FeTaN Thin Films Research Articles

First principles calculations of interfacial adhesion energy between Fe substrate and transition layer of films

Transition metal nitride films have high hardness and low wear rate, but the film substrate bonding strength between the film and the Fe substrate determines whether the film is useable. Adding transition layer materials is an effective way to improve the bonding strength of the membrane substrate. This article selects Ti, Zr, Hf, V, Cr, Ta, and TiN as transition layer materials, and uses first principles to calculate the interface bonding energies of ten interface models: Fe/TaN, Fe/Cr, Fe/V, Fe/Ti, Fe/Zr, Fe/Hf, Fe/Ta, Fe/TiN, Ti/TiN, and TiN/TaN. The model with higher bonding energy is selected to calculate the atomic population, electron gain and loss, and partial wave density of states of atoms, and further study the bonding situation at the interface. By comparing the bonding energy, the interfacial bonding energy between Fe and transition layer materials Ti, V, Cr, Ta, and TiN is higher than that of Fe and TaN films. And the interfacial binding energy of Fe/Ti, Ti/TiN and TiN/TaN are 0.3041eV/Å2, 0.4217eV/Å2 and 0.3687eV/Å2, respectively, which are higher than that of Fe and TaN film. Therefore, when preparing TaN thin films on Fe substrates, adding a double transition layer material Ti/TiN between the Fe substrate and TaN thin films, forming an interface model with a four layer structure of Fe/Ti/TiN/TaN, can optimize the bonding force between the substrate and the film to the greatest extent.

Angular dependence of dynamic magnetic properties and magnetization orientation distribution of thin films

The angular dependence of dynamic magnetic properties of FeTaN thin films fabricated by rf sputtering deposition technique onto various substrates was investigated in conjunction with static magnetic characteristics. Thin films grown onto rigid and thick substrates show a well-defined uniaxial anisotropy and strongly distinct permeability spectra measured at various orientations while those samples grown onto flexible and thin substrates exhibit a less well-defined uniaxial anisotropy and much less different permeability spectra. The resultant variation of the magnetization orientation distributions obtained by retrieving the magnetization values from the permeability curves for different substrates can be interpreted in terms of the magnetic anisotropy dispersion due to stress.

Magnetic anisotropy and resonance frequency of patterned soft magnetic strips

FeTaN thin films of 100nm with in-plane uniaxial anisotropy were fabricated by rf magnetron sputtering and patterned into strips with width varied from 30to500μm along both the easy and hard magnetization axes of the unpatterned films. The values of effective magnetic anisotropy of the patterned films increase as the strip widths decrease. The ferromagnetic resonance frequency showed a corresponding increment from 1.38to2.58GHz as the strip width varied. It indicates that this method is effective to tune the ferromagnetic resonance frequency of magnetic thin films. The resultant permeability spectra were understood according to the well-known Kittel formula where an averaged shape anisotropy arisen from the patterning was taken into account for the strips patterned along the easy axis. For the strips patterned along the hard axis, the increase in resonance frequency in narrower strips is attributed to the strengthened internal domain pinning effect predicted from the domain patterns numerically calculated.

Ferromagnetic resonance frequency tuning of FeTaN thin films by strips patterning with angular displacements

FeTaN thin films with uniaxial anisotropy were fabricated by sputtering and patterned into strips with width of 21 µm, separation gap of 10 µm and angular displacement of 0° to 90° from the magnetic easy axis of the unpatterned films. The effective magnetic anisotropy field was effectively modified in both value and direction dependent on the displacement angle. The unpatterned thin films had a maximum permeability of μ′∼700, μ″∼1000 and a ferromagnetic resonance frequency of ∼1.1 GHz. After patterning, the ferromagnetic resonance frequency was found to be ranging from 1 to 1.8 GHz as the angular displacement was varied, indicating that this method is a viable way of tuning the ferromagnetic resonance frequency. These results were well explained according to the well-known Kittel's formula assuming two fold anisotropies in the patterned films.

Thickness-dependent properties of FeTaN thin films deposited on flexible substrate

The FeTaN thin films were deposited on the flexible plastic substrates by rf magnetron sputtering. Good soft magnetic properties with coercivity <10Oe have been obtained in the films with thickness <250nm. Relatively high values of the complex permeability and ferromagnetic resonance frequency were obtained and they can be adjusted by changing the film thickness. However, compared to the films on the rigid substrate, a decrease of the permeability level and a shift of the resonance peak in the permeability spectra have been noticed for the films on the flexible substrate. The electric properties, including sheet resistance, resistivity, and magnetoresistance for the films with various thicknesses, have also been investigated.

