C.B. Craus

Stripe domains in Fe-Zr-N nanocrystalline films

We report on the transition between a magnetic stripe domain structure and in-plane orientation of the spins, as a function of nitrogen content, for 500nm thick Fe-Zr-N films prepared by DC reactive sputtering on glass substrates. The saturation field decreases and the saturation magnetization increases with decreasing nitrogen content. For 4at% N, the magnetic behavior of the films becomes specific for a soft magnetic material. The magnetic spin distribution was investigated by transmission Mossbauer spectroscopy (TMS) to probe the entire sample and Magnetic Force Microscopy to image the surface.

Structure and Soft Magnetic Properties of Fe—Zr—N Films

Soft magnetic films with high saturation magnetization and controllable uniaxial anisotropy are required for future high frequency applications. However, the origin and magnitude of the induced magnetic anisotropy are still a contradictory issue. In this paper we show the influence of the structure and composition of sputtered Fe-Zr-N films upon the coercivity and the induced uniaxial magnetic anisotropy. We have found that the increase of the nitrogen content of the sputtered films leads to a reduction of the grain size and a strong increase of the uniaxial anisotropy. The value of 20 Oe for the anisotropy field combined with a saturation magnetization of 20 kG found in a film with average grain size as low as 10 nm gives a ferromagnetic resonance frequency of 1.8 GHz and a roll-off frequency of 1.2 GHz. Such a film is a promising candidate to be used as an ultra-high frequency inductor.

Controlling the induced anisotropy in soft magnetic films for high frequency applications

Summary form only given. Soft magnetic materials with controllable uniaxial anisotropy are required for future ultrahigh frequency applications. Nowadays, the attention is focused on FeXN (X = Ta, Zr, Al). systems due to their high saturation magnetisation, excellent magnetic softness and good corrosion resistance. The films can be obtained in an as-deposited nanocrystalline state by sputtering Fe rich alloys in a reactive atmosphere (Ar + N/sub 2/). Such materials can be magnetically soft when the grain size becomes smaller than the ferromagnetic exchange length (as explained by the random anisotropy model). The anisotropy is created by a bias magnetic field applied during deposition or during a subsequent annealing. One limiting factor restricting the frequency range of applications is the natural ferromagnetic resonance. In order to push this limit in the GHz range, films with a uniaxial anisotropy field in excess of 20 Oe are desired. We have obtained films with excellent soft magnetic properties and controllable in plane uniaxial magnetic anisotropy by depositing Fe N films at different substrate temperatures. The induced in-plane anisotropy increases with increasing nitrogen content. Increasing the Zr/Fe ratio from 1/99 to 3/97 has little influence on the induced anisotropy.

Microstructure of nanocrystalline FeZr(N)-films and their soft magnetic properties

Abstract The microstructure of nanocrystalline FeZr(N) films, deposited by DC sputtering in a Ar+N 2 atmosphere was studied in correlation with their soft magnetic properties. The micromagnetic properties of the films were investigated using the Fresnel mode of Lorentz microscopy.

TEM study of Ti-N and Cr-N precipitate formation in iron alloys

The formation of precipitates of Ti and Cr nitrides in cold-rolled Fe + Ni(4at%) Ti(2at%) and Fe + Ni(4at%) + Cr(3at%) after a pre-nitriding step was investigated by Mossbauer spectroscopy (MS) and transmission electron microscopy (TEM). From MS data we conclude that initially most of the Ti and Cr were atomically dispersed. Using TEM and high-resolution TEM (HRTEM), we found that the Baker-Nutting (B-N) orientation relationship (OR) holds for platelets one to two interatomic distances thick, producing streaking around the (200) reflections, while for thicker pre- cipitates the Nishiyama-Wasserman (N-W) OR is more favorable. We also observed a transient phase, Cr2N, the formation of which was possible due to the relatively low nitriding temperature, a low nitriding potential, and the presence of Cr inclusions of relatively large initial size.

