Fe Multilayer Films Research Articles

Microstructure and tribological behaviors of magnetron sputtered WS2/Fe/a-C/Fe multilayer films with various deposition temperatures

WS2/Fe/a-C/Fe multilayer films were prepared by using magnetron sputtering technique under various deposition temperatures. The composition, microstructure, mechanical and tribological properties of the films were characterized by energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), nano-indenter, scratch tester, film stress tester and ball-on-disk tribometer. With increasing deposition temperature, the film exhibits a morphology change from block-like to featureless, accompanied by a microstructural densification effect, its S/W ratio decreases from 1.14 to 1.04, and the hardness and adhesion are gradually enhanced. The films with deposition temperature ≥150 °C present better tribological performance than WS2/a-C multilayer film in vacuum and humid air. The film deposited at 300 °C achieves the highest hardness (9.0 GPa), a good adhesion (25.6 N), and the best tribological performance with a steady-state friction coefficient of 0.212 and wear rate of 7.07 × 10−15m3N−1m−1 in humid air, and steady-state friction coefficient of 0.165 and wear rate of 3.09 × 10−15m3N−1m−1 in vacuum.

Large Improvement of Coercivity in Sm-(Co,Cu)/Fe Films by Cu Addition

The magnetic properties and microstructure of Sm-(Co,Cu)/Fe films were investigated systematically. The addition of Cu is helpful for keeping a better multilayer structure due to the reduction of the crystallization temperature of the hard phase. With lowering the temperature, the coercivity of the Sm-(Co,Cu)/Fe films increases rapidly with a linear relationship. The Cu addition significantly improves the coercivities of the Sm-(Co,Cu)/Fe multilayer films, especially at the low temperatures. Adding the Cu as well as lowering the temperature cause a large inhomogeneity in the hard phase, and therefore a high pinning coercivity.

Sequential disordering during ion-induced amorphization in the Mo–Fe multilayered films

Amorphous alloys were formed within an extended broad composition range from 26 to 67 at.% of Mo by room temperature 200 keV xenon ion mixing of multilayered films in the Mo–Fe system with a small negative heat of formation of −3 kJ/mol, provided the multilayered films were properly designed to include sufficient fraction of interfacial atoms, thus possessing enough excess interfacial free energy. Moreover, a sequential disordering of Mo and Fe lattices was observed, for the first time, in the process of ion-induced amorphization in the Fe–Mo multilayered films. The sequential behavior can be attributed to the fact that Fe acted as a fast diffuser into Mo lattice, leading to an earlier disordering of the Mo crystalline structure and might be also associated with a difference in Debye temperature of the two metals.

Magnetostrictive effects in Cu/Co/Cu/Fe spin valve structures

We have investigated the magnetoelastic response of a series of Cu/Co/Cu/Fe multilayer films to applied stress by observing changes in the spin-valve magnetoresistance. The films were prepared by dc magnetron sputtering onto glass or polyimide substrates with individual layer thicknesses ranging from 35 to 50 Å. The typical magnetoresistance without external stress is about 1.2%. The strain induced by the applied stress varies from + 1600 (tension) to −1300 (compression) parts per million. We observed a decrease (increase) of coercivity with compressive (tensile) strain for both Fe and Co. This indicates that in the film plane, Fe and Co films have the same positive sign of magnetostriction. The observed coercivity change is about ±10 Oe for the maximum applied strain in both cases. The resulting maximum change in Δ R/R with a 1% strain is about −0.018 (+0.012) at the coercive field of Fe (Co).

Soft magnetic properties of Fe multilayered films with amorphous intermediate layers

Amorphous intermediate layers are studied to improve soft magnetic properties of Fe-based multilayers, since the interfacial stresses between layers are assumed to be low. Fe multilayers with crystalline intermediate layers (e.g., Ni-Fe alloy) required heat treatment to release interfacial stress to achieve soft magnetic properties. Multilayers Fe/B4C, Fe/SiC, and Fe/C (B4C, SiC, and C layers are amorphous when formed by ion beam sputtering) show relative permeabilities over 2000 and coercivities below 56 A/m (=0.7 Oe), even without heat treatment. In particular, Fe/B4C multilayers with B4C thicknesses over 0.5 nm show clear periodic structures, even smaller crystallite sizes, and relative permeabilities above 3000, while the films have saturation magnetic flux densities above 1.8 T.