Thickness and angle dependence of the coercivity on highly uniaxial anisotropy FeTaN thin films

A set of single-layer FeTaN thin films with thickness ranging from 30 to 720 nm has been fabricated on silicon substrate by magnetron sputtering. Effort is focused on the dependence of the coercivity on the film thickness and on the angle of the external magnetic field applied. The rotation model has been used to calculate the angle dependence of the coercivity. It agrees well with the experimental polar plot of the coercivity when suitable values of the magnetocrystalline constant ( K 1) and the magnetoelastic constant ( K S ) are chosen. The change in shape of the polar plot of the coercivity with the thickness is attributed to the competition between the magnetocrystalline and magnetoelastic energies. The effect of grain size and stress to the coercivity is also discussed.

Thickness dependence of the magnetic anisotropy and 90° switch of the easy axis in FeTaN thin films

The polycrystalline FeTaN thin films with the thickness range from 30 to 700 nm have been fabricated and their magnetic properties have been investigated. The results show that, with the increase of the thickness of the films, the polar plot of coercivity changes its shape, from the horizontal-ellipse-like, the circular to the vertical-ellipse-like, i.e. the in-plane easy axis undergoes a 90° switch. A model that considers the competition between magnetocrystalline anisotropy and magnetoelastic anisotropy induced by the stress as well as the distribution of the easy axis is proposed. Based on the model, the polar plots of coercivity are calculated and the results are well consistent with the experimental data. The torque experimental curves are also described well by the model.

Morphological Structure and Magnetic Properties of FeTaN Films

Nanocrystalline FeTaN thin films with a high Ta content were prepared in a reactive magnetron sputtering system. The as-sputtered films consist of the amorphous phase. The morphological structure and magnetic properties were investigated. Nanocrystalline alpha-Fe grains with the (110) plane parallel to the film surface crystallize from the amorphous phase after proper annealing. The film sputtered in low nitrogen partial pressure exhibits excellent soft magnetism because the alpha-Fe grains crystallized only with grain size less than the ferromagnetic exchange length. Nitrogen atoms play an important role in refining the alpha-Fe grains and inducing uniaxial anisotropy in the Fe-Ta-N films.

Microstructure, magnetic and nanomechanical properties of FeTaN filmsprepared by co-sputtering

FeTa and FeTaN thin films have been fabricated by sputter depositionfrom separate Fe and Ta magnetron sources. Microstructural investigationsrevealed that FeTa binary alloy films undergo a nanocrystalline to amorphoustransition at about 17 at% Ta. This transition is associated with rapidsimultaneous reductions in coercivity and saturation magnetization andincreases in hardness and resistance to plastic deformation. Below 17 at% Tathe films exhibit a single-phase bcc structure and their lattice spacingincreases linearly with Ta addition in agreement with Vegard's law, whichindicates the incorporation of Ta in substitutional sites. The grain size andcoercivity of the bcc binary films is seen to increase considerably withincreasing Ta content. The addition of nitrogen causes a decrease in grainsize, which is accompanied by a reduction in coercivity and an enhancement ofhardness.

Origin and thermal stability of HK in FeTaN thin films

In this study 2000 Å FeTaN thin films are annealed at 150 °C in both longitudinal and transverse magnetic fields. Both anneals result in a decrease in HK, which is shown to be a result of interstitial N, however, the transverse anneal results in a 90° rotation of HK and a 33% larger decrease in the magnitude of HK as compared to the longitudinal anneal. Subsequent transverse field anneals show that HK is completely reversible in relatively short times at any temperature above 75 °C. Our results are consistent with the diffusion of interstitial N being responsible for the rotatable behavior of HK in FeTaN.

Magnetostriction constants of [110] oriented epitaxially grown FeTaN thin films

The magnetostriction constants, /spl lambda//sub 100/ and /spl lambda//sub 111/, of FeTaN (10 wt% Ta) were determined in [110] oriented epitaxial thin films (/spl sim/1500 W) deposited by dc magnetron sputtering onto Cu[001] buffer layers (/spl sim/2000 /spl Aring/) which were grown on Si[001] single crystal substrates. The orientation relationship of the films was FeTaN[110]/spl par/Cu[001]/spl par/Si[001] with FeTaN<111>/spl par/Cu<110>/spl par/Si<100>, which was satisfied by four different, equally probable in-plane orientations of the crystallites. The magnetostriction measurement was carried out on a cantilever beam measurement system calibrated with [110] oriented epitaxial Fe films with the same morphology as the unknown films assuming the bulk values of /spl lambda//sub 100/, and /spl lambda//sub 111/. The magnetostriction of FeTaN films was measured as a function of angle in the sample plane and fitted with the calculated average of the four orientations. In conflict with theoretical predictions, it was found that /spl lambda//sub 100/ decreases and /spl lambda//sub 111/ increases as a function of lattice dilation which was taken to be proportional to the interstitial concentration. At larger normalized lattice dilation, /spl sim/2%, /spl lambda//sub 111/ changed sign from negative to positive. The calculated saturation magnetostriction, /spl lambda//sub s/, using these values of /spl lambda//sub 100/, and /spl lambda//sub 111/ agreed with published data on nanocrystalline samples of the same composition with no additional assumptions.

