Amorphous Gd-Fe Research Articles

Electric-Field-Enhanced Bulk Perpendicular Magnetic Anisotropy in GdFe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 Multiferroic Heterostructure.

Perpendicular magnetic anisotropy is important for increasing the information storage density in the perpendicular magnetic recording media, and for rare-earth-transition-metal alloys with bulk perpendicular magnetic anisotropy that generate great research interest due to their abundant interesting phenomena, such as fast domain wall motion and skyrmion. Here, we deposit amorphous GdFe ferrimagnetic films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 ferroelectric substrate and investigate the effect of electric-field-induced piezostrain on its bulk perpendicular magnetic anisotropy. The anomalous Hall effect and polar Kerr image measurements suggest an enhanced bulk perpendicular magnetic anisotropy by electric field, which originates from a positive magnetoelastic anisotropy due to the positive magnetostriction coefficient of the GdFe film and the electric-field-induced tensile strain along the z axis in Pb(Mg1/3Nb2/3)0.7Ti0.3O3 ferroelectric substrate. Our results enrich the electrical control of perpendicular magnetic anisotropy and are useful for designing spintronic devices based on perpendicular magnetic anisotropy.

Tunable magnetic domains and depth resolved microstructure in Gd-Fe thin films

This paper reports the tunability of magnetic domains and its correlation with depth-resolved microstructure in 100 nm thick Gd-Fe films after rapid thermal processing. The as-deposited films are amorphous in nature and display elongated periodic stripe domains, signifying the development of perpendicular magnetic anisotropy. Rapid thermal processing at 550oC for different time intervals viz. 5, 10, 15 and 20 min induces the crystallization of Fe over the amorphous Gd-Fe matrix and the presence of wider reaction zone has been evidenced at the film-substrate interface. While the magnetization measurements reveal a spin re-orientation along the plane of the film surface, the stripe domains are no longer observed for the processed films. 3D micromagnetic simulations have been performed to complement the experimental findings. The consideration of in-plane tilt of anisotropy axis along with anisotropy reduction successfully demonstrate the experimentally observed changes in magnetic properties and domain structure.

All-thermal switching of amorphous Gd-Fe alloys: Analysis of structural properties and magnetization dynamics

In recent years, there has been an intense interest in understanding the microscopic mechanism of thermally induced magnetization switching driven by a femtosecond laser pulse. Most of the effort has been dedicated to periodic crystalline structures while the amorphous counterparts have been less studied. By using a multiscale approach, i.e. first-principles density functional theory combined with atomistic spin dynamics, we report here on the very intricate structural and magnetic nature of amorphous Gd-Fe alloys for a wide range of Gd and Fe atomic concentrations at the nanoscale level. Both structural and dynamical properties of Gd-Fe alloys reported in this work are in good agreement with previous experiments. We calculated the dynamic behavior of homogeneous and inhomogeneous amorphous Gd-Fe alloys and their response under the influence of a femtosecond laser pulse. In the homogeneous sample, the Fe sublattice switches its magnetization before the Gd one. However, the temporal sequence of the switching of the two sublattices is reversed in the inhomogeneous sample. We propose a possible explanation based on a mechanism driven by a combination of the Dzyaloshiskii-Moriya interaction and exchange frustration, modeled by an antiferromagnetic second-neighbour exchange interaction between Gd atoms in the Gd-rich region. We also report on the influence of laser fluence and damping effects in the all-thermal switching.

Exchange coupling in the correlated electronic states of amorphous GdFe films

The bulk sensitivity of hard x-ray photoelectron spectroscopy in combination with circularly polarized radiation of the P09 beamline at PETRA III enables the investigation of the magnetic properties of capped films. We have determined the temperature dependence of the magnetic circular dichroism in the Fe 2$p$ and in the Gd 3$d$ states in amorphous GdFe films. The magnetic dichroism reflects the stronger temperature dependence of Gd moments compared to Fe moments in agreement with mean-field models. We resolved the exchange split Gd 3${d}_{5/2}$ substates and found a significant temperature dependence of the splitting which is attributed to a temperature dependent part of the exchange energy caused by Stoner-like itinerant states. A comparison of experimental and simulated x-ray photoemission spectra with corresponding data for x-ray absorption spectroscopy exciting the identical core holes clearly demonstrates that the core hole exchange interaction is the origin of the observed multiplet features for Gd.

