Amorphous Fe-Zr Research Articles

Effects of hydrogen implantation on the magnetocaloric properties of amorphous FeZr films

We report on the effects of H-implantation on the magnetic and magnetocaloric properties of amorphous FeZr films. Arrott plots reveal a second order ferromagnetic to paramagnetic phase transition for the as-grown and H-implanted films, with an increase in TC from 160 to 200 K upon implantation. The maximum change in magnetic entropy (-ΔSM) increases from 0.66 to 0.77J/kgK for a field change μ0ΔH = 1.5T, as well as the relative cooling power (RCP) values were improved from 84.5 to 108.6J/kg. This improvement was attributed to the increase in magnetization and chemical inhomogeneity induced by the implantation process. The increase in the chemical inhomogeneity was supported by the determination of the local exponent n extracted from the slope of Ln(−ΔSM) as a function of Ln(μ0H), which is line with the simulated depth profile of hydrogen atoms through the FeZr film.

Study of the low-field irreversibility line in the transverse component spin-glass phase of the amorphous Fe90Zr10 alloy

Amorphous FexZr100−x alloys display a complex magnetic phase diagram, particularly in the range 89% ≲ x ≲ 93% in which the phase transition from the paramagnetic to a soft ferromagnetic (FM) state at a critical temperature Tc precedes a second transition at Txy < Tc to a transverse spin-glass (SG) phase, with frozen spin components transverse to the magnetization. The softness of the FM phase and the coexistence of FM and SG orderings complicate exploring the low-temperature and low-field critical properties of the glassy transition. Here we study the irreversibility Almeida-Thouless (AT) line that marks the onset of the transverse SG phase in the Fe90Zr10 alloy in the low-field regime up to H = 60 Oe. While ZFC measurements give rise to an AT exponent ϕ = 4.6, similar to that of another amorphous FM compound with random local anisotropy, the induction of magnetic shiftings upon cooling the sample in a large field, − 85 kOe, displaces down the AT line and separates it into two distinct regimes: one also with ϕ = 4.6 for H above 20 Oe, nearly corresponding to the typical field to flip the remanent magnetization, and a new second regime at lower H, with field-induced remanent clusters and exponent ϕ = 3.6 that approaches the mean-field value ϕ = 3. Our findings are discussed on the light of the results from a random nonuniform anisotropy model with FM exchange interactions, which also reported the existence of a two-regimes scenario in the AT line with similar exponents.

The impact of nanoscale compositional variation on the properties of amorphous alloys

The atomic distribution in amorphous FeZr alloys is found to be close to random, nevertheless, the composition can not be viewed as being homogenous at the nm-scale. The spatial variation of the local composition is identified as the root of the unusual magnetic properties in amorphous hbox {Fe}_{1-x}hbox {Zr}_{x} alloys. The findings are discussed and generalised with respect to the physical properties of amorphous and crystalline materials.

Amorphous FeZr metal for multi-functional sensor in electronic skin

The composition of an amorphous metal, which is well known for having no slip plane or slip direction, can be tailored for enhanced strength and a lower Young’s modulus under mechanical stress. Unlike crystalline metals, elastic amorphous metals can, in principle, be used as a flexible electrode in soft, wearable electronics. A metal with a lattice structure absorbs external energy, which causes structural deformations, while an amorphous metal does not absorb energy. Therefore, amorphous metals have excellent mechanical properties that can overcome the limitations of crystalline metals. However, voids inside such metals are easily formed according to Thornton’s model, which results in the formation of mesoporous (10–50 nm) rods due to the spatial separation of metal atoms. We eliminated the porosity in amorphous metals by controlling the kinetic energy of sputtered metal atoms and ions. Optimized Fe33Zr67 has an amorphous structure with a strength of 2.88 GPa and a Young’s modulus of 76.6 GPa. With this amorphous metal, we fabricated a stretchable and multi-functional sensor for electronic skin that enables the detection of pressure, temperature and light and also serves as a heater. In this work, we demonstrate the feasibility of the amorphous metal Fe33Zr67 in soft electronics for use in various industrial applications.