Magnetic and structural properties of epitaxially grown FeTaN thin films

Epitaxial FeTaN films (∼1500 Å) were grown as a function of nitrogen flow rate on epitaxial Cu(001) buffer layers (∼2000 Å) on Si(001) single crystal substrates to investigate the effect of Ta and nitrogen on the magnetocrystalline anisotropy and magnetostriction. Detailed structural investigation by transmission electron microscopy and x-ray diffraction showed that the FeTaN films were epitaxial with the Pitsch orientation relationship of FeTaN(110)∥Cu(001) and FeTaN〈111〉∥Cu〈110〉, which allows four different in-plane variants to coexist in the film. It was found that the saturation magnetization did not change with nitrogen addition (∼1600 emu/cc) up to 2% lattice dilation. The values of K1 and λ100 of Fe decreased slightly (20% and 10%, respectively), while λ111 increased with increasing nitrogen content and eventually changed sign at ∼2% normalized lattice dilation. These results qualitatively agree with our earlier findings on (001) oriented FeTaN epitaxial films on MgO single crystal substrates. Also, our calculated saturation magnetostriction for nanocrystalline samples agrees very well with published data on the same FeTaN composition. Based on Hoffmann’s ripple theory the ripple constant is calculated for nanocrystalline films using the Doyle–Finnegan model for the local average anisotropy and our measured single crystal constants. It was found that the effect of nitrogen on reducing the average anisotropy through the fundamental constants is not significant, and therefore the major factor in achieving a low ripple constant (i.e., soft magnetic properties) is the grain size, the number of grains across the thickness and the thin film stress.

Artificially controlled stress anisotropy and magnetic properties of FeTaN thin films

This article presents a new method of investigating internal stress effects on thin film magnetic properties, in this case magnetically soft FeTaN sputtered films. The FeTaN films were deposited on a series of oxidized silicon (111) substrates prestressed to different degrees. During sputtering all the deposition conditions were kept exactly the same for all the samples. However, anisotropic stresses with different amplitudes are systematically introduced into the films when the prestressed wafers were released. In this way, FeTaN films with compressive stress varying from 80 to 608 MPa are produced. We found that the saturation magnetostriction (λs), anisotropy field (Hk), initial permeability (μi) as well as easy axis orientation of FeTaN thin films are strongly affected by the induced stress anisotropy. A stress ratio concept is proposed as a measure of the degree of the stress anisotropy. Models for easy-hard axis switching induced by stress for magnetic films with positive magnetostriction are discussed.

Thermal stability of FeTaN as a function of N and Ta content

FeTaN thin films promise to be a good candidate for inductive head pole materials. FeTaN thin films which are nanocrystalline and possess the required magnetic properties in the as-deposited state are advantageous because they do not require a high temperature processing anneal. However, FeTaN films must possess sufficient thermal stability in order to maintain their magnetic properties while being processed into inductive heads. In this study we have undertaken systematic microstructural and magnetic measurements on nanocrystalline, single-layer FeTaN thin films as a function of N and Ta content and annealing temperature. The annealing temperatures used are less than 300/spl deg/C and are meant to simulate head processing conditions. The addition of Ta was found to enhance thermal stability. By stabilizing the microstructure, Ta also stabilizes magnetic properties such as coercivity and magnetostriction (structure determines properties). The optimum amount of Ta for thermal stability while maintaining good magnetic properties was 10 weight percent. In the highest N content Fe-10TaN thin films, soft magnetic properties were found to be controlled by the magnetic domain structures which are governed by magnetoelastic anisotropy. These films which exhibited a magnetoelastic anisotropy less than -2/spl times/10/sup 4/ ergs/cm/sup 3/ also exhibited stripe domains which resulted in relatively high coercivities.

