Fe Trilayers Research Articles

Dynamic and static measurements on epitaxial Fe/Si/Fe

Strong antiferromagnetic interlayer exchange coupling across an insulating spacer is in increasing demand for high-density magnetic recording. We report here on the interlayer exchange coupling of epitaxial Fe(8 nm)/Si(t)/Fe(10 nm) trilayers as a function of Si thickness studied by ferromagnetic resonance (FMR), Brillouin light scattering, and magneto optic Kerr effect (MOKE) measurement techniques. A very strong antiferromagnetic (AFM) interlayer exchange coupling (>6 erg/cm2) was observed at a spacer Si thickness of 0.7 nm. The bilinear J1 and biquadratic J2 coupling constants were determined from (i) the fitting of the angular variation of the resonance field (Hres) in FMR experiments, (ii) the field variation of the frequencies of the Damon–Eshbach surface modes (both optic and acoustic) in BLS measurements, and (iii) the fitting of longitudinal MOKE hysteresis loops. We obtain a higher Hres along the easy axis than along the hard axis and the magnetizations of the two Fe films are canted. The eightfold-like symmetry of Hres as a function of the angle observed at room temperature is due to the competition between the Fe fourfold anisotropy and AFM interfacial coupling energy. This behavior vanishes at low temperatures due to a strong increase of AFM coupling (especially J2) in comparison to fourfold in-plane anisotropy. From the fitting of the temperature dependent FMR data, we obtain the temperature variation of the bilinear and biquadratic exchange coupling constants. We distinguish the existence of canted magnetization states at resonance by fitting the experimental Hres versus θH data to the model calculation.

Interlayer exchange coupling of epitaxial Fe/Al/Fe trilayer films: Dynamic and static measurements

This report deals with the interlayer exchange coupling of epitaxial Fe(3 nm)/Al(tAl=0.4–0.9 nm)/Fe(2 nm) trilayers studied by using ferromagnetic resonance (FMR), Brillouin light scattering (BLS) and magneto-optic Kerr effect (MOKE) measurement techniques. A very strong antiferromagnetic (AFM) interlayer exchange coupling (>3 erg/cm2) was observed at a spacer Al thickness of 0.7 nm. The bilinear (J1) and the biquadratic (J2) coupling constants were determined from (i) the fitting of angular variation (θH) of resonance field (Hres) from FMR, (ii) field variation of acoustic and optic surface mode frequencies from BLS and (iii) by fitting of longitudinal MOKE hysteresis loops. The samples with strong antiferromagnetic (AFM) coupling have a higher Hres along the easy axis than that along hard axis and their magnetizations are canted. The eightfold-like symmetry, of the acoustic Hres as a function of in-plane field angle at room temperature, is due to the strong competition between the fourfold anisotropy energy (HK) and the AFM interfacial coupling energy. This behavior vanished at low temperatures due to a strong increase of AFM coupling in comparison to HK. We distinguish the existence of canted magnetization states at resonance by fitting the experimental Hres(θH) data to the model calculation.

Relation betweenL2,3XMCD and the magnetic ground-state properties for the early3delement V

State-of-the-art x-ray magnetic circular dichroism measurements of V at the L 2 , 3 edges with an excellent signal-to-noise ratio are analyzed for a Fe 0 . 9 V 0 . 1 disordered alloy and a Fe/V 3 /Fe(110) trilayer which were prepared in UHV and measured in situ on a Cu(100) single crystal. The absorption fine structure and the magnetic dichroism are discussed in detail with the help of ab initio theory. Several approaches known from literature to obtain magnetic ground-state properties from experimental spectra are tested for their validity.

Magnetic properties, interlayer exchange coupling and electric transport in Fe/Cr/Fe trilayers

Abstract Based on the fully relativistic spin-polarized screened Korringa-Kohn-Rostoker method and the Kubo-Greenwood eauation as formulated for layered systems the interlayer exchange coupling (IEC) as well as the magneto-resistance (MR) for the current in-plane (CIP) geometry is calculated for Fe/Cr/ Fe trilayer systems. For the IEC not only short periods of 2 monolayers (ML) but also long periods of about 18 ML are found. For large Cr thicknesses the magnetic moments oscillate with a period of 8-9 ML for even numbers of Cr layers and 18 for odd. The calculated CIP MR and corresponding resistivities are in the range of available experimental data. It is found that the peaks in the CIP MR have little in common with the oscillation periods characterizing the IEC.

