R. Ciprian

Growth and characterization of epitaxial Fe-Pt films

The magnetic and structural properties of Fe/sub 53/Pt/sub 47/ deposited by alternated-layer sputtering on MgO (100), heated at temperatures up to T=550/spl deg/C, were investigated. The effect of a subsequent thermal annealing performed at the same temperature was found to be essential for obtaining 10-nm FePt thin films with a high degree of ordering and high squareness.

Effects of deposition temperature and elemental layer thickness on the properties of Fe/Co multilayers grown by molecular beam epitaxy

Fe/Co multilayers were grown at different temperatures up to 200 °C onto MgO-(1 0 0) monocrystalline substrates, varying both the Co and Fe elemental layer thicknesses. All samples show a multilayered structure where the elemental layers are separated by a thin interfacial region which, for high-temperature growths, is constituted by an equiatomic FeCo compound. The multilayers grown at room temperature show an in-plane uniaxial magnetic anisotropy. The increase in the growing temperature determines an improvement of the sample smoothness and the appearance of two preferred in-plane orientations of the easy magnetization axis having different strengths. By increasing the Co layer thickness, the in-plane magnetic behaviour becomes isotropic, while by increasing the Fe layer thickness, an out-of-plane contribution to the magnetization vector is established, which is responsible for the appearance of a well-defined magnetic morphology constituted by stripe-like domains.

Highly coercive L10-FePd thin films grown on MgO single crystal substrates

L10-ordered systems are of great interest from both the technological and research point of view since their high magnetocrystalline anisotropy makes them suitable candidates for future high density recording media. FePd and FePt are isostructural alloys that in their ordered phase show very different magnetic behaviour. In this work ultra-thin films of FePd and FePt films have been grown showing very hard magnetic properties. The coercivity of FePd films grown at 700°C reaches values well above 10 kOe much greater than that obtained in FePt films grown in the same conditions.

Interface Phenomena and Magnetic Properties of Fe/Cr Multilayers

Fe/Cr thin film multilayers were e-beam evaporated in ultra-high vacuum changing the elemental layer thickness while the Fe/Cr thickness ratio was maintained fixed to 2. The magnetic properties were correlated to the sample microstructure and morphology, as a function of the elemental layer thickness. For very low multilayer thickness, the samples are mainly constituted by particles showing both superparamagnetic and ferromagnetic behavior. By increasing the thickness of the multilayer, the superparamagnetic small particles decrease up to vanish, and the magnetic properties become antiferromagnetic. A further increase of the layer thickness determines the formation of low defective layers of pure Fe and Cr intercalated by thin regions of Fe-Cr alloy. The system becomes ferromagnetic with a significant out-of-plane tilting of the magnetization vector which determines a magnetic morphology changing from stripe-57to labyrinth-like configuration.

Phase composition and morphology as a function of depth for boride coatings grown on Fe-Ni alloys

Two Fe-Ni alloys very differing in Ni content, Fe64Ni36 and Fe20Ni80, were borided at 850°C for 8 h using a high boron potential powder medium. On both alloys ~150 μm thick boride coatings grew in the form of two stratified sublayers of different thickness depending on the Ni content of the metal substrate. The outer sublayer mainly consisted of a ternary (Fe,Ni)B compound with small amounts of Ni borides in its outermost region, the inner by a ternary (Fe,Ni)2B compound. It is shown and explained how the same (Fe,Ni)B compound could form on both high-Ni alloys in spite of the considerable difference in Ni content.

On the exchange coupling interaction between Fe and L10-ordered FePd thin films

Hard L10-ordered FePd ultra-thin films were epitaxially grown by means of a molecular beam epitaxy system on MgO-(100) monocrystalline substrates. Because of the very low thickness of the films, small amounts of superparamagnetic L10-FePd particles were also formed on the surface. The magnetic properties of the films are typical of highly coercive systems showing a strong perpendicular anisotropy. These hard films were used for the development of soft/hard exchange-spring magnets, by depositing different thickness of iron. Fe reacts with the surface FePd small particles giving rise to a Fe(Pd) compound with a broad distribution of particle sizes. The resulting systems are bi-layers constituted by a soft Fe(Pd) and a hard L10-FePd layer intercalated by a very thin region of small particles. For soft/hard thickness ratio nominally equal to 1 the magnetic behaviour is typical of a single-phase hard magnet. By increasing the nominal thickness ratio up to 3, the behaviour becomes typical of an exchange-coupled magnet with hysteresis loops characterized by two critical fields.

Magnetic anisotropy and exchange interactions in Fe/Co multilayers grown on different substrates

Fe/Co ultra-thin multilayers were simultaneously e-beam evaporated onto different substrates, varying both the Co and the Fe thickness as well the deposition order. For all the samples a strong uniaxial in-plane anisotropy has been detected. In particular the low intermixing at the interfaces, the adopted growing conditions and the low thickness of the elemental layers allow to obtaining magnetically textured samples also when the starting layer is constituted by Fe. The substrates influence the microstructure of the samples determining the strength of coercivity and the tilting out of the film plane of the easy magnetization axis.

Morphological, Magnetic, and Microstructural Study of Fe/Co Multilayers Grown at Different Temperatures

Co/Fe multilayers were grown onto different substrates by means of a molecular beam epitaxy system equipped with e-guns. The microstructural and magnetic properties were studied as a function of both the growing temperature and the Fe-layer thickness. All the samples grown at room temperature show a magnetic behavior typical of systems having a strong uniaxial in-plane anisotropy. The Fe-layer thickness influences the strength of the in-plane anisotropy. By growing the samples at high temperature, a reduction of the Fe/Co intermixing occurs and the magnetic behavior becomes strongly influenced by the nature and crystallinity of the substrates. In particular, using glass substrates, the in-plane uniaxial anisotropy strengthens, whereas when using MgO monocrystalline substrates, a second in-plane easy magnetization axis establishes perpendicular to the main one. Using naturally oxidized Si substrates, a significant out-of-plane contribution to the anisotropy appears, giving rise to a magnetic behavior controlled by the competition between the perpendicular anisotropy and the demagnetizing field.

Growth and characterization of epitaxial FePt films

FePt films are prepared by RF sputtering at intermediate temperatures (up to 550/spl deg/C) followed by thermal annealing at the same temperature. Structural characterization is then performed by means of X-ray diffraction and transmission electron microscopy. The results indicate that the effect of in-situ annealing after the high-temperature growth turns out to be essential in obtaining well-oriented and highly coercive films. The magnetic properties are studied at room temperature by an alternating gradient force magnetometer.

Magnetic properties of iron doped zirconia as a function of Fe concentration: From ab initio simulations to the growth of thin films by atomic layer deposition and their characterization by synchrotron radiation

The authors investigated the magnetic properties of Fe-doped zirconia, ZrO2:Fe, grown by atomic layer deposition, for different concentrations of Fe dopant, a substitutional impurity to Zr. Their growth recipe allows the deposition of films in which the percentage of Fe, x, ranges from diluted (x  ∼ 1–2 at. %) up to high (x ∼ 25 at. %) concentrations. By x-ray magnetic circular dichroism, the authors carefully analyzed the magnetic moments of these dilute magnetic oxides at low temperature (T = 5 K), determining the best dopant range maximizing the magnetic signal. In particular, the authors found that the magnetic signal decreases as the Fe concentration increases. By comparison with ab initio simulations, the authors enlighten the microscopic mechanisms responsible for this peculiar behavior.