R. C. Taylor

Magnetic properties of amorphous neodymium–transition‐metal films

Amorphous thin films of NdxCo1−x and NdxFe1−x alloys were prepared over the compositional range 0.08⩽x⩽0.71 by e‐beam evaporation. Magnetization and anisotropy of the samples were studied over a wide temperature range with the aid of a force balance magnetometer, Hall effect measurements, and Mossbauer spectroscopy. It was found that the magnetization of the alloys could not be accounted for by a completely collinear alignment (ferromagnetic) of the Nd and transition‐metal subnetworks. Mean field analysis of the magnetization data showed a large reduction of the Nd–transition‐metal exchange coupling as compared to their Gd analogs. A model was developed which requires that Nd be dispersed in a cone whose axis is parallel to that of the transition‐metal subnetwork by strong coupling to randomly oriented local crystal field axes. This dispersion reduces the Nd net moment to 77% of its free‐ion moment in NdxCo1−x alloys and to 25% of its free‐ion moment in NdxFe1−x alloys. There is evidence that some dispers...

Magnetization and magnetic anisotropy in evaporated GdCo amorphous films

Saturation magnetizations and magnetic anisotropy constants were determined for a series of amorphous GdCo films prepared by thermal evaporation. The films covered the composition range from Gd0.05Co0.95 to Gd0.40Co0.60 and were studied by means of ferromagnetic resonance and a force balance magnetometer. The films, in contrast to those prepared by sputtering, had a hard perpendicular direction of magnetization when Co was less than 91 at.%, and easy and moderate directions within the plane of the film. The anisotropy constant can be expressed in terms of sublattice magnetizations by Ku=0.660MCo2 +2.218MCoMGd+0.097MGd2. The results are explained based on a pair‐ordering mechanism. The composition and temperature dependence of saturation magnetization is essentially the same in evaporated and sputtered films.

Magnetic properties of amorphous Gd‐Fe films prepared by evaporation

Amorphous GdxFe1−x films with 0.18<x<0.33 were prepared by electron‐beam coevaporation of the elements. The composition dependence of anisotropy and the composition and temperature dependence of saturation magnetization of the films were studied. In contrast to evaporated Gd‐Co films, where anisotropy is in‐plane, the Gd‐Fe films were found to have strong perpendicular anisotropy with the uniaxial anisotropy constant (Ku) decreasing monotonically from 3.8×105 erg/cm3 at x=0.18 to 2.0×105 erg/cm3 at x=0.33. The perpendicular anisotropy field (HK) reached a maximum at the compensation composition (x=0.26) and fell off rapidly on both sides. The findings suggest that anisotropy in evaporated films is due to a longer‐range structural ordering than the pair ordering which is assumed to exist in sputtered films. Saturation magnetization measurements showed that magnetization of the amorphous alloys could be closely approximated from the moments of pure crystalline Gd and Fe. The 0 °K moment of Fe was found to b...

Hall effect in amorphous thin‐film magnetic alloys

Amorphous magnetic alloys have unusually large extraordinary Hall coefficients (Rs) defined by the ratio of the Hall resistivity to the net magnetic moment of the alloy. We have studied the Hall effect in amorphous films in the ternary ferrimagnetic systems Co‐Gd‐Mo and Co‐Gd‐Au, alloys which exhibit compensation temperatures (Tcomp). Above Tcomp the Hall coefficient Rs is positive and below Tcomp the sign of Rs changes to negative in a discontinuous manner, probably limited by the homogeneity of the sample. We have also prepared amorphous Gd‐Au and Y‐Co films and measured Rs which we use to qualitatively separate the effects of the Co and Gd sublattices in the ternary alloys. We attribute the sign of Rs to a combined effect of a negative Gd and a positive Co Hall coefficient. Above Tcomp the Co is dominant and points in the direction of the applied field H while Gd is antiparallel to H. Thus, both sublattices contribute in a positive sense to Rs. Below Tcomp the Gd moment is dominant and the sign of Rs i...

Magnetic anisotropy in evaporated amorphous films of the ternary system Gdx(Fe1−yCoy)1−x

Magnetic anisotropy has been determined for evaporated amorphous films of Gdx(Fe1−yCoy)1−x with 0.08<x<0.35 and 0.06<y<0.62. The anisotropy data were fitted with a dipolar equation of the form Ku=J CijMiMj in which Cij is a dipolar coupling constant for the i‐j pair and Mi and Mj are sublattice magnetizations. The model satisfactorily described the experimental data for all films that were amorphous. The anisotropy could be attributed to pair ordering in which rare earth–transition metal pairs (Gd‐Co) and Gd‐Fe) contribute to in‐plane anisotropy and rare earth–rare earth (Gd‐Gd) and transition metal–transition metal (Fe‐Fe, Co‐Co, and Fe‐Co) pairs contribute to perpendicular anisotropy. The Fe‐Co pairs were the strongest contributor to perpendicular anisotropy with CFe‐Co=2.809, CFe‐Fe=0.992, and CCo‐Co=0.660.