Magnetic properties, interlayer exchange coupling and electric transport in Fe/Cr/Fe trilayers

Abstract Based on the fully relativistic spin-polarized screened Korringa-Kohn-Rostoker method and the Kubo-Greenwood eauation as formulated for layered systems the interlayer exchange coupling (IEC) as well as the magneto-resistance (MR) for the current in-plane (CIP) geometry is calculated for Fe/Cr/ Fe trilayer systems. For the IEC not only short periods of 2 monolayers (ML) but also long periods of about 18 ML are found. For large Cr thicknesses the magnetic moments oscillate with a period of 8-9 ML for even numbers of Cr layers and 18 for odd. The calculated CIP MR and corresponding resistivities are in the range of available experimental data. It is found that the peaks in the CIP MR have little in common with the oscillation periods characterizing the IEC.

Metallic-type oscillatory interlayer exchange coupling across an epitaxial FeSi spacer.

We study interlayer exchange coupling in epitaxial Fe/Fe(0.56)Si(0.44)/Fe trilayers. Iron-silicide spacers with high structural and compositional homogeneity for thicknesses up to 34 A are grown by coevaporation from two electron-beam sources. The coupling strength oscillates with spacer thickness for temperatures from 20 to 300 K with two antiferromagnetic maxima at 12 and 26 A, and it clearly increases with decreasing temperature down to 80 K. We conclude that the coupling across ordered Fe(1-x)Si(x) ( x approximately 0.5) is described by the conventional theory of interlayer coupling across metallic spacers.

Oscillatory behaviour of magnetic and magneto–optical properties in Fe–Pt thin-film structures

Results of investigations into the influence of Pt on the magnetic and magneto–optical properties of Fe–Pt–Fe trilayers and the sandwich of wedge-shaped Fe and Pt layers are presented. The oscillatory behavior of the saturation field, H S, of the trilayers with changing the Pt-layer thickness, t Pt, was revealed. That was explained by the exchange coupling between the ferromagnetic layers through the nonmagnetic spacer. For the first time, oscillations of the transverse Kerr effect (TKE) with changing Pt-wedge thickness were discovered. The period of these oscillations was found to depend on the Fe-layer thickness and the photon energy of the incident light. TKE spectra of the examined samples were discovered to modify very strongly with increasing t Pt. The peculiarities of the magneto–optical properties of the Fe–Pt thin-film structures were explained by the concept of the spin-polarized quantum well states in the Pt-layer.

Tunneling spectroscopy in Fe-GaN-Fe trilayer structures grown by MBE using ECR microwave plasma nitrogen source

Epitaxy of Fe on GaAs by the MBE technique has a long tradition in magnetism research. This paper deals with the growth of epitaxial Fe–GaN–Fe trilayer structures whose intriguing magnetic properties were exploited for the evaluation of GaN as a spin-dependent tunneling barrier. The trilayers were grown on semi-insulating (0 0 1) GaAs using an ultra-high vacuum deposition chamber equipped with electron cyclotron resonance (ECR) microwave plasma nitrogen source.

Temperature dependence of the interfilm magnetic interaction in Fe/Cr/Fe trilayers

The behavior of the interfilm magnetic interaction in Fe(40 Å)/Cr( t Cr)/Fe(40 Å) trilayers ( t Cr=11, 13 and 15 Å), grown on MgO(1 0 0), is investigated theoretically and experimentally through ferromagnetic resonance. The experimental data show that for temperatures well below T c the temperature variation of the effective interlayer coupling arises mainly from the spin fluctuations of ferromagnetic films.

Growth and properties of Co/Al–O x/Ni(80)Fe(20) trilayers monitored in-situ during deposition process

The Co(25 nm)/Al( d Al)–O x /Ni 80Fe 20(25 nm), trilayers, with a Al thickness variation of 0.5 nm⩽ d Al⩽5 nm, were evaporated in ultra-high vacuum onto oxidised Si wafers. The simultaneous measurements of the magnetic hysteresis loops and thickness-dependent electric conductance were performed in-situ during deposition process. They were supplemented with surface topography and cross section images by atomic force microscopy and high-resolution transmission electron microscopy, respectively. We have shown that for an Al thickness of about 1.2 nm a transition from strongly ferromagnetically coupled Co and Ni 80Fe 20 characterised with single hysteresis loops to well separated magnetisation loops evident for weakly coupled layers occurs. The conductance measurements performed during deposition process as well as during 24 h oxidation process of the Al layer led us to the conclusion that independently on Al thickness nominally only 0.5 nm thick Al layer is oxidised. The influence of different buffer layers (Cu, Au) on magnetisation reversal characteristics is also shown.

