J. Schelleng

Magnetostriction of amorphous TbxFe1−x thin films

A systematic investigation was made of magnetostriction and magnetization in amorphous thin films (∼1 micron) of TbxFe1−x with x=0 to 0.5 prepared by electron‐beam co‐evaporation. The amorphous or crystalline character of the films was determined using x‐ray and Mossbauer techniques. Net magnetization, coercivity, and the initial in‐plane and out‐of‐plane distribution of magnetization was determined using a vibrating sample magnetometer. Both the sign and magnitude of the magnetostriction was measured as a function of magnetic field using a capacitance method. Over most of the concentration range the amorphous samples have a positive magnetostriction with a maximum of Δl/l=285×10−6 at x=0.4 and going to zero at the compensation point (x=0.22) and near x=0.5 where the amorphous alloys are no longer magnetically ordered at room temperature. In the region x=0.1 to 0.2 the magnetostriction is more complex, being negative for fields up to 5 kOe and positive at higher fields. All the films studied with x?0.1 we...

Fabrication and radio frequency characterization of high dielectric loss tubule-based composites near percolation

Microscopic lipid tubules with an average aspect ratio (length/diameter) of approximately 12 were metallized electrolessly with copper or nickel-over-copper, and mixed with vinyl to make foot-square composite dielectric panels. As loadings increased the metal tubule composites displayed an onset of electrical percolation with accompanying sharp increases in real and imaginary permittivities. Gravity-induced settling of the tubules while the vinyl was drying increased true loading density at percolation threshold for nickel/copper tubules to ∼12 vol %. This threshold was at a significantly lower loading density than that previously measured for percolation by composites containing spherical conducting particles. Qualitatively, the shape of the composite permittivity versus loading density curves followed predictions by the effective-mean field theory for conducting stick composites. Changes in permittivity of the vinyl panels were observed for several days after fabrication, and were apparently associated ...

Amorphous YFe2—A concentrated spin glass

Magnetic susceptibility, Mossbauer, and neutron scattering studies of the same alloy sample all indicate that amorphous YFe2 (a‐YFe2) exhibits spin‐glass behavior with a truly thermodynamic spin‐glass transition at TS.G.=58K. These studies show that spin‐glass behavior can persist to quite high magnetic concentrations in an amorphous alloy system which is dominated by competing ferromagnetic and antiferromagnetic exchange interactions. At a lower temperature of T?20K, the susceptibility versus T curve shows a break and the coercive field is anomalous. We interpret this phenomenon near T=20K as arising from magnetic ’’blocking’’ of individual spins or regions of correlated spins which persist below TS.G.. This produces a cluster‐freezing‐type ’’pseudo‐transition’’ which is merely a manifestation of the slowing down of spin fluctuations to a time interval comparable with the experimental susceptibility measurement time. The temperature dependence of the spin‐glass order parameter is obtained from the suscep...

Magnetic properties of substituted M-type hexagonal ferrites

We have studied the BaFe12-2xMxTixO19 system where M = Co, Ni and Zn and 0 < x < 1. We have measured static and dynamic properties of single crystal platelets. We find that Co introduces a strong temperature dependence of the magnetic anisotropy field Ha, and large intrinsic magnetic relaxation, but Ni and Zn do not.

Hydrogenation and magnetic properties of amorphous rare‐earth‐iron (R‐Fe) alloys

A novel film synthesis procedure is used to explore the amounts of hydrogen absorbed by amorphous a−R1−xFex alloys with 0≤x≤0.9 and R=Gd, Dy, Tb, Ho, Y. Magnetization and Mossbauer measurements on a‐Gd1−xFex: Hy are illustrative of the dramatic magnetic changes produced by the hydrogen. For a‐Gd1−xFex: H3 the compensation temperatures are reduced by about 200 K and the Curie temperatures by 50 K. Detailed analysis of magnetization M(T) data for a‐GdFe2: Hy with y=0, 1.25, and 3.0 are presented to demonstrate the changes of magnetic moments and exchange parameters. JFe‐Fe and JFe‐Gd exhibit small percentage decreases with added hydrogen whereas JGd‐Gd has a large change, going from ferromagnetic (y=0) to antiferromagnetic coupling (y=3). The iron moment increases by about 10%. The magnetic changes are interpreted in terms of charge transfer as mediated by anionic behavior of the hydrogen.

A new magnetic amorphous alloy system: (Fe,Co)‐bismuth

We have synthesized, for the first time, amorphous alloy films of (Fe,Co)1–xBix. The amorphous alloys are most stable in a narrow composition range near x = 0.20, while above or below this composition (for 0.10⩽x⩽0.30), a predominant amorphous alloy along with Fe or Co and Bi metal is observed. The alloys are ferromagnetic and magnetization data indicate that the Fe or Co moments are little affected by the Bi content near x = 0.20 and are at least 95% of that for the pure magnetic metals. For the Fe‐Bi alloys, a detailed characterization was made using x‐ray, magnetization, Mossbauer, FMR, and differential scanning calorimetry (DSC) techniques. The DSC measurements show irreversible exothermic or combined exothermic‐endothermic transitions over narrow temperature ranges up to 830 K. Their magnetization versus temperature plots exhibit discontinuous changes associated with the DSC transitions and Curie temperatures near 1020 K. The films display large uniaxial anisotropies perpendicular to the film planes....

FMR in some amorphous Re ‐ 3‐d transition metal films

Ferrimagnetic Resonance (FMR) and vibrating sample magnetometer (VSM) measurements were made on amorphous GdCo3 and Gd‐, Ho‐, Tb‐ and DyFe2 for temperatures from 90 to 500K. For Gd alloys, the T dependence of the linewidth is in general agreement with that predicted for a T independence Landau‐Lifshitz damping parameter of ∠198/s. Ho‐ and TbFe2 and to a lesser degree the Gd alloys show inconsistencies between the FMR and VSM values for the magnetization.

Hydrogen in amorphous magnetic rare earth-transition metal alloys

Abstract A wide range of hydrogenated amorphous rare earth-transition metal (R-T) alloys has been synthesized using a newly developed vapor deposition synthesis procedure. Measured H/R ratios vary from 2 to 5 depending on composition. The R-T films do not fracture or disintegrate when activated as do crystalline alloys. Magnetic and electrical results are given for the a-Gd x Fe 1−x system. The inclusion of hydrogen sharply reduces the compensation temperature by 200K and the Curie temperature by 50K at a given composition. The dominant magnetic effect is a reduction of the GdFe exchange interaction. Potential application advantages of hydrogenated amorphous R-T alloys are also discussed.

Magnetic properties of Gd1−xFex films

The saturation magnetization, M, g‐value, exchange and magnetic damping parameter were measured in films of Gd1−xFex, where 0<x<1, as a function of temperature and frequency using ferromagnetic resonance (FMR) and vibrating samples magnetometer techiques. We find for x∠.9 that the dominant exchange coupling is between the Fe‐Fe ions. The exchange‐conductivity linewidth broadening mechanism is minimal in this sytem.

Microwave properties of GdFe2:H3 films

Ferromagnetic resonance (FMR) fields and linewidths of amorphous GdFe2:H3 films have been measured for temperatures from 6 to 500 K at x band. A special procedure was devised in order to introduce and maintain hydrogen gas in films of GdFe2. Magnetometer measurements were performed on the same films. We find that for GdFe2:H3 the magnetization goes through a compensation point near T=300 K and the Neel temperature is 450 compared to 500 K for unhydrided GdFe2. The g factor obeys the Wangsness relation as a function of temperature. The FMR linewidth ΔH is proportional to 1/M except for 20