Ar Chezan

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.

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.

Magnetization dynamics of soft nanocrystalline thin films with random magnetocrystalline anisotropy and induced uniaxial anisotropy

Results of frequency-dependent ferromagnetic resonance (FMR) measurements are presented for thin Fe-Zr-N nanocrystalline films with random magnetocrystal line anisotropy and induced uniaxial anisotropy. The study is done by changing the composition, the grain size and the magnitude of the induced anisotropy. We show that the magnetization dynamics is strongly influenced by the structural parameters of our samples. Although the frequency-dependent spectra can be analysed on the basis of the Landau-Lifshitz equation, an extra field H-shift has to be introduced in order to have agreement between the experiment and calculations. This extra field does not depend on the saturation magnetization and increases significantly when the grain size decreases from 10 to 2 nm. In addition, we observe a nonlinear decrease of the frequency linewidth with the applied dc field. After discussing various existing models we conclude that H-shift originates from variations in the magnitude of the magnetization, related with the nanocrystalline structure.

Soft magnetism in nitrided Fe93Ni4Cr3 and Fe94Ni4Ti2 cold-rolled alloys

The magnetic properties in relation with the structure of nitrided cold-rolled Fe93Ni4Cr3 and Fe94Ni4Ti2 were studied. Various low-temperature nitriding treatments were applied in order to obtain soft magnetic materials. We show that the magnetic anisotropy depends sensitively on the nitrogen content. The lowest value of the coercive force, H-C = 40 A/m was obtained for samples containing TiN precipitates. For the Cr contained samples, a concentration of 14% (FeNi)(4)N (gamma)-phase decreases H-C below values corresponding to the samples containing only CrN precipitates. We discuss the influence of the texture on the magnetic properties of samples containing only BCC alpha-phase, a mixture of alpha + gamma-phase, or samples which have been cycled through the epsilon-phase. Although grain refinement is observed after cycling and an almost random orientation of the grains is obtained, the magnetic properties do not improve. This is due to the fact the grain size is still too large to lead to averaging out of the magnetic anisotropy. Moreover, the stress/strain distribution developed during the treatments hampers domain wall motion and leads to an increased coercivity