This paper addresses the time-dependent crystallization process occurring in “bulk” amorphous Co80−xFexB20 (x = 20, 40) metallic ribbons by means of synchrotron x-ray diffraction (SXRD) and transmission electron microscopy. Metallic ribbons, produced via melt-spinning technique, were annealed in-situ, with SXRD patterns collected every 60 s. SXRD reveals that Co40Fe40B20 alloys crystallize from an amorphous structure to a primary bcc α-(Co,Fe) phase, whereas Co60Fe20B20 initially crystallizes into the same bcc α-(Co,Fe) but exhibits cooperative growth of both stable and metastable boride phases later into the hold. Johnson-Mehl-Avrami-Kolmogorov statistics was used on post annealed samples to determine the mechanisms of growth and the activation energy (Ea ) of the α-(Co,Fe) phase. Results indicate that the growth mechanisms are similar for both alloy compositions for all annealing temperatures, with the Avrami exponent of n = 1.51(1) and 2.02(6) for x = 20 and 40, respectively, suggesting one-dimensional growth, with a decreasing nucleation rate. Activation energy for α-(Co,Fe) was determined to be 2.7(1) eV and 2.4(3) eV in x = 20 and 40, respectively, suggesting that those alloys with a lower Co content have a stronger resistance to crystallization. Based on these results, fabrication of CoFeB magnetic tunnel junctions via depositing amorphous layers and subsequently annealing to induce lattice matching presents itself as a viable and efficient method, for increasing the giant magnetoresistance in magnetic tunnel junctions.

Received 15 November 2011DOI:https://doi.org/10.1103/PhysRevB.84.219903©2011 American Physical Society

Standing spin waves in a thin film are used as sensitive probes of interface pinning induced by an antiferromagnet through exchange anisotropy. Using coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin-wave thickness mode in Ni80Fe20/Ir25Mn75 exchange-biased bilayers was studied for a range of Ir25Mn75 thicknesses. We show that pinning of the standing mode can be used to amplify, relative to the fundamental resonance, frequency shifts associated with exchange bias. The shifts provide a unique "fingerprint" of the exchange bias and can be interpreted in terms of an effective ferromagnetic film thickness and ferromagnet-antiferromagnet interface anisotropy. Thermal effects are studied for ultrathin antiferromagnetic Ir25Mn75 thicknesses, and the onset of bias is correlated with changes in the pinning fields. The pinning strength magnitude is found to grow with cooling of the sample, while the effective ferromagnetic film thickness simultaneously decreases. These results suggest that exchange bias involves some deformation of magnetic order in the interface region.

Using spin waves we directly probe the interface of an exchange biased Ni_80Fe_20/Ir_25Mn_75 film which has been modified by the presence of an Au dusting layer. Combining this experimental data with a discretised simulation model, parameters relating to interface exchange coupling and modification of interface magnetisation are determined. Exchange coupling is found to be relatively uniform as gold thickness is increased, and undergoes a sudden drop at 1.5Å of gold. Interface magnetisation decreases as a function of the gold dusting thickness. Antiparallel alignment of the ferromagnet and antiferromagnet supress the interface magnetisation compared to when they are in parallel alignment. These findings imply that the interface region has specific magnetisation states which depend on the ferromagnet orientation.

Broadband ferromagnetic resonance responses for metallic single-layer and bilayer magnetic films with total thicknesses smaller than the microwave magnetic skin depth have been studied. Two different types of microwave stripline transducers were used to excite and detect magnetization precession: a coplanar waveguide and a microstrip line both with characteristic width larger than the free propagation path for traveling spin waves along the film. Both transducers show efficient excitation of higher-order standing spin wave modes across the film thickness in samples 30–91 nm thick. The ratio of amplitudes of the first standing spin wave to the fundamental resonant mode is independent of frequency for single-layer permalloy films. In contrast, we find a strong variation in the amplitudes with frequency for cobalt–Permalloy bilayers and the ratio is strongly dependent on the ordering of layers with respect to a stripline transducer. Most importantly, cavity ferromagnetic resonance measurements on the same samples show considerably weaker amplitudes for the standing spin waves. All experimental data are consistent with expected effects of eddy currents in films with thicknesses below the microwave magnetic skin depth. Finally, conditions for observing eddy current effects in different types of experiments are critically examined.

