respectively.

Iron-carbon nanocomposites have been elaborated by means of a simple chemical procedure based on in situ synthesis of iron nanoparticles within the nanopores of an activated carbon. The Fe nanoparticles present a broad particle-size distribution (5\char21{}40 nm). A combined structural and magnetic study seems to suggest that most of the nanoparticles of mean size $\sim${}15$\hskip0.3em${}nm have exotic ``onionlike'' core-shell morphology of $\gamma${}-Fe nucleus surrounded by a concentric double shell of $\alpha${}-Fe and maghemitelike oxide. The true nature of Fe-oxide was successfully evidenced through room temperature x-ray absorption spectroscopy. The whole system does not reach a fully superparamagnetic regime even at 750 K, probably due to higher blocking temperatures for the largest nanoparticles. M\"ossbauer spectrometry indicates that low temperature para-to-antiferromagnetic transition for the $\gamma${}-Fe phase cannot be discarded. In addition, the external Fe-oxide shell exhibits spin-glass behavior giving rise to the freezing of its magnetic moments at low temperatures. Hence, we propose a competing double magnetic coupling: (i) the oxide shell/$\alpha${}-Fe interaction and (ii) the possible antiferromagnetic coupling between $\gamma${}-Fe nucleus and $\alpha${}-Fe layer; as being both responsible for the observed exchange bias effect at T=5$\hskip0.3em${}K (Hex$\approx${}150$\hskip0.3em${}Oe).

We present results of ferromagnetic resonance measurements on the alloy ${\mathrm{Fe}}_{87}{\mathrm{Zr}}_6{\mathrm{B}}_6\mathrm{Cu}.$ These show the changes occurring in the sample, both magnetically and structurally, during the crystallization process. In this alloy the amorphous phase gradually crystallizes, forming nanocrystallites of α-Fe in a remaining ferromagnetic amorphous matrix. Results show evidence of a disordered and Fe-rich interphase region surrounding the Fe crystallites. This interphase region initially grows along with the growth of the Fe nanocrystals. However, in the latter stages of the Fe nanocrystallization, this phase also crystallizes into the Fe phase and other crystalline phases, and disappears at the end of the Fe crystallization and the beginning of second crystallization. Evidence of an interface localized spin wave mode at the boundary between the amorphous ferromagnetic and Fe phases in the early stages of crystallization is also observed. At higher annealing temperatures, we observe another resonance absorption feature. This is due to the onset of the second stage of crystallization, where FeZr and iron-boride phases form. The results of the ferromagnetic resonance are analyzed in a multiphase regime, where the importance of the magnetic coupling between the various magnetic phases is evident. A minimum of the in-plane anisotropy is found to coincide with the softest magnetic properties of this alloy.