Ferromagnetic resonance and eddy currents in high-permeable thin films

The effect of eddy currents and ferromagnetic resonance (FMR) on the frequency dependence of the permeability of FeTaN thin films is studied. An equation is given that describes the combination of these two effects. The agreement between the theoretical calculations and the experimental data is excellent. Already at 1 MHz the imaginary part of the permeability is significantly changed by FMR. Above 10 MHz the real part of the permeability is decreased by FMR. The combined effect is best observed in extremely high permeable, 1 μm thick films. A value for the ferromagnetic damping constant is obtained.

Effect of nitrogen interstitial in α-Fe crystalline on the magnetic soft properties of FeTaN thin films

The effect of nitrogen interstitial in α-Fe crystalline on the magnetic soft properties of Fe87.5Ta12.5Nx films has been investigated. The magnetic soft properties can be improved by carefully controlling the nitrogen flow ratio during sputtering and the postannealing to result in a film with fine grain size and low magnetostriction. Using x-ray diffraction technique, the nitrogen content in the α-Fe crystalline of FeTaN film can be estimated from the effect of lattice expansion of α-Fe crystalline due to nitrogen interstitial. It is found that the film with about 7.5 at. % N2 in α-Fe crystalline exhibits the best magnetic soft properties of Br=1.6 T, Hc=0.2 Oe and μi(1 MHz)=3400, respectively. X-ray diffraction analysis is found to provide a proper and an easy way to identify the suitable condition for growing excellent magnetic soft FeTaN thin films.

Magnetostriction and thin-film stress in high magnetization magnetically soft FeTaN thin films

Domain structures in thin-film heads can be significantly influenced by magnetoelastic anisotropy. In this study we have undertaken systematic measurements of magnetostriction and stress in as-deposited and annealed states in FeN and FeTaN single-layer thin films with varying nitrogen contents. Magnetostriction was positive for FeN films, increased with increasing nitrogen content, and shifted toward negative values after annealing. Stress in as-deposited FeN films was tensile and decreased (became more compressive) with increasing nitrogen content. Annealing the FeN films resulted in significant stress relief. By contrast, magnetostriction was found to be negative for simple FeTa (zero nitrogen) and increased linearly with increasing nitrogen content to positive values. The magnetostriction in FeTaN did not change significantly after annealing at 200 and 250 °C. FeTaN film stresses were compressive in the as-deposited state and increased in magnitude (became more compressive) with increasing nitrogen content. After annealing these stresses were relieved slightly. Ta has been found to be very effective in enhancing the thermal stability of the FeN films.

The Effect of Ta and N Content on Mechanical Properties of DC Magnetron Sputtered fen and Fetan thin films

AbstractThis paper reports nanoindentation studies of the effect of Ta and N content on the mechanical properties of magnetically soft high moment FeN and FeTaN thin films prepared by dc magnetron sputtering. The FeTaN films were deposited on oxidized silicon (100) substrates with a series of FeTa targets in which the Ta content varies from 0 to 25wt%. The hardness (H) and Young's modulus (E) were measured by the Nano Indenter at nine indenter penetration depths: 20, 30, 40, 50, 60, 80, 100, 120 and 200 nm. The inherent hardness values of these films (no substrate effect) can be determined at penetration depths ranging from 20 to 60 nm for the 500 nm thick film used in the study. It was found that for the films deposited from the pure Fe target when the nitrogen flow rate increases from 0 to about 0.5 sccm the hardness of the film increases. However, a decreasing trend in hardness of these films was observed on further increasing the nitrogen flow rate. On the other hand, for the films prepared from the targets with the Ta content in the range of 5–15wt%, the hardness increases whenever Ta and N contents increase. These effects are clearly illustrated by 3-D and contour hardness and Young's modulus maps in this paper.

Comparison of mechanical and tribological properties of permalloy and high moment FeTaN thin films for tape recording heads

This paper reports experimental results of a comparative study for mechanical and tribological properties of permalloy (NiFe) and magnetically soft high moment FeTaN sputtered thin films. It was observed that the hardness, elastic modulus and wear resistance of FeTaN films are all superior to those of NiFe permalloy films. AFM observations on unworn films and worn surfaces of a wear scar revealed that pit formation may contribute to wear damage mechanisms for low load abrasive wear.

Nanoindentation and tribological studies of magnetically soft high moment FeTaN thin films

The nanoindentation and tribological behavior of magnetically soft high moment FeTaN thin films have been investigated. It was observed that the hardness of FeTaN films increases when nitrogen is incorporated into the film and the wear resistance of these films against commercial magnetic tapes was increased by introducing a small amount of nitrogen but decreased with a further increase of nitrogen content. SEM observations on cross section of a wear scar revealed that there were debris particles (less than 0.5 /spl mu/m) on the worn surface.