The influence of the surface topography on the magnetization dynamics in soft magnetic thin films

In this work we study the influence of surface roughness on the magnetization dynamics of soft magnetic nanocrystalline Fe–Zr–N thin films deposited (under identical conditions) onto a Si oxide, a thin polymer layer, and a thin Cu layer. The substrate temperature during deposition was approximately −25°C ensuring a nanocrystalline state. The demagnetizing factors due to sample roughness were calculated based on atomic force microscopy (AFM) analysis of the surface topography. A clear correlation between sample roughness and the width of the high-frequency response is observed. The local random demagnetizing field created by the nanocrystalline structure and the surface topography is responsible for the positive shift of the ferromagnetic resonance frequency. In addition, a pronounced effect of line broadening is induced by the surface topography at large wavelengths. Finally, we show a good agreement between the values of the average demagnetizing field 4πNMS as calculated from the AFM scans, and the valu...

A read and write element for magnetic probe recording

We present our results on the development of magnetic sensors for application in magnetic probe recording. Successful writing experiments on a magnetic medium with perpendicular anisotropy show that magnetic domains of 130 nm can be reversed in a heat-assisted process. For reading purposes we propose a magnetoresistive sensor. The optimization of the shape of the sensor was performed using micromagnetic simulations with the requirement that the sensor has to be capable of both read and write operations. At this stage, the experimental realization of the sensor was carried out at a wafer-base level. The fabrication technique consists of a combination of optical lithography and focused ion beam etching.

Relation between observed micromagnetic ripple and FMR width in ultrasoft magnetic films

Summary form only given. It was demonstrated that nanocrystalline FeXN films (X is an alloying element), obtained by sputtering or electrodeposition, have excellent ultra-soft magnetic properties with a saturation magnetization up to M/spl ap/2.0 T, a high magnetic susceptibility and a frequency range above 1 GHz. Here we report on a correlation between the microstructure, the micromagnetic ripples, and high frequency magnetism in the sputter-deposited FeZrN-films. The range of operating frequencies for the films is limited by the frequency of the ferromagnetic resonance (FMR) and by the width of FMR. Besides contributions to the FMR width due to dissipation sources, which are characteristic for crystalline and polycrystalline ferromagnetics, in nanocrystalline films there exists an additional contribution due to the local variation of the magnetic uniaxial anisotropy. Notwithstanding its importance, so far only a very few studies have been reported in the literature.

Evolution of nanaostructure of FeNi(Ti/Cr)N alloy during phase cycling

A possibility to manipulate the microstructure of cold rolled (down to less than 1% of the initial thickness) Fe94Ni4Ti2 and Fe93 Ni4 Cr3 foils via inter-phase cycling by nitriding and de-nitriding is investigated. The grains in the as-rolled material had a dominating (001)[110] texture and contained a complicated internal nanostructure due to a dislocation network. The interphase cycling α↔γ’-Fe4N and α↔ε-FexN (x~3) was investigated as a tool to change or destroy the texture. We observed that the α↔γ’-Fe4N phase transformations weaken but do not erase the texture. A stronger reduction of the texture was obtained in the α↔ε-cycling, where grains with a new orientation appear in XRD scans. During the α→γ’ phase transformation a lamella structure is formed which is coarsening with the number of cycles. It was found that the rates of the α↔γ’ and α↔ε interphase transitions were slowing down with the number of cycles. The observation is explained by an increase of kinetic barriers while removing/transforming the rolling-induced defects during the cycling.

On the GHz frequency response in nanocrystalline FeXN ultra-soft magnetic films

The periodicity and angular spread of the in-plane magnetization for ultrasoft nanocrystalline FeZrN films were estimated from an analysis of the ripple structure, observed in Lorentz transmission electron microscopy (LTEM) images. The influence of the micromagnetic ripple on the ferromagnetic resonance (FMR) width is analyzed using an approach based on the Landau-Lifshitz equation. A strong dependence of the resonance width on the magnetic moment dispersion is predicted. To a large extent this particular aspect explains the high frequency response in some of our films.