Amitava Gangulee

Amorphous ferromagnetic thin films

Amorphous ferromagnetic thin films containing one or more transition metals and one or more glass formers have been fabricated by sputtering. Typical magnetic properties of these thin films are comparable to those of bulk amorphous alloys with corresponding compositions. Thermal stability and annealing characteristics of these amorphous thin films are discussed.

Preparation and properties of coevaporated amorphous Co‐Zr thin films

Co1–xZrx thin films (5<x<35) were prepared by coevaporation in a two E‐beam source system on glass substrates held at 30 °C. The crystallinity of all films were monitored by x‐ray diffraction techniques; the films in the composition range x⩾7.4 were found to be amorphous. Magnetization, hysteresis loop, and FMR measurements were carried out with these Co‐Zr films. The saturation magnetization as a function of composition shows similar trends as in the Co‐Ti thin films. The FMR spectra were rather complex with four to six modes for perpendicular resonance; the most intense mode gives a value for 4πMs close to the static data. The other modes at higher resonance fields may be caused by preferential oxidation of Zr or a large negative anisotropy induced by oxidation. Auger and ion probe profile analysis of the Co‐Zr films indicated the presence of oxygen throughout the bulk of these films. SEM examination of some of these Co‐Zr films showed the existence of a columnar structure, and it is possible that oxyge...

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.

Magnetocrystalline anisotropy in epitaxially grown (Gd,Tm,Y)3(Fe,Ga)5O12 garnet thin films

Single‐crystal thin films of gallium‐substituted mixed garnets (Gd,Tm,Y)3(Fe,Ga)5O12, grown by liquid phase epitaxy, have been used as drive layer materials in contiguous disk bubble devices; a critical parameter for the selection of a specific composition is the value of the magnetocrystalline anisotropy constant K1. We have measured the values of K1 in a series of epitaxial thin films grown on (100) and (111) oriented gadolinium gallium garnet substrates. K1 in the (100) oriented films were measured both by ferrimagnetic resonance and with an inductive hysteresigraph, whereas only resonance measurements were employed in the (111) oriented films. The values of K1 for each composition, obtained by different methods from films with different orientations, agree reasonably well with each other and are consistent with what would be expected from linear extrapolation of the K1’s of pure rare‐earth iron garnets after an empirical correction for gallium substitution.

Annealing behavior of amorphous ferromagnetic Co‐Fe‐B and Fe‐B thin films

The annealing behavior of amorphous Co‐Fe‐B and Fe‐B thin films, fabricated by rf sputtering in an argon plasma, have been investigated. The magnetostrictive Fe‐B films exhibit a perpendicular anisotropy in the as‐deposited condition, but after a stress relief anneal an in‐plane anisotropy is obtained. An in‐plane easy axis develops in the as‐deposited Co‐Fe‐B thin films. The in‐plane anisotropy direction in both sets of films can be rotated by annealing in an external magnetic field aligned parallel to the hard axis via a thermally activated process. Preannealing with a magnetic field aligned parallel to the easy axis stabilizes these films to a significant extent. The kinetics of easy axis rotation has a simple logarithmic dependence on time. Analysis of the kinetics of easy axis rotation indicates that preannealing apparently increases the thermal activation energy for this rotation process.

Abstract: Magnetocrystalline anisotropy in mixed garnet thin films

We have measured the values of K1 in films grown on (100) and (111) oriented gadolinium gallium garnet substrates from PbO:B2O3:Fe2O3 fluxed melts. The values of K1 for each composition, obtained by different methods from films with different orientations, are consistent within themselves but are significantly smaller in magnitude than what would be expected from linear extrapolation of the K1’s of pure rare earth‐iron garnets. (AIP)

Abstract: Annealing behavior of amorphous ferromagnetic Co‐Fe‐B and Fe‐B thin films

The annealing behavior of amorphous Co‐Fe‐B and Fe‐B thin films, fabricated by RF sputtering in an Ar plasma, has been investigated. (AIP)