Brillouin light scattering study of an exchange coupled asymmetric trilayer of Fe/Cr

The magnetic response of a (211) oriented asymmetric Fe trilayer [Fe(100 Å)/Cr(9 Å)/Fe(20 Å)/Cr(20 Å)/Fe(20 Å)], in which the thickness of the Cr spacer layers was chosen to produce ferromagnetic coupling (F) between the two thinner Fe layers and antiferromagnetic coupling (AF) between the thicker Fe layer and the adjacent thin one, has been investigated using magnetization and Brillouin light scattering (BLS) measurements. The coupling coefficients, extracted by fitting the BLS and magnetization measurements with a theory treating the static and dynamic response on an equal footing, produced consistent values of the magnetic parameters. Our results confirm that the theoretical model used in interpreting both static and dynamic properties is valid even in systems in which F and AF coupling of the layers are simultaneously present. The theoretical model has also been extended to include the field dependence of the intensity of the Brillouin peaks. The calculated intensities are compared with the BLS spectra at different applied fields.

Structure and Magnetic Properties of Fe-N Thin Films Grown by ECR Deposition

ABSTRACTThe growth of FexNy thin films on GaAs, In0.2Ga0.8As, and SiO2/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, y-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.

Structure And Magnetic Properties Of Fe-N Thin Films Grown By Ecr Deposition

ABSTRACTThe 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.

Biquadratic coupling dependence on spacer layer thickness for Fe/Cr/Fe

We report on exchange coupling properties in sputtered Fe(40 Å)/Cr( t)/Fe(40 Å) trilayers. By fitting Brillouin light scattering, ferromagnetic resonance and magneto-optical Kerr-effect data to theoretical expressions, the exchange coupling parameters J 1 and J 2 can be reliably extracted. We have found that the ratio J 1/ J 2 in the first negative peak is much bigger than recently reported. The FMR low-temperature measurements show a behavior which depends on the Cr layer thickness.

Biquadratic exchange coupling in sputtered Fe/Cr/Fe(100) sandwich structures

We have used magnetoresistance, magneto-optical Kerr effect, ferromagnetic resonance (FMR), and Brillouin light scattering to investigate interlayer exchange coupling in Fe(40 Å)/Cr(t)/Fe(40 Å) trilayers. At the right-hand side of the first antiferromagnetic peak (13 Å<t<16 Å), a common feature in both transport and magnetic measurements is the presence of sudden discontinuous jumps as the magnetic field is varied. By treating both transport and magnetic data on equal footing, we demonstrate that all measurements can be described by model calculations which elegantly take into account the same set of phenomenological parameters, characterizing the magnetic anisotropy, Zeeman, and bilinear and biquadratic exchange energies. Temperature-dependent FMR measurements reveal intriguing similarities between the bilinear and biquadratic coupling behaviors.

Exchange coupling in a Fe/Cu n/Fe bcc (001) trilayer

A first principles self-consistent Green's function technique for calculating the ground state electronic structure of interfaces has been applied to investigate the magnetic interaction in a bcc (001) Fe/Cu n /FE trilayer. The periodicity of the exchange coupling as well as the layer spin-resolved moments are found to be consistent with the coupling mechanism described by the RKKY theory.

Ferromagnetic resonance of evaporated Fe/Cu/Fe trilayers

A series of evaporated Fe(10 Å)/Cu(d)/Fe(30 Å) trilayers with Au buffer- and overlayer, where d = 10−68 Å, is investigated by means of ferromagnetic resonance at room temperature. Comparison of the resonance fields calculated on a two-magnetization model and the observed resonance fields yields exchange coupling J as a function of d. A singularity in J in the vicinity of d = 20 Å and a weak antiferromagnetic coupling for d > 40 Å are observed. The problem of the systematic deviations of the observed resonance fields from the calculated resonance fields is encountered. A gradual change in the anisotropy fields in Fe layers as d increases can explain the deviations. Another explanation based on effective magnetization is also presented by way of trial.

Ferromagnetic Resonance of Exchange-Coupled Fe/Au/Fe Trilayers

A series of evaporated Fe(30 A)/Au( d A)/Fe(10 A) trilayers with various Au interlayer thicknesses from 10 to 120 A is investigated by means of ferromagnetic resonance (FMR) technique at 300 K. Exchange coupling between Fe layers accounts for the change of FMR spectra. Comparison of the calculated and the observed resonance field values yields a coupling parameter J as a function of d . For d ≤18 A, the exchange coupling is strongly ferromagnetic. Antiferromagnetic coupling is realized for 75< d <85 A.