Fe-Zr Glasses Research Articles

Complex Study of H-Induced Structural Rearrangements in FeZr Glasses

Microstructural changes and relaxation processes were examined in Fe-Zr based rapidly solidified samples. These phenomena occur far below crystallization temperature in the course of heat treatment, or even at room temperature, induced by absorbed hydrogen.

A polarised neutron scattering study of two samples of Fe 90Zr 10

The absolute spin-dependent cross-sections of two samples of the ferromagnetic metallic glass Fe 90Zr 10 have been measured by polarised neutron scattering to investigate the presence of non-collinear ferromagnetism. The samples were made by conventional chill-block melt spinning in Sheffield and in Budapest. They were examined at 135 K and in 2 T on the IN20 spectrometer at ILL, Grenoble, and were supported by SQUID magnetometer measurements. The Budapest sample was found to be a collinear ferromagnet but the Sheffield sample has a non-collinear structure. The magnetic structures of these glasses may therefore depend more sensitively on their preparation than has previously been supposed and non-collinear ferromagnetism may not be an intrinsic property of these FeZr glasses.

Magnetic and transport properties of Fe - Zr - B - (Cu) amorphous alloys

FeZrB metallic glasses present magnetic properties that are enhanced compared to the pure FeZr ones. In particular, a large increase of the Curie temperature has been found. Magnetic and Mössbauer measurements show a decrease of the spin-glass character and a parallel homogenization of the hyperfine-field distribution as the boron concentration increases. Resistivity versus temperature measurements show a change in behaviour with B content: in the samples with small amounts of boron, a minimum in the resistivity versus temperature curves appears near the Curie temperature, while samples with high boron content show a low-temperature minimum, characteristic of most metallic glasses. The analysis of the results suggests that the evolution of the magnetic behaviour is related to changes in the density of states at the Fermi level, rather than to changes in the Fe - Fe distances. This is in agreement with published data on the specific heat of FeZr and FeB glasses. The influence of boron is shown to greatly enhance the weak itinerant ferromagnetism of FeZr glasses, leading to stronger ferromagnetic behaviour. The characteristic features of the resistivity are analysed in terms of localization effects on the conduction electrons, which extend to higher temperatures in the low-boron-content alloys.

Annealing and magnetic field effects on the resistivity of Fe-rich FeZr glasses

Electrical resistivity at zero and applied magnetic fields has been measured in as-quenched and annealed Fe 91Zr 9 and Fe 90Zr 10 amorphous alloys between 4 and 320 K. Fe 91Zr 9 remained amorphous after annealing at 400 K (1 h) while in Fe 90Zr 10, traces of crystallites were observed. Similar annealings at 600 K were sufficient to crystallize both alloys, with α-Fe as the main product. A.c. susceptibility shows small changes in the Curie and spin-glass temperatures upon annealing. The resistivity displays a minimum at high temperatures (≅ 250 K), slightly influenced by a magnetic field and thermal treatment. The resistivity is a competition of contributions in which the structure plays the most important role. The presence of magnetic inhomogeneities could also favor an enhanced electronic localization.

Enhancement of superconductivity in relaxed Fe-Zr metallic glasses

The effects of irreversible structural relaxation on the superconducting transition temperature, T c, for Fe x Zr 100− x metallic glasses in the range 20 <- x <- 33 are studied. The samples were characterized by X-ray diffractometry and differential scanning calorimetry. Magnetic susceptibility, upper critical field, and superconducting transition temperature were measured for as-made and relaxed Zr-rich compositions. The results show an unusual increase in superconducting transition temperature upon thermal annealing which was not observed previously in any other metallic glass system. This phenomenon is due to the presence of spin fluctuations in Fe-Zr glasses. A theoretical basis for this T c enhancement is provided by analyzing the experimental data using the modified form of the McMillan equation together with the expression for the Stoner enhanced magnetic susceptibility.

Metallic glasses: structure and properties

The experimental determination of the structures of metallic alloy glasses and the modelling of their structures are reviewed. Some current issues in metallic glass research are discussed, including structural simulation by computer methods and the subject of structural anisotropy in metallic glass ribbons and wires. The different types of magnetic order which can exist in metallic glasses are discussed, using the example of Fe-Zr glasses.

Tensile stress dependence of the Curie temperature and hyperfine field in Fe-Zr-B-(Cu) amorphous alloys.