A standard part of vitrectomy surgery is to inject a bubble of gas into the eye, and an important question for the surgeon and patient alike is to know the volume of the bubble and how long it is likely to last. A related question of considerable importance is the mechanism by which it is absorbed. In this paper, we show how to use patients' measurements of the daily variation of their far points to calculate the changing volume of the bubble and hence the rate of gas absorption throughout the post-operative period. The results show that the rate of absorption contains a term in time squared, indicative of absorption through the exposed surface area of the aqueous fluid rather than via the exposed retina.

A series of bulk ternary amorphous alloys of Pd100−3 x Ni2 x P x were prepared and their amorphicity checked by X-ray diffraction (XRD) and neutron scattering. Auger parameters of these alloys have been derived from X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectra (AES). Experiments of XPS and AES on each elemental metal and Ni2P were also performed for comparison. The results show a clear compositional dependence for the 3d binding energies and the MNN Auger energies of Pd on alloying, while Ni 2p core levels and the Ni LMM Auger lines show a weaker variation. Analysis of the data using “excited atom” models indicates electron transfer from Pd, with P carrying negative charge, but the differences in behaviour of the two metallic species suggests that covalent bonding changes may be significant.

A quaternary amorphous alloy Pd40Ni40B10P10 was prepared in bulk form without the use of B2O3 flux and compared with its ternary counterpart, Pd40Ni40P20. Neutron and X-ray diffraction (XRD) were employed to check the amorphicity of the samples, and differential scanning calorimetry (DSC) was used to study the thermal stability of the alloy. The electronic structures of the two alloys were studied experimentally by X-ray photoelectron spectroscopy (XPS), and compared with experiments on the pure metals, Pd and Ni. The results suggest that, rather than being precipitated, boron atoms have been incorporated into the alloy as a replacement for phosphorus. The electronic structure of the valence band is also similar in the two alloys. With the addition of boron, glass-forming ability is demonstrated without the need for any fluxing compound.

Zero-field magnetic viscosity measurements at low temperatures were made on a series of Pd40Ni40−xFexP20 (x=10–20) samples in order to determine the apparent magnetic-moment-weighted energy barrier distributions for these spin-glass alloys. The distributions observed are best described by a stretched exponential in the form of a truncated Lévy flight distribution. This form suggests a hierarchical landscape of apparent energy barriers arising from interactions between randomly oriented magnetic clusters within the material. The degree of stretching of the exponential form of the energy barrier distributions is found to increase with decreasing iron concentration.

The magnetic properties of epitaxial Fe films on GaAs in the range of the first few monolayers have been the subject of a considerable number of investigations in recent years. The absence of magnetic signatures at room temperature has been attributed to the existence of a magnetic ‘dead’ layer as well as superparamagnetism. By examining the temperature dependence of the magnetic linear dichroism of the Fe core level photoelectrons, we found a ferromagnetic regime with a Curie temperature, Tc substantially lower than room temperature, e.g., a Tc of about 240K for thin films of a nominal thickness of 0.9nm. The values of Curie temperature were sensitive to the initial GaAs substrate conditions and the thickness of the Fe over-layer with a layer of thickness of 1.25nm showing a Tc above room temperature. The data suggest that the thin Fe films on GaAs(001) may have ferromagnetic character at an earlier stage of growth than previously expected, although a weaker exchange interaction in the films leads to a substantial reduction in Curie temperature.

Zero and applied field Mössbauer spectroscopy has been used to study the magnetic properties of melt-spun amorphous Pd40Ni22.5Fe17.5P20. It is shown that there are marked similarities in the magnetic properties of bulk and melt-spun amorphous material. The superparamagnet to induced-ferromagnet to spin glass transitions reported for bulk a-Pd40Ni22.5Fe17.5P20 also occur in the melt-spun material and can be characterized by Mössbauer spectroscopy.

Ternary and quaternary bulk amorphous Pd-Ni-P and Pd-Ni-Fe-P alloys were prepared by fast quenching in water. X-ray photoemission spectra of Pd-Ni-P have previously been measured by Alamgir et al. (Phil. Mag. B 79, 239 (1999)). These results have been extended by (a) measuring the Auger spectra and the Auger parameters of key elements, (b) cross correlating the data with PdNi binaries, and (c) investigating the effects of adding Fe. It is shown that the Auger parameters change systematically across the composition range and the results are discussed in terms of possible charge transfer, changes in d-band character, and covalent bonding.

