J. Sztern

Frequency‐dependent complex permeability in rare earth‐substituted cobalt/nonmagnetic transition metal soft ferromagnetic amorphous thin films

Using radio frequency (rf) sputtering, we have prepared in presence of a static magnetic field, ferromagnetic thin films of composition (Co93Zr7)100−yREy(RE=Nd,Pr,Dy,Tb... a magnetic rare earth element). This study was performed for small amounts of RE substitution (0<y<3). These films exhibit attractive soft magnetic properties similar to CoZr alloys: low coercivity (Hc∼1 Oe), and a high saturation induction (4πMs≳10 kG). A low in‐plane uniaxial anisotropy Hk was induced, whose magnitude depends upon the composition and the preparation parameters. Substitution by RE atoms affects essentially the μ frequency‐response. Depending on the nature, the concentration of RE atoms and on the value of Hk, a high relative rotational permeability μ (μ’∼500–3000 at frequencies up to 500 MHz) was obtained. Also depending on RE and on y, high μ‘ (μ‘∼400–3000 at ν∼1 GHz) distributed over a very broad frequency range (Δν∼500–2500 MHz) could be measured.

Static and dynamic magnetic properties of (CoZr)100−x(RE)x amorphous thin films

The saturation magnetization, uniaxial anisotropy, and the dynamical magnetic properties of amorphous (Co92Zr8)100−x(RE)x thin films have been studied for various magnetic rare earths and for 0≤x≤3. The films were rf sputtered in presence of a dc magnetic field applied parallel to the film plane. For RE=Nd, Pr, Dy, and Tb, the films exhibit an in‐plane uniaxial anisotropy Ku, the magnitude of Ku being related to the particular RE. When RE=Gd and Sm a biaxial anisotropy develops constituted by a Ku and a perpendicular anisotropy Kp. The resonance linewidth as a function of x and RE is also reported.

Field induced anisotropy in amorphous Co100−xTix thin films

Co100−x Tix amorphous thin films were deposited by rf sputtering in the presence of a magnetic field applied parallel to the film plane. The deposition parameters were determined in order to obtain films with negligible perpendicular anisotropy Kp, small coercive field Hc, and a well‐defined in plane uniaxial anisotropy Ku. When the rf input power Ip is higher than a critical value, Kp is developed via a columnar structure, and for Ar pressure PAr higher than 3×10−3 Torr, Hc shows a large increases. Samples deposited under optimal conditions (Ip =100 W, PAr =3×10−3 Torr) present soft ferromagnetic properties and a large value of Ku, with 1.2×104<Ku <2.5×104 erg/cm3 for 7.5<x<16, Ku decreasing with decreasing Co content. The results suggest that Ku should be induced during the deposition process if one wants to obtain a large field induced anisotropy.

Induced magnetic anisotropy related to the local atomic order: A study in amorphous Co‐Zr and Co‐Zr‐M thin films

The in‐plane uniaxial anisotropy Ku, induced by a magnetic field applied during the deposition, was investigated in amorphous thin films of Co1−xZrx and Co1−x−yZrx My (M=Ti, Nb, and Pt) obtained by rf sputtering. For a given concentration Ku presents a bell‐shaped variation as a function of Ar pressure PAr. The critical pressure for which the maximum value of Ku is obtained and the absolute value of (Ku)max changes for the various alloys. These results and the high value of (Ku)max are explained by a model where (Ku)max is related to the local anisotropy via the local structure upon the nonmagnetic metal. (Ku)min is essentially related to a pseudodipolar short‐range order.

A study of complex permeability in rare earth‐substituted cobalt/nonmagnetic transition metal amorphous thin films

By using radio‐frequency (rf) sputtering, amorphous ferromagnetic thin films of composition (Co93Zr7)100−yREy (RE=Nd, Pr, Dy, Tb, Gd, or Sm: magnetic rare earth elements) have been prepared. This work was performed for small amounts of RE substitution (y<3). These films exhibit static soft magnetic properties similar to CoZr alloys. For all compositions studied, a low in‐plane uniaxial anisotropy Hk appears, whose magnitude depends upon composition and preparation parameters. Above a critical substitution level, a biaxial anisotropy exhibiting an in‐plane Hk and a perpendicular component Hp is measured for films containing Gd or Sm. The substitution by RE atoms essentially affects the frequency‐response shape of complex permeability, depending on nature, concentration of RE atoms and on values of both Hk and Hp. High‐frequency permeability spectra could be well fitted by a theoretical model based on magnetization changes due to rotation, using a composition‐dependent Landau–Lifshitz damping term. The resu...

