Layering and temperature-dependent magnetization and anisotropy of naturally produced Ni/NiO multilayers

Abstract

Ni/NiO multilayers were grown by magnetron sputtering at room temperature, with the aid of the natural oxidation procedure. That is, at the end of the deposition of each single Ni layer, air is let to flow into the vacuum chamber through a leak valve. Then, a very thin NiO layer ($1.2 nm) is formed. Simulated x-ray reflectivity patterns reveal that layering is excellent for individual Ni-layer thickness larger than 2.5 nm, which is attributed to the intercalation of amorphous NiO between the polycrystalline Ni layers. The magnetization of the films, measured at temperatures 5-300 K, has almost bulk-like value, whereas the films exhibit a trend to perpendicular magnetic anisotropy (PMA) with an unusual significant positive interface anisotropy contribution, which presents a weak temperature dependence. The power-law behavior of the multilayers indicates a non-negligible contribution of higher order anisotropies in the uniaxial anisotropy. Bloch-law fittings for the temperature dependence of the magnetization in the spin-wave regime show that the magnetization in the multilayers decreases faster as a function of temperature than the one of bulk Ni. Finally, when the individual Ni-layer thickness decreases below 2 nm, the multilayer stacking vanishes, resulting in a dramatic decrease of the interface magnetic anisotropy and consequently in a decrease of the perpendicular magnetic anisotropy. V

Magnetic Aspects and Large Exchange Bias of Ni0.9Co0.1/NiCoO Multilayers

“…A detailed XRR study has revealed that the thickness of the oxide layer is almost constant and reproducible [27]. The multilayers are structurally and magnetically repeatable.…”

“…Figures 3a, 4a and 5a show the magnetic hysteresis loops recorded by MOKE for three NiCo/NiCoO multilayers measured in the longitudinal (polar) geometry where the external magnetic field is applied parallel (perpendicular) to the film plane at R.T. The calibration of the Y-axis of MOKE loops in magnetization units was performed by taking 90% of the contribution of the magnetization of Ni magnetization from a Ni/NiO multilayer with the same individual layer thickness determined by SQUID [27], and adding 10% of the magnetization of bulk Co. One NiCo/NiCoO multilayer was measured by SQUID and the experimental result for the magnetization compared within 5% to our calculation approach verifying the validity of it. The easy magnetization axis for all samples is parallel to the film plane.…”

“…By following an alternative procedure, one may fabricate metal/metal oxide multilayer films, namely Ni/NiO [25][26][27][28] and Co/CoO [29], using only one sputtering head. The method uses natural oxidization, which results in an ultrathin oxide layer of constant thickness (of about 1.4 ± 0.2 nm) throughout the whole multilayer film.…”

Resonant x-ray diffraction revealing chemical disorder in sputtered L10FeNi on Si(0 0 1)

“…To protect the films from oxidation a cap layer of nominally 25Å Ni was deposited. Part of this Ni was expected to transform into a passivating NiO layer of about 15Å when subjected to air [25].…”

Strain engineering for controlled growth of thin-film FeNi L10

“…For the FeNi layer, a deposition rate of 0.136Å s −1 (or 0.076 ML s −1 ) was used for each element. To protect the films from oxidation a 20Å Ni cap layer was deposited which transformed into a passivating NiO layer of about 15Å after being exposed to air [25]. Using the same growth conditions, an additional control sample was grown in which the Fe and Ni were co-deposited to produce a film of similar thickness but in the chemically disordered A1 phase.…”