Ｆｅ／ＦｅｘＮ積層膜の軟磁気特性に物ぼすＦｅｘＮ層の影響

Fe multilayered films with FexN intermediate layers of various structures (Fe + Fe4N, e + Fe4N, e and Fe2N) are prepared by reactive sputtering under various nitrogen partial pressure conditions. Effects of FexN intermediate layer on coercivity (Hc), saturation magnetization (Bs) and structure of Fe/FexN multilayered films are investigated. Fe/FexN multilayered films with intermediate layer prepared under conditions in which Fe2N single layer is obtained have a low Hc of less than 1 Oe. In these multilayered films, we observe that columnar growth of Fe layer is interrupted, grain size decreases below 100A and lattice spacing of α-Fe (110) plane increases. Low Hc of Fe/FexN multilayered films is thought to be caused by these results.

Changes in soft magnetic properties of Fe multilayered films due to lattice mismatches between Fe and intermediate layers

Fe multilayered films with various intermediate layers are formed. Their magnetic properties and film structures are examined to understand the mechanism originating soft magnetic properties. The soft magnetic properties change with the lattice mismatches between Fe and intermediate layers, showing low coercive force and high relative permeability at lattice mismatches from 0.4 to 1.2%. It is thought that the lattice mismatches above 0.4% decrease Fe crystallite size and improve soft magnetic properties. Although Fe crystallite size is small at the lattice mismatches above 1.2%, the soft magnetic properties are poor. This is because the large lattice mismatch increases internal stress and magnetic anisotropy energy. This report indicates that the good soft magnetic properties are obtained when both Fe crystallite size and internal stress are small.

Soft Magnetic Properties and Magnetic Anisotropy Dispersions of Fe–Ni/Ni–Fe Multilayered Films

Fe–2 at.%Ni/Ni–20 at.%Fe multilayered films are formed by the ion beam sputtering method. Their magnetic properties and magnetic anisotropy dispersions are examined. The Fe–Ni/Ni–Fe multilayered film of a 25 nm period displays a relative permeability of 1300 and a saturation magnetic flux density of 1.9 T. As the period of Fe–Ni/Ni–Fe multilayered films is reduced, the Fe–Ni crystallite size and the magnetic anisotropy dispersion become smaller, resulting in good soft magnetic properties.

Magnetic Properties and Magnetic Anisotropy Dispersion of Fe/Ni–Fe Multilayered Films

Fe/Ni–Fe multilayered films are formed by the ion beam sputtering method. Their magnetic properties and film structures are examined. As the period of the Fe/Ni–Fe multilayered films is reduced, the Fe crystallite diameter and the magnetic anisotropy dispersion become small and the soft magnetic properties are improved. The Fe/Ni–Fe multilayered film, whose period is 25 nm, displays a coercive force of 90 A/m, a relative permeability of 1900, a saturation magnetic flux density of 1.9 T, and a magnetostriction constant of 8×10-7. It is thought that the reduction of magnetic anisotropy dispersion improves the soft magnetic properties of Fe/Ni–Fe multilayered films.

Magnetic Properties of Composition Modulated Amorphous Zr¿Fe/Tb¿Fe Multilayered Films Prepared by RF Sputtering Method

The changes in structure and saturation magnetization (4πM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) due to composition modulation period (D), Curie temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ), perpendicular magnetic anisotropy (K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> ), and polar Kerr rotation in composition modulated multilayered films with amorphous Zr-Fe films and amorphous Tb-Fe films superimposed were studied. It was found that as D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , the composition modulation period calculated from the first X-ray diffraction peak, gets thinner, 4πM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> increases. This can be explained by the fact that magnetization of Fe within the Zr-Fe film is induced by the Tb-Fe film.