X-ray resonant magnetic scattering study of magnetic stripe domains ina−GdFethin films

X-ray resonant magnetic scattering (XRMS) has been used to investigate the structure of magnetic stripe domain patterns in thin amorphous GdFe films. Under the influence of a perpendicular magnetic field, the scattered intensity displays a smooth transition from a structure factor of correlated stripes to the form factor of isolated domains. We derive a quite general expression that relates the total scattered intensity of XRMS to the absolute value of the magnetization. Furthermore, we compare our results for the domain period with domain theory. We obtain good agreement for prealigned stripes, but disorder tends to lead to an overestimation of the period measured with XRMS.

Probing the magnetic microstructure of an amorphous GdFe system with magnetic anomalous small angle x-ray scattering

The combination of x-ray magnetic circular dichroism (X-MCD) with anomalous small angle x-ray scattering (ASAXS) allows to determine size distributions and correlations lengths in the nanometer range of magnetic precipitates in granular systems. Results on an amorphous GdFe system with a pronounced perpendicular magnetic anisotropy are reported. Standard ASAXS measurements taken at the Fe K edge provide information on the electronic structure yielding a correlation maximum at 75 Å and an average particle radius of 6 Å. The magnetic scattering curves (MASAXS) were obtained at the corresponding Gd L3,2 edges. Their intensities can be explained by magnetic contributions to the anomalous scattering factors f′ and f″. A change of sign in the MASAXS is observed between profiles taken at the L3 and the L2 edge and with the change of circular polarization as expected from X-MCD.

Magnetic properties of crystalline and amorphous GdFe 2H x alloys prepared by hydrogenation

Magnetic properties of crystalline c-GdFe 2H 4.3 and hydrogen-induced amorphous a-GdFe 2H 3.3 which were prepared by hydrogenation of crystalline CdFe 2 with the C15 structure were investigated by magnetization measurements and 57Fe Mössbauer spectroscopy. The hydrogenation decreases the magnetic ordering temperature. The Curie temperatures are 360 K in c-GdFe 2H 4.3 and 469 K in GdFe 2H 3.3, which are noncollinear ferrimagnets with the compensation temperatures of 202 and 45 K, respectively. The Mössbauer spectra of c-GdFe 2H 4.3 at 297, 77.3 and 4.2 K consist of a sharp quadrupole doublet and a broadened Zeeman sextet, which indicates that a quarter of the Fe atoms do not carry an ordered magnetic moment even at 4.2 K. The spectra of a-GdFe 2H 3.3 show a broadened sextet with a distribution of hyperfine fields. The maximum of the distribution probabilities is located at 365 kOe at 4.2 K, a value which is larger than that of α-Fe.

The effects of high-energy milling on GdFe 2

With the aim of better understanding, the effects of severe milling on the magnetic and structural properties of crystalline compounds, samples of the intermetallic compound GdFe 2 were milled up to 276h under inert atmosphere and characterized by X-ray diffractometry (XRD) and Mössbauer spectroscopy (MS). On milling GdFe 2 a strong segregation of the elements Gd and Fe initially occurred, and the characteristic peaks of the initial compound GdFe 2 in the XRD pattern are absent after 1 h of milling. MS and XRD results also show that the milled samples contain a mixture of three main components: the segregated elements, the initial compound and an amorphous alloy, with relative proportions that vary with milling time. At the longer milling times the process induces a solid-state reaction between these components leading to the formation of an amorphous solid solution of Gd and Fe. In these cases the Mössbauer spectra taken at 300, 84 and 4.2 K were fitted with a combination of a set of peaks typical of metallic α-Fe and a continuous distribution of hyperfine magnetic fields that are ascribed to the amorphous Gd-Fe phase.

Circular magnetic x-ray dichroism in crystalline and amorphous GdFe2.