Magnetic behavior of amorphous Fe–Zr thin films sputtered at different Ar pressures

Abstract Amorphous Fe–Zr thin films with similar compositions exhibit a considerable change in their magnetic behaviors when they are sputtered at different Ar pressures. The change is well explained by a parameter – the SPM ratio – devised in this study, which is defined as the ratio of the magnetization due to the superparamagnetic behavior to the saturation magnetization. The change in the magnetic behavior of thin films with 40–70 at.% Fe depends on an increase in the SPM ratio, and it is more prominent at higher Fe contents; for example, the SPM ratio of a thin film with ∼60 at.% Fe increases from ∼0 to 0.69 with increasing Ar pressure from 2 to 10 mTorr. Subsequent annealing of the thin film fabricated at the Ar pressure of 10 mTorr at 150 °C leads to a 10-fold decrease in its SPM ratio from that in the as-deposited state. This decreased SPM ratio is, nevertheless, still higher than that of the thin film fabricated at the Ar pressure of 2 mTorr. These results indicate that the magnetic behaviors of amorphous Fe–Zr thin films are highly sensitive to the Ar pressure. Thus, it is crucial to take this parameter into account in the analysis of the magnetic behaviors of amorphous Fe–Zr thin films.

Evolution of Fe environments and phase composition during mechanical amorphization of Fe70Zr30 and Fe70Nb30 alloys

Amorphous Fe-Zr and Fe-Nb alloys with 70 at.% Fe have been prepared by ball milling a mixture of elemental powders. The combination of Mössbauer spectroscopy, X-ray diffraction, scanning electron microscopy and differential scanning calorimetry techniques supplies detailed information about the composition as well as microstructural parameters of remaining crystalline and amorphous phases developed during milling. Detailed analysis of the Fe environments allows us to distinguish Fe atoms in paramagnetic sites between those incorporated to crystalline Zr or Nb rich phases and those Fe atoms in amorphous phase.

Hyperfine interactions and some thermomagnetic properties of amorphous FeZr(Cr)NbBCu alloys

Abstract In this research, we studied the magnetic phase transition by Mössbauer spectroscopy and using vibrating sample magnetometer for amorphous Fe86-xZr7CrxNb2Cu1B4 (x = 0 or 6) alloys in the as-quenched state and after accumulative annealing in the temperature range 600-750 K. The Mössbauer investigations were carried out at room and nitrogen temperatures. The Mössbauer spectra of the investigated alloys at room temperature are characteristic of amorphous paramagnets and have a form of asymmetric doublets. However, at nitrogen temperature, the alloys behave like ferromagnetic amorphous materials. The two components are distinguished in the spectrum recorded at both room and nitrogen temperatures. The low field component in the distribution of hyperfine field induction shifts towards higher field with the annealing temperature. It is assumed that during annealing at higher temperature, due to diffusion processes, the grains of α-Fe are created in the area corresponding to this component. Both investigated alloys show the invar effect and the decrease of hyperfine field induction after annealing at 600 K for 10 min is observed. It is accompanied by the lowering of Curie temperature.

Large variation of magnetic properties of amorphous Fe\u2013Zr thin films with Ar pressure during sputtering

A large change is observed in the magnetic properties of amorphous Fe–Zr thin films sputtered at different Ar pressures. The change depends on the composition of the alloys and at compositions near 60 at.% Fe, for example, the magnetisation measured at 10 kOe increases 30-fold with an increase in the Ar pressure from 2 to 10 mTorr. The magnetic properties are well explained by a combination of two phenomena—superparamagnetism and spin glass behaviours—and the large change is partly related to the number density of a magnetically correlated region. Examinations of the microstructure by X-ray diffraction, transmission electron microscopy, and X-ray absorption fine structure spectroscopy reveal no appreciable difference in it as a function of the Ar pressure. This indicates that even a very slight change in the microstructure can greatly affect the magnetic properties of amorphous Fe–Zr thin films, thereby opening up the possibility of employing the magnetic properties of amorphous alloys for the characterisation of amorphous microstructures.

Magnetic structure and magnetic properties of nanocrystalline and amorphous Fe–Zr–N films

Data on the magnetic structure and magnetic properties of Fe–Zr–N films, which were prepared by reactive magnetron sputtering of a heated target and deposited on glass substrates, are reported. Depending on the Zr content (from 3 to 35at%), the film compositions are characterized by Zr-to-N (at%) ratio from 0.3 to 36.5. The magnetic properties (saturation magnetization Ms, coercive field Hc) and magnetic structure (effective local magnetic anisotropy field D1/2Ha, grain size 2Rc, effective anisotropy field of stochastic domain D1/2〈Ha〉, relative stochastic domain size RL/Rc) of the films are discussed in interrelation with their phase and structural states. The coercive field of the studied ferromagnetic nanocrystalline films was shown to obey the relationship Hc~(2Rc)6 and depends on not only the grain size but also the local magnetic anisotropy field D1/2Ha. As the grain size of ferromagnetic phase decreases, the contribution of the magnetoelastic component to the coercive field decreases. It was shown, by examples of weak ferromagnetic and superparamagnetic films with amorphous and mixed (amorphous+nanocrystalline) structures containing a nonferromagnetic phase, that the magnetic properties reflect the real structural and phase state of the films, which cannot be revealed by the X-ray diffraction analysis.