FeZrB(Cu) metallic glasses present the same Invar (like) properties as the pure FeZr ones, in particular a large dependence of the Curie temperature on pressure. Magnetic and M\ossbauer measurements show a decrease of the Invar character as the boron concentration increases, with a linear relationship between the change of Curie temperature per unit stress and the reciprocal of the Curie temperature itself. The influence of boron is shown to greatly enhance the weak itinerant ferromagnetism of FeZr glasses leading to stronger ferromagnetic behavior. \textcopyright{} 1996 The American Physical Society.

Diffusion in amorphous metallic alloys – experiments, molecular-dynamics simulations, interpretation

After a brief description of the experimental technique used in the authors' diffusion studies of metallic glasses, a representative selection of their self-diffusivity data referring to both the unrelaxed and the relaxed glassy state is presented. On the basis of these observations a model of the diffusion mechanisms operating in metallic glasses is developed and considerably refined with the aid of what has been learnt on diffusive atomic-displacement mechanisms in Fe-Zr glasses from molecular-dynamics simulations. Finally, the strength of these ideas is demonstrated by straightforwardly explaining the extraordinary diffusion-enhancement behaviour of metallic glass under light-ion bombardment and by elucidating the diffusion mechanisms in supercooled molten alloys just above the glass transition temperature.

Electrical resistivity of Fe-Zr glasses from 4.2 to 1100 K

The results of electrical resistivity ϱ( T) measurements on Fe-rich Fe-Zr glasses in a wide temperature range are presented. The ϱ( T) data show minima at temperatures close to the Curie temperature ( T c). A change of slope around 600 K, resembling the behaviour of the Fe-Zr-Cu-B nanocrystalline alloy, is caused by the crystallisation process. An evaluation of various contributions to electrical resistivity reveals that the contribution due to the magnetic scattering is masked by electron-phonon, quantum interference and pseudo-Kondo scattering processes.

Linear and non-linear magnetic response of potentially re-entrant Fe-Zr glasses

Detailed measurements are presented of the field and temperature dependent AC susceptibility of a number of FeZr metallic glasses. By following the behaviour of the 'cross-over' line, the presence of a paramagnetic to ferromagnetic transition below room temperature in this system is confirmed; the asymptotic exponent values characterizing this transition display near Heisenberg-like values (for the index delta , measurements extend to much lower fields than previous studies), although complications arising from anisotropy (most probably spin-orbit coupling) are also revealed. For the first time, the leading term in the non-linear response is shown to display a distinct anomaly at low temperatures. Although not divergent (as in Ising model predictions) the temperature at which this anomaly occurs in the 8 at.% Zr sample agrees with the transverse spin-freezing temperature estimated recently from in-field Mossbauer measurements. While detailed realistic three-dimensional model predictions describing sequential phase transitions in systems with competing exchange interactions are currently unavailable, the present data, nevertheless, support the possibility of a second 're-entrant' transition in this system.

Pressure dependence of spin fluctuations in metallic glasses Ni25Zr75 and Fe100-xZrx (x=75,80).

The superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ of metallic glasses ${\mathrm{Fe}}_{20}$${\mathrm{Zr}}_{80}$, ${\mathrm{Fe}}_{25}$${\mathrm{Zr}}_{75}$, and ${\mathrm{Cu}}_{25}$${\mathrm{Zr}}_{75}$ were measured under quasihydrostatic pressure up to 10 GPa. The volume (pressure) dependence of the electron-phonon coupling parameter, ${\ensuremath{\lambda}}_{\mathit{e}\mathrm{\ensuremath{-}}\mathrm{ph}}$, for ${\mathrm{Cu}}_{25}$${\mathrm{Zr}}_{75}$ was calculated using the McMillan equation. Using this volume dependence of ${\ensuremath{\lambda}}_{\mathit{e}\mathrm{\ensuremath{-}}\mathrm{ph}}$ and the modified McMillan equation, which incorporates spin fluctuations, we determined the volume dependence of the spin-fluctuation parameter, ${\ensuremath{\lambda}}_{\mathrm{SF}}$, in ${\mathrm{Ni}}_{25}$${\mathrm{Zr}}_{75}$ and ${\mathrm{Fe}}_{100\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Zr}}_{\mathit{x}}$ (x=80, 75). It was found that with increasing pressure spin fluctuations are suppressed at a faster rate in ${\mathrm{Fe}}_{100\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Zr}}_{\mathit{x}}$ as the Fe concentration is increased. The rate of suppression of spin fluctuations with pressure was also found to be higher in the Fe-Zr glasses than in Ni-Zr glasses of similar composition.

