A combined conversion electron and γ-transmission Mössbauer spectroscopy is applied to investigate the differences in the surface and bulk crystallization of the amorphous Fe-M-B-Cu (M: Zr, Ti, Nb, Ta) alloys. It is shown that the surface crystallization occurs at an annealing temperature lower than in the bulk. The nanocrystalline bcc Fe phase is significantly more abundant at the surface than in the bulk in the entire annealing temperature range.

In this work we describe crystallization kinetics as inferred from time-dependent magnetization studies and thermal analysis for an Allied Signal amorphous Fe-based METGLAS® 2605SA-1 alloy and a NANOPERM (Fe88Zr7B4Cu1) alloy. We illustrate and contrast several phenomena important to understanding crystallization kinetics in particular to the NANOPERM alloy system. In METGLAS® 2605SA-1 primary and secondary crystallization events are observed in differential scanning calorimetry data (DSC) at temperatures of 504 °C and 549 °C, respectively for data taken at a 10 °C/min scan rate. Both temperatures are greater than the Curie temperature of the amorphous alloy. For the NANOPERM alloy primary crystallization (as determined from differential thermal analysis (DTA)) occurs at 500 °C and secondary crystallization at 730 °C and M(t) at temperatures near the primary crystallization temperature is dominated (at short times < 1 hour) by the primary crystallization event. Using the Johnson-Mehl-Avrami equation for isothermal transformations and the Kissinger equation for constant heating transformations, we find corresponding models for the crystallization kinetics of the NANOPERM alloy.

Superior soft magnetic properties of nanocrystalline two-phase FeCuNbSiB alloy can only be attainable from a suitably nano-crystallized structure in the amorphous matrix. In this study a thermal-cycling-annealing process was adopted to anneal the amorphous specimens. The crystallization fraction of Fe73.5Cu1Nb3Si13 5B9 ribbons after different annealing was quantitatively measured by a DTA method through the integrated crystallization enthalpy from annealed samples versus that of as-cast amorphous specimen. The crystallization fraction was estimated to be 70 % as the specimen was annealed for 550°C×7.63 ks, the optimal annealing condition. Using this method, the crystallization quantity of the crystallized FeCuNbSiB amorphous alloy was accurately estimated and controlled during nano-crystallization processes.

The radio-frequency collapse of the magnetic hyperfine structure in the Mössbauer spectra is employed to study directly the short range order in amorphous Fe-M-B-Cu (M: Zr, Ti, Ta, Nb, Mo) alloys via the electric quadrupole hyperfine interaction. The shape of the quadrupole splitting distributions obtained from the rf collapsed spectra strongly suggests the existence of two short range orders with a high and low local content of iron. The decrease of boron content in FeZrB alloys leads to a more symmetric local structure experienced by Fe atoms.

Ultrathin ribbons of amorphous Fe83Cu1Nb7B9 obtained by planar flow casting, have been submitted to dc Joule heating in vacuum to develop a nanocrystalline phase. Variations in the initial magnetic permeability as high as 1000 times the as-quenched value have been measured in a wide range of nanocrystalline samples. The magnetoimpedance behavior in the microwave region has been studied as a function of the nanocrystalline state. In this work the intensity of the impedance variation has been related to the samples degree of softness.

Fe/Ce multilayers are magnetically soft with coercive fields of a few Oersteds. In these structures the Ce-5d states are magnetically polarized by hybridization with the 3d states of Fe. The element selectivity of X-ray magnetic circular dichroism (XMCD) is used to measure the magnetization reversal of the Ce-5d states at room temperature. Comparison with the macroscopic magnetization curves studied by the magnetooptical Kerr effect (MOKE) reveal that the ordered Ce-5d moment is not directly coupled to the overall Fe-layer magnetization: the coercitivity of the Ce hysteresis is reduced a factor of two. In view of previous 57Fe Mössbauer spectra this is attributed to an effect of the interface where nominally 1 atomic layer of Fe and Ce are intermixed. Magnetization reversal is initiated in this region due to a reduced magnetocrystalline anisotropy and then propagates into the Fe layers. This interpretation is supported by an experiment on a hydrided multilayer Fe/CeH2.6_6: In this case, there is no intermixing at the interfaces and the magnetization of the Ce-5d electrons follows the Fe-layer magnetization directly.

Epitaxial films of the fcc metals Al, Au, Ag and Ni were grown by physical vapor deposition on Si and Ge (111), (110) and (100) substrates at different deposition temperatures. The epitaxial relationships and morphological features of these films were characterized by transmission electron microscopy and diffraction in plan view and cross section. Ag formed single crystal films on all substrates at all temperatures. Au and Al could be grown as bicrystals, and under some conditions, Al and Ni grew as tricrystal films. The morphological effects of diffusion at the metal/substrate interface are ascribed to diffusion induced grain boundary migration.