The spin-dependent absorption of circularly polarized x rays at the {ital K} edge of Fe and the {ital L}{sub 2} and {ital L}{sub 3} edges of Gd in amorphous and crystalline GdFe{sub 2} has been studied. Large differences in the magnitude of the dichroic signal are observed between the two samples. The application of recently derived sum rules indicates substantial quenching of the orbital moment in the amorphous sample. The results are compared to a theoretical spectrum for crystalline GdFe{sub 2}.

Study of Magnetic Properties on GdFe/Fe Multilayered Films

GdFe/Fe multilayers are “artificial ferrimagnets”, in which amorphous GdFe alloy layers and pure Fe layers are antiferromagnetically coupled to each other. A kind of spin flopping phenomenon is observed in their magnetization process. The magnetic structure change during the flopping, which is rather complicated compared with that of bulk ferrimagnets, was accounted for by a model calculation. The M - H curves were simulated by a “fan spin structure model”. Mössbauer spectroscopic analysis has been utilized to check the validity of the model structure. It has been demonstrated that the shapes of M - H curves are controlled to a certain extent by varying the thicknesses of Fe and GdFe layers and more extensively by inserting 3rd element layers at the interfaces of Fe and GdFe layers.

Effects of Film Thickness and Annealing Temperature on the Stress in Amorphous Gd-Fe Alloy Thin Films

ABSTRACTGd-Fe films were deposited by magnetron sputtering on glass substrates. The results shoved that the stress is compressive in most cases, and a larger compressive stress exists at the film-substrate interface. The stress is independent on the film thickness when the film thickness is greater than 0.20 μm. The stress becomes tensile only when the annealing temperature attains 400ºC. Therefore, the interfacial stress and the growth stress coexist in the Gd-Fe films, and the former will not be dominant when the film thickness is greater than 0. 2μm. The interfacial stress may originate from the inhomogeneous distribution of film composition at the interface, and the origin of growth stress can be explained by the atomic peening effect. The relation between the stress and the annealing temperature can be comprehended with the amorphous structure model.

Magnetic Properties of GdFe/Fe Multilayered Films

Spin-flopping phenomena in multilayer films consisting of two magnetic materials were investigated. In contrast to ordinary ferrimagnets, in which spin flopping occurs under very strong fields, multilayer films can be designed to exhibit spin flopping under rather weak fields. Samples were prepared by alternate deposition of Gd-rich amorphous GdFe alloy and pure Fe, and spin flopping processes were studied at room temperature. Since the magnetization of a pure Fe layer is larger than that of a GdFe layer, under weak magnetic fields the Fe layer magnetization is aligned in the direction of the external field, whereas that of the GdFe layer is antiparallel. At a certain critical field, the magnetization of the GdFe layer begins to turn in the direction of the external field. The field dependence of the magnetization is accounted for by assuming a twisted spin structure in the GdFe layer.

Stresses in Amorphous Gd-Fe Alloy Thin Films Deposited by Magnetron Sputtering

ABSTRACTAmorphous Gd-Fe alloy thin films were made by D.C. planar magnetron sputtering under various deposition conditions (e.g., film thickness, composition, working pressure of Ar, negative bias voltage and deposition rate). The stress, the film composition and the content of entrapped Ar in the films were measured respectively. The experimental results showed that in this case the working pressure of Ar and the negative bias voltage did not change the composition of the films, and the stresses were all compressive except for the films deposited in a very high working pressure of Ar. The origin of the compressive stress can be attributed to the atomic peening effect produced by fast neutral working gas atoms rebounded from the sputtering target. The magnitude of the compressive stress depends not only on the amount of Ar atoms incorporated in the films but also on the film microstructure such as the packing density.

ＧｄＦｅ／Ｆｅ人工格子の磁性

Spin flopping phenomena in multilayers consisting of two magnetic materials were investigated. In contrast to usual ferrimagnets where spin flopping occurs at a very high field, multilayers can be designed so as to exhibit the spin flopping in a rather low field. Samples were prepared by alternate deposition of Gd-rich amorphous GdFe alloy and pure Fe, and spin flopping processes were studied at room temperature. Since the magnetization of a pure Fe layer is larger than that of a GdFe layer, at low magnetic fields, the magnetization of the Fe layer is aligned to the direction of the external field whereas that of the GdFe layer is antiparallel. A certain critical field, the magnetization of the GdFe layer begins to turn to the direction of the external field. The field dependence of magnetization is accounted for by assuming a twisted spin structure in GdFe layer.