Magnetostatic spin wave in a very thin CoFeB film grown on an amorphous FeZr buffer layer

The transmission of a magnetostatic spin wave in a very thin CoFeB film (2.3 nm) grown on an amorphous paramagnetic FeZr layer was demonstrated for the first time by using an antenna method with coplanar waveguides. The attenuation length, determined by using the difference in intensities due to a change in the distance between the antennas, was estimated to be 0.7 µm. We discuss why we are able to observe spin-wave propagation in such a thin magnetic layer, taking the low damping constant (α = 0.0027) of the CoFeB films grown on the amorphous FeZr layer and the estimated large group velocity in the CoFeB films into account.

XPS and electron transport study of the paramagnetic dusting effect on MgO-based magnetic tunnel junctions

Amorphous FeZr was dusted in CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs), and the effects on tunnel phenomena were investigated. As the thickness of the FeZr layer between the CoFeB and the MgO layers increased, the resistance increased rapidly and the bias dependence became asymmetric while the tunneling magneto-resistance (TMR) decreased. The interface was investigated by using X-ray photoemission spectroscopy, and the change in the transport property due to dusting was explained.

Magnetic properties of amorphous Fe93Zr7 films: Effect of light ion implantation

The Curie temperature (Tc) of amorphous FeZr alloys can be greatly enhanced by doping with light elements. In this investigation, ion implantation is used to dope Fe93Zr7 thin films with H, He, B, C, and N. Extended X-ray absorption fine structure measurements confirm that the amorphous structure is preserved upon implantation for all samples, except for the N-implanted sample which is partially crystallized. The Curie temperature increases from 124 K for the pristine FeZr sample to about 400 K for the (FeZr)B0.11 sample. The increase of Tc is proportional to the increase in the average Fe-Fe distance, which allows us to conclude that the dominant cause of the Tc enhancement of amorphous Fe93Zr7 upon doping is a volume effect.

Perpendicular magnetization of CoFeB on top of an amorphous buffer layer

Perpendicular magnetic anisotropy was observed in sputtered FeZr/CoFeB/MgO multilayers. A thin paramagnetic amorphous FeZr layer was used as a buffer layer and perpendicular anisotropy was obtained by annealing the samples without an external magnetic field. The critical CoFeB thickness for perpendicular anisotropy was 1.8nm; the anisotropy changes from out-of-plane to in-plane as the CoFeB thickness increases beyond this point. Perpendicular anisotropy was also enhanced when a Ta layer was capped on top of the MgO layer. The amorphous buffer provided better perpendicular anisotropy than previously reported Ta buffer, and it may be applied to perpendicular magnetization MRAM devices where good uniformity of tunnel junctions is required.

Formation of a bcc (001)-textured CoFe layer by the insertion of an FeZr layer in multilayer-based stacks with perpendicular magnetic anisotropy

The effects of inserting an amorphous FeZr layer between the [Pt/Co] multilayer and the CoFeB/MgO layer in stacks possessing perpendicular magnetic anisotropy are examined. A 1-nm-thick FeZr layer is effective in forming a bcc (001)-textured CoFe layer during annealing by suppression of crystallization at the interface with the multilayer, which is terminated in a close-packed plane. Because FeZr is magnetic, it has an advantage over Ta, an alternative material used for the same purpose. Efficient magnetic coupling between the multilayer and CoFeB/MgO occurs even for large FeZr layer thicknesses, so the magnetic properties of the stack are only weakly affected.

Spin-filtering effect of thin Al2O3 barrier on tunneling magnetoresistance

Tunneling magnetoresistance (TMR) dependence on the Al2O3 barrier thickness was investigated for CoFe/Al2O3/CoFe magnetic tunnel junctions (MTJs). MTJs with very thin Al2O3 layers were grown by inserting an amorphous FeZr buffer layer whose role is only to reduce the roughness of bottom electrode. The TMR decreased as the thickness of the Al2O3 layer was reduced. The results are analyzed with the dependence of the spin-filtering effect on the Al2O3 thickness. It was found that a simple model of separating sp- and d-like electrons does not work, and it may suggest that the tunneling electrons are in rather hybridized state.