Hall effect of sputtered NiZr and CoZr metallic glasses near the critical magnetic concentration

With increasing 3d component, the 3d transition-metal Zr amorphous alloys undergo a transition to ferromagnetism at xc=88 at. % Ni, 62 at. % Co, and 38 at. % Fe, respectively. The first two compositions are outside the range of stable melt-spun glasses, but can be prepared by sputtering. In this paper, we present Hall data for sputtered NiZr and CoZr alloys in the vicinity of the critical magnetic composition. For the ferromagnetic glasses, x&amp;gt;xc, the alloys are magnetically soft. Although the NiZr alloys are quite weak magnetically [μ0M(T=0)=0.15 T at 90 at. %], the extraordinary Hall coefficient is very large (Rs=−0.67×10−7 m3/C for the same alloy). In the Co glasses, Rs is positive, but of the same magnitude even though the magnetism is considerably stronger. In the paramagnetic range x&amp;lt;xc, the rapid change in ordinary Hall coefficient close to the critical concentration for ferromagnetism indicates the presence of spin fluctuations, as has been found for the melt-spun FeZr glasses.

Structure analyses of amorphous melt-spun FeZr(B, Si) alloys and mechanically alloyed FeZr powders

Melt-spun amorphous zirconium-rich FeZr alloys with metalloid additions (B, Si) and mechanically alloyed amorphous FeZr powders were investigated by X-ray diffraction and Mössbauer spectroscopy. The comparison of the radial distribution functions G(r) of ternary FeZr(B, Si) alloys with the data for binary FeZr glasses establishes the influence of boron and silicon additions on the structure of the amorphous state. Moreover, in (Fe 24Zr 76)-B alloys, an increasing boron content strongly influences the crystallization behaviour and leads to a stabilization of the glass. Whereas the G(r) of the as-prepared mechanically alloyed Fe 30Zr 70 powder is similar to that of corresponding melt-spun FeZr ribbons, a relaxation treatment at 150°C causes significant changes in G(r) of the Fe 30Zr 70 powder. The crystallization behaviour of this powder differs from that of zirconium-rich melt-spun FeZr ribbons; Zr 2Fe, a well-known metastable phase identified in the crystallization sequence of melt-quenched glasses, does not occur in the powder samples.

Crystallization characteristics of Fe-Zr glasses around the composition Fe90Zr10

Crystallization characteristics of Fe-Zr glasses around the composition Fe90Zr10

Mössbauer effect on mechanically alloyed Fe-Zr glasses

Amorphous Fe-Zr powders have been prepared by mechanical alloying in a powder mill and studied by means of Mössbauer spectroscopy. It is shown, that, within the glass-forming range from about 30 to 78 at. % Fe, the local structure of the mechanically alloyed samples, detected by the Mössbauer effect, is the same as in the corresponding melt-spun or sputtered samples. The existence of a two-phase region above 78 at. % Fe between an amorphous phase and crystalline Fe confirms that amorphization by mechanical alloying is a metastable equilibrium process. There is evidence that mechanical alloying enhances the Zr solubility in Fe up to 5 at. %.

Magnetic properties of iron-rich Fe-Zr glasses.

Magnetic properties of iron-rich Fe-Zr glasses.

Concentration and temperature dependence of the Hall resistivity in FeZr glasses

Hall resistivity measurements are reported for amorphous FexZr1−x alloys near the critical concentration, xc =0.37, for the onset of ferromagnetism. At room temperature, the Hall coefficient RH is positive and grows systematically with Fe concentration as xc is approached from the paramagnetic side. The temperature dependence of RH follows a Curie-like variation whose coefficient diverges at xc. In the ferromagnetic regime, the spontaneous Hall coefficient is extremely large, leading to the conclusion that the side-jump mechanism is responsible for the magnetic contribution. Furthermore, the dependence of RH on susceptibility in the two regimes suggests that this same side-jump term is also responsible for the positive Hall coefficient in the nonmagnetic glasses.

Local Mn moment in amorphous Mn-Zr alloys

While Ni, Co, and Fe display no local magnetic moment when alloyed with Zr in metallic glasses, Mn has a local moment in Mn-Zr, Mn-Zr-Cu, and Mn-Zr-Ni alloys. The moment decreases as Mn increases from 1 to 67 at.% as a result of increasing antiferromagnetic order and no spin-glass interaction could be detected. The Mn moment results in the disappearance of superconductivity at \ensuremath{\simeq}2 at.% Mn while Ni-Zr and Fe-Zr glasses remain superconducting up to 60 at.% Ni and 28 at.% Fe. The superconducting properties of the host amorphous Zr-Ni and Zr-Cu films were similar to those of glasses obtained by melt spinning.