The field induced magnetic anisotropy in amorphous Co-RE alloys films

The properties of the coherent anisotropy, formed by applying a magnetic field in the film plane during deposition, were studied in amorphous (Co/sub 1-y/Zr/sub y/)(RE)/sub x/ thin films, for various RE and deposition parameters. When RE=Pr,Nd,Dy and Tb an in-plane uniaxial anisotropy K/sub u/ is developed. The variations of K/sub u/ versus x, RE and measuring temperature are well explained by a single-ion anisotropy mechanism. The change of K/sub u/ with P/sub Ar/ and deposition temperature T was studied on Co/sub 95-x/Zr/sub 5/Dy/sub x/ films and for 5 22 films with isotropic magnetic properties are obtained at T/sub d/ higher than T/sub crit/=f(x). Structural investigations show that K/sub u/ is related to sites containing CoDy pairs. The data are explained by a model based on the bond orientational mechanism: In samples prepared at low T/sub d/, K/sub u/ is related to the individual deformations of sites, while when thermal fluctuations are important, directional correlations of the sites are formed. The peculiar results observed for RE=Sm and Gd are due to the intrinsic properties of these RE. >

In‐plane anisotropy induced by rare gases in RE‐Co amorphous films

Postdeposition annealing of some sputtered rare‐earth–cobalt (YCo3, GdCo, and HoCo) amorphous films in an atmosphere of rare gases Ne, Ar, Kr, and Xe has been shown to induce a strong in‐plane anisotropy Ku?−5×105 erg/cm3. Also, after the rare‐gas anneal, the coercive force and the resonance linewidth are remarkably reduced and one observes in YCo3 films a well‐defined spin‐wave spectra which obeys well the quadratic‐dispersion law. The presence of in‐plane anisotropy in the annealed films is tentatively attributed to the formation of Co‐Co pairs along the thickness.

Exchange dominated surface modes in amorphous ferromagnetic YCo3

Abstract The ferromagnetic resonance spectra, in the band Ku of sputter deposited YCo 3 amorphous films, show the presence of a surface mode which is due to a thin surface layer which forms at the initial stages of the deposition process. A simple model of two exchange coupled films enables us to determine as a function of temperature the magnetic properties and the effect of thickness of this surface layer. Induced anisotropy K u in the bulk of the film and the thin surface layer has opposite signs and a comparative study of K u = f(T) and the relaxation mechanism suggests that the origin of the K u in the two cases could be different.

Easy axis and easy plane magnetization in D.C. sputtered amorphous YCo3 films

The presence of a transient layer growth of about 500 A thick in D.C. sputtered amorphous YCo3 films has been detected by a study in the range 4–300 K of ferromagnetic resonance in films of thickness in the range 0.05 to 1.0 μm. The surface mode observed in films e≳0.2 μ transforms into the uniform one for e=0.05 μ. A model of exchange coupled layers explain the results observed. From relaxation process and Bloch law dependence of 4πMS, it is seen that cobalt in the transient layer at the substrate film interface could have an ionic character and in the rest of the film a metallic one. We propose that the transient layer might have a higher Ar content leading to a strong in plane anisotropy. This was verified by subjecting films to an annealing at 200 °C for 24 h in pure Ar atmosphere which indeed induces a very strong in plane anisotropy KU=−5.105 ergs cm−3 at 300 K irrespective of film thickness. This in our opinion is the first direct demonstration of the effect of Ar to induce KU<0.

In‐plane uniaxial anisotropy, coercivity, and magnetic aftereffect of CoZrDy amorphous films

Amorphous alloy thin films of (Co95Zr5)100−xDyx with a well‐defined in‐plane uniaxial anisotropy Ku were prepared by rf sputtering. The saturation magnetization, Ku, and the coercive field were studied as a function of temperature and for the composition range 4≤x≤20. Ms could be fitted by the molecular‐field model, Ku interpreted by a single‐ion anisotropy process, and Hc by a model of Alben, Becker, and Chi [J. Appl. Phys. 49, 1653 (1978)]. At low temperatures (T≤50 K) and for the whole concentration range a new type of aftereffect is observed, the main characteristic of which is described.