Hall effect in a RE-TM perpendicular magnetic anisotropy film under pulsed high magnetic fields

We measured the Hall loop of an amorphous GdFe film with perpendicular magnetic anistropy under a pulsed high magnetic field. We observed a very interesting behavior of the Hall loop which was considered to be related to a spin-flopping phenomenon.

Forced magnetostriction in amorphous Gd-Fe films

Composition and temperature dependence of forced magnetostriction have been measured for rf-sputtered Gd-Fe films using the cantilever capacitance method. Forced magnetostriction varies remarkably with film composition and temperature, and also depends on the substrate bias voltages applied during sputtering. It has been found that the change of forced magnetostriction coincides well with the change of the parameter δ, where δ is amount of fluctuation in the exchange constant between sublattice moment, and it has been evaluated by using Handrich’s modified molecular field theory. Therefore, we conclude that forced magnetostriction of sputtered Gd-Fe films is strongly related to δ.

Magneto-optic Kerr effect of amorphous Gd-Fe films

The magneto-optic polar Kerr spectra (λ = 400 to 700 nm ) have been measured at 4.2 K for amorphous Gd-Fe, Gd-Cu, Gd-Ni and Y-Fe films. The spectra of Gd-Fe films are compared with those of amorphous films with single magnetlc component. It has been found that Gd-Cu and Gd-Ni films have Kerr spectra very different from crystalline Gd : The Kerr rotation θ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</inf> is comparable to Gd at 400 nm while it becomes much smaller at 700 nm. The Kerr spectra of Gd-Fe films were found to agree qualitatively with the additive expression, θ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</inf> = K(Fe).4πMs(Fe) + K(Gd).4πMs(Gd), where K(Fe) and K(Gd) are estimated from single magnetic component films. The results suggest that Gd contributes to the Kerr rotation in the short wavelength range.

Forced Magnetostriction in Amorphous Gd-Fe Films

The relation between forced magnetostriction in amorphous Gd-Fe films and film composition was studied. It was discovered that the forced magnetostriction previously considered to be small enough to ignore is actually too large to ignore. The forced magnetostriction exhibits a significant dependence on film composition suggesting that it is strongly related to the Fe moment in the film. It was also confirmed that Gd-Fe film forced magnetostriction is dependent on temperature.

The Effects of Sm on Amorphous Gd-Fe Thin Films

Sm was added to GdFe films to make GdSmFe amorphous films and their magnetic characteristics were studied. It was found that GdSmFe films with quality equal to TbFe films could be produced. This indicates that GdSmFe could be viable as a magneto-optical medium.

非晶質Ｇｄ遷移金属薄膜の磁気光学効果及び磁性

Magneto-optic Kerr effect of amorphous (a-)GdFe films has been investigated by separating each magneto-optic contribution of Gd and Fe. Amorphous GdCu and YFe alloy films which consist of a single magnetic element have been prepared and their magnetization and polar Kerr rotation in the wavelength range of 400-700 nm have been measured at liq. N2 temperature. From the Kerr spectra of a-GdCu and a-YFe and their magnetization, the constant K(λ) defined by θK=K(λ), M(T) has been estimated. Using the K(λ) values we have separated each contribution of Gd and Fe to the Kerr rotation of a-GdFe. Comparing the Kerr spectrum of a-GdFe with that calculated from θK= KGd(λ) · MGd(T)+KFe(λ) · MFe(T), the Kerr spectrum of a-GdFe is fairly well explained by superposition of the contribution of Gd and Fe. It is concluded that the contribution of each sublattice is quite dependent on the photon energy in the range of 1.5 to 3 eV. Especially, the contribution of Gd becomes large with increasing photon energy and comparable to that of Fe at λ =400 nm.