E. Klokholm

The measurement of magnetostriction in ferromagnetic thin films

The application of a magnetic field parallel to a ferromagnetic film deposited on one side of a cantilevered substrate causes a small deflection of the free end. This deflection can be measured and the magnetostriction determined since the magnetostriction is proportional to the deflection. An instrument has been devised which can measure the deflection as a function of the applied field. This is accomplished as follows: the cantilevered substrate with the film on the upper side forms one plate of a capacitor which is part of the tuning capacitance of an oscillator operating at l0 MHz. The deflection of the free end causes a change in frequency of about 10 to 100 Hz. which is easily measured. The sign of the magnetostriction is immediately discernible from the increase or decrease in oscillator frequency. The instrument is calibrated by hanging a known weight from the free end of the substrate. Magnetostriction constants as small as 3 \times 10^{-7} and as large as 40 \times 10^{-6} have been measured.

Magnetic properties and structure of cobalt-platinum thin films

The magnetic properties of RF sputtered Co-Pt alloy thin films were studied as a function of Pt content from 0 to 80 at%. At room temperature, ferromagnetic films were obtained in the range 0-32 and 40-80 at% Pt. For Pt contents between 32 and 40 at%, discontinuities in the magnetization, magnetostriction, and coercivity versus Pt content were observed; however no discontinuity was observed in the resistivity. The structure of films containing about 25 at% Pt is a mixture of hexagonal and face-centered cubic (FCC) phases. At this composition the magnetostriction is small, but coercivities are large-700 to 2000 Oe-and dependent upon film thickness. The coercivities of these films do not change with heat treatment up to temperatures of 600°C but decrease markedly at 700°C. The properties of equiatomic Co-Pt film s are similar to those of bulk alloys. In particular the large coercivity observed in films after heal treatment at 500° to 700°C is due to the formation of an ordered tetragonal phase within the face-centered cubic matrix. The structure of films of about 75 at% Pt is initially a disordered face-centered cubic phase and with heat treatment beginning at 500°C an ordered face-centered cubic phase forms. The coercivity of these films (∼200 Oe) does not change with annealing at 500°C. It decreases slightly upon further annealing at 600°C to 700°C. Electron microscope observations were used to correlate the magnetic properties with film structure.

The saturation magnetostriction of permalloy films

The saturation magnetostriction of permalloy films has been measured as a function of film composition. In general, the data obtained agrees with the published values for bulk polycrystalline permalloy. It has further been established that the composition for zero magnetostriction is at about 81.5 (wt.)% Ni. The exact composition for 0 magnetostriction is difficult to attain and for most films deposited under practical conditions the magnetostriction is small but slightly negative or positive. Various elements such as Cr, Rh, Ir and Ti have been added to permalloy films to enhance their corrosion resistance. The saturation magnetostriction of these films has been measured as a function of the amount of dilutent. All of the dilutents cause positive contributions to the saturation magnetostriction of permalloy films; Ir has the largest effect on λ, with the other elements Ti, Cr and Rh the effect on λ is less than Ir and decreases in that order.

Magnetic and structural characterization of sputtered FeN multilayer films

The magnetic and structural properties of ferromagnetic FeN thin films, FeN/FeN (ferromagnetic/paramagnetic), and FeN/SiO2 multilayers deposited in a rotational dc magnetron sputter system were investigated. Monolithic films containing ≂2 at. % N2 had 4πMs values ≂25 kG. The Fe16N2 phase has been identified by electron microdiffraction in these films. Saturation magnetostriction (λs) has been related to N2 content and can be varied from −3×10−6 to 5×10−6 in a range of compositions where 4πMs is ≳22 kG. Lamination reduced easy and hard axis coercivity to <1 Oe and produced single domain configurations in yoke‐shaped structures. Lorentz microscopy indicated that the ferromagnetic FeN layers in the FeN/FeN films were exchanged coupled while those in the FeN/SiO2 films were magnetostatically coupled.