Relevance of Fe atomic volumes for the magnetic properties of Fe-rich metallic glasses

The atomic volume Va-Fe that can be assigned to Fe atoms in Fe–metalloid (Fe–MD) and Fe–early transition metal (Fe–TE) glasses was deduced in a previous paper (I. Bakonyi, Acta Materialia 53 (2005) 2509) from an analysis of available density data for such amorphous alloys. In the present paper, based on a similarity of the amorphous and face-centered cubic (fcc) structures, the distinctly different magnetic behaviors of these two families of amorphous alloys are discussed in terms of the relative position of Va-Fe and the critical volume Vfcc⁎-Fe≈11.7Å3/atom separating the so-called low-spin (LS) and high-spin (HS) state of fcc-Fe. For Fe–MD systems, Va-Fe is found to be definitely larger than Vfcc*-Fe whereas for Fe-TE systems Va-Fe is fairly close to Vfcc*-Fe. Since in topologically disordered alloys a distribution of atomic volumes is inherently present, in Fe–MD glasses the Fe atoms can be assumed to exhibit exclusively the HS state whereas in Fe–TE amorphous alloys a comparable fraction of Fe atoms can be either in the LS or the HS state. According to previous theoretical band structure calculations, an antiferromagnetic state can also be stable just around Vfcc*-Fe. The simultaneous presence of Fe atoms with such a rich variety of magnetic states due to the specific position of the average of the atomic volume distribution can well explain the complex magnetic behavior observed in Fe-rich Fe–TE metallic glasses such as, e.g., in amorphous Fe–Zr alloys around 90at% Fe.

Finite-size effects in amorphous Fe90Zr10/Al75Zr25multilayers

The thickness dependence of the magnetic properties of amorphous Fe90Zr10 layers has been explored using Fe90Zr10/Al75Zr25 multilayers. The Al75Zr25 layer thickness is kept at 40 \AA, while the thickness of the Fe90Zr10 layers is varied between 5 and 20 \AA. The thickness of the Al75Zr25 layers is sufficiently large to suppress any significant interlayer coupling. Both the Curie temperature and the spontaneous magnetization decrease non-linearly with decreasing thickness of the Fe90Zr10 layers. No ferromagnetic order is observed in the multilayer with 5 {\AA} Fe90Zr10 layers. The variation of the Curie temperature $T_c$ with the Fe90Zr10 layer thickness $t$ is fitted with a finite-size scaling formula $[1-\Tc(t)/\Tc(\infty)]=[(t-t')/t_0]^{-\lambda}$, yielding $\lambda=1.2$, and a critical thickness $t'=6.5$ \AA, below which the Curie temperature is zero.

Structure of Correlations in Fe99Zr10 Spin Glass

There are various representations for the long time evolution and the dynamics of spin glasses, but a coherent, overall accepted real space description remains lacking. Small-Angle Neutron Scattering measurements reveal the long range spin-spin correlations from which the correlation length as a function of the temperature, time or magnetic field can be deduced. The scattering of the amorphous Fe90Zr10 alloy during zero magnetic field cooling arises from long range correlations described by a Lorentzian function and scattering from spin clusters. From the temperature dependence of the correlation length two transitions are observed without, however, the correlation length to diverge. The application of magnetic field suppresses the transitions. The experimental findings are discussed in conjunction with different theoretical models.

Experimental realization of amorphous two-dimensionalXYmagnets

The temperature dependence of the magnetization of thin amorphous Fe(89)Zr(11)/Al(78)Zr(22) layerswas investigated. Dimensionality analysis of the ferromagnetic transition of 15 A thick layers yiel ...

Soft magnetic amorphous Fe–Zr–Si(Cu) boron-free alloys

Amorphous Fe 80Zr x Si 20− x− y Cu y boron-free alloys, in which boron was completely replaced by silicon as a glass forming element, have been prepared in the form of ribbons by using the melt quenching technique. X-ray diffraction and Mössbauer spectroscopy measurements revealed that the as-quenched ribbons with the compositions with x = 6–10 at.% and y = 0, 1 at.% are fully or predominantly amorphous. Differential scanning calorimetry (DSC) measurements allowed the estimation of crystallization temperatures of the amorphous alloys. Soft magnetic properties have been studied by the specialized rf-Mössbauer technique. Since the rf-collapse effect observed is very sensitive to the local anisotropy fields it was possible to evaluate the soft magnetic properties of the amorphous alloys studied. The rf-Mössbauer studies were accompanied by conventional measurements of hysteresis loops from which the magnetization and coercive fields were estimated. It was found that amorphous Fe–Zr–Si(Cu) alloys are magnetically very soft, comparable with those of the conventional amorphous B-containing Fe-based alloys.