In this study, we examine the effects of CrMn/NiAI and Cr/NiAl underlayer structures on the crystalline texture and microstructure of CoCrPt magnetic films using x-ray and electron diffraction. The former underlayer structure was found to induce better CoCrPt (1010) texture. The stress in the CoCrPt layer was measured. The effective in-plane anisotropy energy densities of the CoCrPt films on the above two underlayers were also measured by using out-of-plane torque and Miyajima methods and the result was consistent with the texture analysis.

Planar and cylindrical Co thin films have been obtained by pulsed laser ablation. X-ray diffractograms have shown no crystalline structure for the as-deposited samples, while the 450 °C annealed samples exhibit Co fcc crystalline peaks. The Scanning Tunnelling Microscopy has revealed a small increase of the surface roughness for the annealed films. The Hall effect has been used to determine the value of the spontaneous magnetization, Ms, at room temperature; Ms, = 14 kgauss for the as-deposited sample and Ms, = 17.6 kgauss for the 450 °C annealed sample. From transverse magnetooptic Kerr effect, it has been found that the as-deposited samples exhibit magnetic bistability, with a coercive field, Hc, = 6 0e. The annealed samples also show a bistable behavior until the annealing temperature is 450 °C. Besides, it has been observed an increase of Hc up to = 50 Oe, when the annealing temperature increases. The vibrating sample magnetometry has confirmed these results, showing that the magnetization participating in the magnetooptic effect for these low fields is the total spontaneous magnetization of these samples. Moreover, the cylindrical films exhibit magnetoelastic behavior when they are subjected to angular deformation. It has been found that the saturation magnetostriction constant is negative.

Barium ferrite thin films with excellent perpendicular c-axis orientation were successfully fabricated on Si substrate without any buffer layer. To compensate for possible barium deficiency due to the inter-diffusion between films and substrate, a barium-rich target was used. For a 900 Å-thick film, the perpendicular remanent squareness is about 0.9, while the in-plane remanent squareness is about 0.3. The saturation magnetization (Ms) is about 220 emu/cc, while the coercivity is around 3500 Oe. X-ray diffraction (XRD) results show the (001) perpendicular c-axis texture in the films. It was also found that the rapid thermal annealing conditions greatly affect the magnetic properties of barium ferrite films. With a certain flow rate of oxygen gas in the rapid thermal annealer (RTA), barium ferrite films generally crystallize with good perpendicular c-axis texture. Without oxygen gas, the hexagonal barium ferrite phase fails to develop; instead spinel Fe 30 4 phase forms. The reason for the collapsing of hexagonal barium ferrite texture is thought to be an oxygen deficiency in the barium ferrite films due to the reduction of oxygen in the films during the high temperature annealing.

The growth of FexNy thin films on GaAs, In0.2Ga0.8As, and Si02/Si substrates using an ultra high-vacuum (UHV) deposition chamber equipped with electron cyclotron resonance (ECR) microwave plasma source is presented. The structural properties of the deposited films have been measured using various techniques as x-ray diffraction (XRD), Auger electron spectroscopy (AES), and transmission electron microscopy (TEM). The results of XRD measurements show that the films consist of a combination of α-Fe, α'-Fe, γ-Fe4N, and α”- Fe16N2 phases. The depth profiles, calculated from the Auger peak intensities, show a uniform nitrogen concentration through the films. The TEM reveals a columnar structure of these films. The properties of the different Fe-N layers have been exploited in the fabrication of Fe(N) / FexNy / Fe trilayer structures, where Fe(N) means a slightly nitrogen doped Fe film. The magneto-transport properties of this trilayer structure grown on In0.2Ga0.8As substrates are presented.

The amorphous state of ferromagnetic Fe78Si9B13 (Metglas 2605S-2) and its nanocrystallization were investigated by in situ transmission electron microscope (TEM), Xray diffraction (XRD), Mossbauer spectroscopy (MS), differential scanning calorimeters (DSC) and magnetic moment measurements. The Mössbauer spectrum exhibited an essentially symmetric hyperfine field pattern of 259KOe in as-quenched amorphous state at room temperature. The Curie and crystallization temperature were determined to be Tc=708K and Tx= 803K, respectively. The Tx value was in good agreement with DSC measurement results. The occupied fraction of the nanocrystalline phases of α-Fe(Si) and Fe2B at in situ optimum annealing temperature was about 57% and 43%, respectively. It is notable that the magnetization of the amorphous phase decreases more rapidly with increasing temperature than those of nanocrystalline ferromagnetism, suggesting the presence of the distribution of exchange interaction in the amorphous phase or high metalloid contents.