D.O. Boerma

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.

Development of epitaxial nitride-based bilayers for magnetic tunnel junctions

This paper reports on the growth and properties of bilayer structures consisting of insulating epitaxial Cu/sub 3/N films grown on epitaxial ferromagnetic /spl gamma/-Fe/sub 4/N films. The interface between the layers is successfully probed with Mossbauer spectroscopy. In our fully epitaxial system, no intermixing occurs at the interface. Depending on the growth parameters (gas mixture, deposition temperature), the interface is also free of undesired nitride phases.

On the growth of magnetic Fe4N films

Magnetic epitaxy films of Fe4N have been grown by molecular beam epitaxial in a flow of atomic nitrogen from a radio-frequency plasma source. Various mixtures of nitrogen and hydrogen have been used in the source during evaporation of Fe-57 on a MgO(1 0 0) substrate. The admixture of hydrogen leads to an increase of the uptake of nitrogen by iron and it improves the crystalline properties of the films grown. It was found that the increased nitrogen uptake is due to a higher fraction of atomic N in the output of the source plus transport system. The sticking coefficient of N atoms to an iron and a Fe4N surface was found to be equal to unity under the conditions we used. The composition and the morphology of the films was studied with conversion electron Mossbauer spectroscopy, X-ray diffraction, RBS/channeling and atomic force microscopy measurements. The results obtained clarify in part the growth mechanism of the iron nitride layers and the influence of hydrogen

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.

Development of an all-nitride magnetic tunnel junction

We are developing an all-nitride magnetic tunnel junction. Here, we report on the growth and properties of gamma-Fe4N, alpha-Fe16N2 and Cu3N. Epitaxial gamma-Fe4N films were grown by molecular beam epitaxy of iron in the presence of atomic nitrogen from an RF atomic source. Layers of Cu3N were grown in a similar fashion. The alpha-Fe16N2 phase was synthesized by nitriding epitaxial iron layers. Up to now, Cu3N and alpha-Fe16N2 were not obtained as pure phases

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.

Thermal stability of electrodeposited soft-magnetic iron alloy layers

Summary form only given. Uniaxial in-plane anisotropy is introduced in soft magnetic layers made by electrodeposition. The anisotropy is caused by directional effects during production or subsequent annealing. A necessary condition for the usefulness of the layers is their thermal stability. In this work three electrodeposited alloys are investigated on the thermal stability of the uniaxial in-plane anisotropy.