A ballistic electron emission microscopy facility has been used to investigate hot electron transport through Au/M/Au and Au/M thin films (M = Fe, Co) grown on GaAs(100) substrates. The hot electron attenuation through the Au/Fe/Au trilayer roughly exhibited an exponential relationship with Fe interlayer thickness. Two values of Fe thickness (0.4 and 0.85 nm) were used to compare the differences between Fe embedded at the centre of the Au layer and Fe at the metal–semiconductor interface. For the thicker Fe layer, there is a large difference in terms of the transmitted ballistic electrons between the two structures, with the 'at-interface' structure exhibiting substantially increased transmission. This difference was not found in the Au/Co system with comparable Co thickness. The results suggest that the behaviour of transmitted hot electrons is dominated by the formation of the continuous metal layers with strong scattering at the metal–metal interfaces.

Thin epitaxial Fe films were grown on singular and vicinal GaAs(001) substrates, and their magnetic and electronic structures were investigated by synchrotron-based spin-resolved and spin-integrated photoelectron spectroscopy with different Fe thickness. There were two types of substrates: one was a Si-doped n-type GaAs(001) surface with doping concentration of 2 × 1018 cm -3 (singular substrate), and the other was orientated by 3° toward the (111)A direction (vicinal substrate). Spin polarization of the secondary electron peak at different growth stages of Fe coverage for the singular substrate sample and the vicinal one were measured. In the case of singular substrates, there was a dependence of their initial surface reconstruction, which is associated with complex domain structure, while no such the dependence was observed in the case of vicinal substrates. The result from the vicinal sample suggests the geometrical influence of the initial surface stoichiometry of the substrate.

Fe films were deposited on either a heated GaAs(100) substrate at 200°C or a GaAs(100) substrate with a 5Å Au buffer layer in ultrahigh vacuum by molecular beam epitaxy. In order to understand the influence of the heating process and the buffer layer on the magnetic properties, spin polarisation of secondary electrons was investigated. Photoelectron spectroscopes of Fe 3p, Ga 3d and As 3d core levels were used as tools to explain the magnetic behaviour. It is found that according to preparation processes, the magnetic properties of the Fe/GaAs(100) samples could be due to either the formation of FeGaAs compounds or superparamagnetism in the first several monolayers (MLs). Furthermore, neither treatment greatly improved sample properties.

Ultrathin Fe films were epitaxially grown on Ga- and As-terminated GaAs(1 0 0) at room temperature by molecular beam epitaxy. The spin polarisation was studied by synchrotron-based photoelectron spectroscopy (PES). Magnetically dead layers of a few A thickness were observed and the behaviour is attributed to the superparamagnetic phase rather than the formation of nonferromagnetic compounds. For Fe on the Ga-terminated substrate, the spin polarisation increased abruptly and then remained at a constant value when the film was deposited in thickness. In contrast, Fe grown on the As-terminated GaAs(1 0 0) substrate reveals a variable behaviour of spin polarisation with two spin polarisation maximal, along with increasing the thickness of Fe coverlayers. The underlying decreases in the spin polarisation may be attributed to structural changes of Fe coverlayers, related to the different ternary metastable phases. (C) 2002 Elsevier Science B.V. All rights reserved.

The boron contribution to the total spin moment in the amorphous alloys Fe1-xBx (x= 0.2,0.23) has been determined using magnetic Compton scattering. The magnitude of the induced boron moment was found to be approximate to- 0.04 mu (B) per formula unit which is a factor of approximate to2 less than that suggested by supercell linearized muffin-tin orbital electronic structure calculations.

Thin epitaxial Fe films have been grown on vicinal GaAs(001) substrates and their remanent magnetic properties and the degree of substrate atom diffusion investigated using synchrotron-based photoelectron spectroscopy. The vicinal Fe films, though exhibiting greater As diffusion than their singular homologues, displayed better film quality both from the structural and the magnetic points of view. The spin-resolved valence spectra of the vicinal films resemble those for crystalline bulk Fe at lower film thicknesses than for singular films.