Magnetization of amorphous Gd‐Co‐Ni films

The temperature dependence of magnetization from 4.2 to 500 °K for amorphous Gd‐Co‐Ni films obtained by evaporation is found to be satisfactorily described by a two‐sublattice model in wihch the two 3d transition metals form one sublattice interacting antiferromagnetically with the Gd sublattice. The unique magnetization behavior observed is attributed to an intersublattice exchange interaction which is small in comparison to the transition‐metal intrasublattice exchange interaction.

Electrical and Optical Properties of Vapor‐Grown GaP

GaP, both undoped and Se‐ or S‐doped, has been vapor deposited onto the polar 111A (Ga face) and 111B (P or As face) surfaces of GaAs and GaP substrates by means of a PCl3 chemical‐transport method. Hall measurements carried out on the crystals over the temperature range of 77°–500°K and optical spectra taken on as‐grown and zinc‐diffused samples show a pronounced substrate orientation and substrate material effect. Samples grown on GaAs substrates are less uniform than those grown on GaP, and show both a carrier concentration gradient and arsenic contamination. Samples grown on GaP substrates have given electron mobilities as high as 187 cm2/V·sec at room temperature going to 2130 cm2/V·sec at liquidnitrogen temperature. The residual impurity in undoped crystals grown on 111B substrates is shown to be sulfur at a concentration of 2−3×1016 cm−3. Undoped crystals grown on 111A substrates are high‐resistivity p type. Both optical studies and electrical measurements show compensation in the n‐type crystals t...

Mean field analysis of the magnetic properties of vapor deposited amorphous Fe-Gd thin films

The temperature dependence of the saturation magnetization of vapor deposited amorphous Fe‐Gd thin films have been analyzed in terms of the mean field theory. This analysis yielded values of the Fe spin, and the Fe‐Fe and Fe‐Gd exchange interaction energies, which were then correlated to composition. The temperature and composition dependence of other magnetic properties can be calculated from these mean field parameters, and the temperature sensitivity of the saturation magnetization of amorphous Fe‐Gd alloys is shown to be less than that of amorphous Co‐Gd alloys.

Magnetic properties of amorphous GdFeB and GdCoB alloys

Studies have been made of the magnetization of GdFeB and GdCoB amorphous thin films in which ratios of Gd to transition metal and B to transition metal were varied. In GdCoB alloys the Co moment decreases as the sum of the B and Gd concentration increases. Assuming a charge transfer mechanism, each Gd contributes 1.4 electrons and each B 2.1 electrons to the Co 3‐d band. The moment can be described by an additive charge transfer equation. However, in GdFeB alloys the Fe moment increases with increasing B concentration beyond a boron to iron ratio of 0.15. In addition to a reduction in Fe moment by charge transfer of 2.1 electrons from Gd and 2.4 from B, there is an increase in Fe moment due to B addition at higher concentrations. A possible cause for this behavior can be found in the noncollinear (sperimagnetic) alignment of the Fe magnetic sublattice in amorphous ferrimagnetic alloys. High field susceptibility data show that sperimagnetism is reduced with increasing boron.

Angular dependence of GdFe and GdCo FMR spectra

The ferromagnetic resonance spectra of a series of GdFe and GdCo amorphous bubble films have been measured with the static magnetic field H↘s applied at various angles to the film normal. A typical spectrum exhibits two or more peaks. The relative position of these peaks changes as the direction of H↘s is changed in such a way that at some field angles, the peaks may be widely separated, while at others they strongly overlap. To analyze these results, a computer program was developed to find the best fit to these spectra by adjusting the effective anisotropy field Hk′ = Hk‐4πMs and gyromagnetic ratio γ. The effective g‐values obtained agree very well with the Wangness formula, especially if the spectra for H↘s nearly normal to the film are excluded from the computer analysis. In these cases, spin wave excitation renders the determination of the uniform peak position difficult. The multiple‐peak spectra obtained indicate the existence of sample inhomogeneities and the Hk′ and γ values deduced from our anal...