Magnetostress Effects in Evaporated Ni Films

The residual stress in 1000‐A‐evaporated Ni films has been measured as a function of substrate temperature Ts. For Ts < 100°C, the stress is tensile and decreases with increasing Ts; at about 100°C, the tensile stress changes to compressive stress. As Ts increases beyond 100°C, the stress becomes increasingly compressive. A maximum in the compressive stress is observed at about 150°C, and then the stress decreases. Planar hysteresis loops obtained from a vibrating sample magnetometer show severely sheared loops for specimens under tensile stress; for specimens in compression the hysteresis loops are almost square. It has also been observed that the saturation magnetic moment of the films depends on the vacuum during deposition. Films deposited at a pressure of 10−7 Torr have larger moments than those prepared at 10−5−10−6 Torr. Although the magnetic moment depends on the degree of vacuum, the stress does not. Magnetic resonance and torque measurements show that the resonance field for the uniform mode, an...

Magnetic, transport, and structural properties of iron-platinum thin films

The magnetic, transport, and structural properties of RF sputtered Fe-Pt thin films were studied as a function of Pt content from 0 to 75 at.%. Polycrystalline ferromagnetic films were obtained in the range studied. The properties of the films are very similar to those obtained for bulk alloys. A body-centered-cubic phase is obtained for as-deposited films with less than 25 at.% Pt, and a face-centered-cubic structure is obtained for films with more than 25 at.% Pt. By annealing equiatomic Fe-Pt films, very large coercivities (about 10 kOersteds) can be obtained depending on the thickness, duration and temperature of annealing. The magnetization of Fe-Pt films is sufficiently large such that a moment of approximately 0.4 Bohr magneton must be associated with the Pt if Fe remains at 2.2 Bohr magneton per atom. The magnetostriction, Hall effect, and anisotropic magnetoresistance are all large near the equiatomic range of compositions.

Galvanomagnetic properties of transition metal-boron films

The Hall effect and the anisotropic magnetoresistance have been studied in Fe-B, Co-B and Co-Ni-B films. These are sputtered films with boron content from 5 to 37% and are only amorphous when B is above 15%. In all cases the alloys are ferromagnetic at room temperature. Amorphous Fe 87 B 17 has both the largest Hall angle and magnetoresistance. Co-B and Co-Ni-B have only one third the values found for Fe-B. The Co-Ni-B system is mostly crystalline but the resistivity is nearly as large as the amorphous binary alloys.

Magnetic and transport properties of Co‐Pt thin films

Crystalline films of CoxPt1−x were prepared over the range of x=0.26 to 0.84 atomic fraction by rf sputtering. Magnetization measurements show a wide range of anisotropy conditions including perpendicular anisotropy at intermediate compositions. The magnetic moment per formula unit of Co‐Pt increases with dilution which we attribute to a platinum moment of ≊0.3 μB over the entire range of compositions. The Hall effect and anisotropic magnetoresistance are both large at x≊0.4.

The saturation magnetostriction of thin polycrystalline films of iron, cobalt, and nickel

The saturation magnetostriction λs of Fe, Co, and Ni films was measured by the cantilevered substrate technique. The values of λs, −6.8×10−6 and −38×10−6, obtained for Fe and Ni, respectively, are in accord with bulk published values. A unique value of λs could not be obtained for Co because the sputtered or evaporated Co films were admixtures of face‐centered‐cubic and hexagonal close packed phases and the magnitude and sign of λ varied with the fcc content. Increasing the substrate temperatures during film deposition decreases the fcc content; however, this also caused the development of a C‐axis hexagonal texture normal to the film plane. Annealing the films at ∼500 °C caused a similar but more pronounced texture. Then, because of the uniaxial anisotropy of Co, the films could not be magnetically saturated and the magnetostrictive behavior changed; i.e., the transverse and longitudinal λ were both negative and in some instances the transverse λ was larger than the longitudinal λ.

Amorphous magnetic alloys of cobalt‐titanium

Amorphous cobalt‐titanium films were deposited by r.f. sputtering for titanium content in excess of 14 atom percent. The properties of amorphous CoTi films are similar to those of transition metal‐metalloid glasses: they have soft magnetic properties and their resistivity is in the 100–200μΩcm range. Contrary to most metal‐metalloid glasses, these films have very small magnetostriction, are most thermally stable, and more corrosion resistant.