Adam McClure

Ferrimagnetic ordering of single crystal Fe1−xGax thin films

Molecular beam epitaxy was used to deposit body centered cubic single crystal Fe1−xGax thin films on MgO(001) and ZnSe/GaAs(001) substrates well beyond the bulk stability concentration of about 28%. The crystal quality of the substrate surface and each deposited layer was monitored in situ by reflection high energy electron diffraction. The magnetization of the samples as a function of Ga is found to decrease more rapidly than a simple dilution effect, and element-specific x-ray magnetic circular dichroism ascribes this trend to a decrease in the Fe moment and an induced moment in the Ga that is antialigned to the Fe moment.

Properties of single crystal Fe1−xGax thin films

Molecular beam epitaxy was used to deposit single crystal thin film Fe1−xGax samples on ZnSe buffer layers grown on (001) and (110) single crystal GaAs substrates. The crystal quality of the GaAs surface and each deposited layer was monitored in situ by reflection high energy electron diffraction. The magnetic properties of the samples were characterized by vibrating sample magnetometry and ferromagnetic resonance (FMR). The FMR linewidth increases dramatically with Ga concentration while the cubic anisotropy term K1 switches sign.

Single crystal Fe1−xGax thin films for monolithic microwave devices

Modern, high frequency, microwave devices for communications technologies can be made with thin ferromagnetic films with narrow microwave resonance linewidths. Recently, there has been interest in magnetostrictive materials where the material constants can change substantially with stresses and applied magnetic fields. We report the development of single crystal thin (20 nm thick) magnetostrictive films of Fe1−xGax (x = 0.20 FeGa(A), 0.23 FeGa(B), 0.28 FeGa(C) on GaAs(001) substrates and on their use in prototype microwave devices. These Galfenol films have a narrower linewidth than any previously reported similar thin films. We fabricate and characterize novel microstrip-based monolithic microwave devices using Galfenol thin films as an active element. We find a number of important features: (1) There is a large absorption (up to 30 dB/cm) at the resonance frequency. (2) The linewidth of the device is narrow ∼1.5 GHz. (3) The saturation magnetization of the samples decreases with the increase in Ga conte...

Field dependent magnetic anisotropy of Ga0.2Fe0.8 thin films

Using longitudinal MOKE in combination with a variable strength rotating magnetic field, called the rotational MOKE (ROTMOKE) method, we show that the magnetic anisotropy for a Ga0.2Fe0.8 single crystal film with a thickness of 17 nm, grown on GaAs (001) with a thick ZnSe buffer layer, depends linearly on the strength of the applied magnetic field. The torque moment curves generated using ROTMOKE are well fit with a model that accounts for the uniaxial, cubic, or fourfold anisotropy, as well as additional terms with a linear dependence on the applied magnetic field. The uniaxial and cubic anisotropy fields, taken from both the hard and the easy axis scans, are seen to remain field independent. The field dependent terms are evidence of a large affect of the magnetostriction and its contribution to the effective magnetic anisotropy in GaxFe1−x thin films.

Magnetostrictive effect in single crystal Fe1−xGax thin films

The magnetic properties of single crystal Fe1−xGax thin films deposited on ZnSe/GaAs(001) and MgO(001) substrates by molecular beam epitaxy were investigated by vibrating sample magnetometry and angle dependent ferromagnetic resonance. Depositions on the ZnSe buffer layer feature a strong uniaxial anisotropy that scales with the thin film magnetostriction of the samples, while depositions on MgO(001) substrates result in a purely cubic anisotropy whose cubic anisotropy constant, K1, switches sign at a lower Ga concentration than is seen in bulk.

Characteristics of CoxTi1-xO2 thin films deposited by metal organic chemical vapor deposition

This paper deals with the growth and characterization of ferromagnetic cobalt doped TiO{sub 2} thin films deposited by liquid precursor metal organic chemical vapor deposition (MOCVD) using a new combination of the source materials Co(TMHD){sub 3}, tetrahydrofuran (THF), and titanium isopropoxide (TIP). An array of experiments reveals the intrinsic ferromagnetic nature of the grown films, and suggests that the magnetism is not generated by oxygen vacancies.

Magnetic and structural properties of single crystal Fe1−xZnx thin films

Single crystal Fe1−xZnx thin films (x = 0 to 0.85) have been prepared on MgO(001) substrates by molecular beam epitaxy. Reflection high energy electron diffraction monitored the crystal quality of the films in situ and reveals a phase transition of the crystal structure from the α-Fe phase to primarily the Γ phase near a Zn concentration of 40%. Vibrating sample magnetometry shows a lack of any uniaxial anisotropy and a change in sign of the fourth order cubic magnetic anisotropy constant, K1, at a Zn concentration near 40%. The Fe1−xZnx samples maintain the high easy axis remanence and low coercivity of pure iron out to about 40% Zn, at which point the samples show a dramatic increase in coercivity, at least in part due to an increased roughness of the films, as the formation of the Γ phase becomes preferred.