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Provides information on a study which measured the magnetic properties of nickel/gold multilayer films prepared by magnetron sputtering on glass substrates. Experiment; Results and discussion; Conclusion.

It was shown previously that ultrathin Fe films epitaxially grown on GaAs(001) exhibit a strong in-plane uniaxial magnetic anisotropy which turns out to be a pure interface contribution with an anisotropy constant K[sub U, sup S], expressed as an energy per unit area, which is constant in a wide thickness range. However, for films thinner than ∼10 monolayers (ML), K[sub U, sup S] decreases with decreasing thickness when measured at 300 K. In order to eliminate effects of thermal excitations, Fe(001) films grown on GaAs(001) by molecular beam epitaxy were investigated by superconducting quantum interference device magnetometry at low temperature. The extrapolated room temperature values and the ground state data both indicate that K[sub U, sup S] vanishes at t = 2.5 ML. This is the thickness at which the onset of ferromagnetism takes place, i.e., where the Curie temperature T[sub C] becomes nonzero. This might be interpreted as a verification of the Mermin-Wagner theorem in the sense that long-range ferromagnetic order is stabilized by the magnetic anisotropy. It is discussed whether the onset of ferromagnetism is indeed triggered by the appearance of magnetic anisotropy or if there is a common origin of both phenomena. Finally, it is found that the uniaxial anisotropy does not vanish at T[sub C], but persists up to temperatures of ∼1.5 T[sub C]. This means that K[sub U, sup S] does not scale with a certain power of the spontaneous magnetization. The disparity between the persistence of the anisotropy above T[sub C] and its disappearance below the critical thickness of 2.5 ML is discussed. [ABSTRACT FROM AUTHOR]

The in-plane magnetic anisotropy of Fe films epitaxially grown on GaAs(001), in addition to a thickness-dependent four-fold contribution has a uniaxial component originating from the Fe/GaAs interface. This has been observed in several previous investigations. The orientation of the uniaxial easy axis (e.a.), however, was found to be along the [110] direction in most studies, but also an e.a. parallel to [-110] was reported in a few cases. It has been suggested that different reconstructions of the GaAs surface prior to Fe deposition could be responsible for this discrepancy. In the present contribution, it is shown that in Fe(001) films grown by molecular-beam epitaxy on Ga-rich GaAs(001) surfaces at room temperature the uniaxial anisotropy always has its easy axis along [110] with practically the same magnitude. In particular, the surface reconstruction of the GaAs substrate either (4×2) or (2×6) — has no effect on the resulting uniaxial magnetic anisotropy. This [together with recent results related to the phase transition of Fe/GaAs(001)] suggests that the same atomic configuration is formed at the Fe/GaAs(001) interface in both cases connected with the segregation of a certain amount of As (and Ga) to the surface. [ABSTRACT FROM AUTHOR]

Ultrathin Fe films were epitaxially grown at room temperature on GaAs(001) with either predominant (4x2) or (2x6) surface reconstruction. At nominal Fe coverages of t[sub Fe]>=2.8 monolayers (ML), a ferromagnetic state is observed below a certain critical temperature, T[sub C]. Surprisingly, the magnetic phase transition at T[sub C] appears even sharper than for Fe films on metallic single-crystal substrates, which were believed to be an excellent representation of two-dimensional (2D) ferromagnets. This may be due to the extremely short lateral length scale of film inhomogeneities. The critical exponent β=0.26 is close to the value expected for 2D XY systems of finite size. For t[sub Fe]=3.6 ML, T[sub C] is close to room temperature. T[sub C] decreases steeply with decreasing Fe coverage, with an average slope of 270 K/ML. From a power law extrapolation, T[sub C] seems to vanish at t[sub Fe]=2.5 ML. The onset of ferromagnetism at t[sub Fe]=2.5 ML is interpreted as! a percolation phenomenon during the coalescence process of Fe islands. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The morphology, atomic magnetic moments, and in-plane magnetic anisotropies of ultrathin bcc Fe(001) films deposited by molecular beam epitaxy on ZnSe epilayers grown on GaAs(001) single crystal are reported. The growth mode and structure have been determined in situ by means of reflection high energy electron diffraction and Auger electron spectroscopy. The magnetic properties were characterized ex situ by an alternating gradient magnetometer, superconducting quantum interference device (SQUID) magnetometry, and conversion electron Mo¨ssbauer spectroscopy (CEMS). The Fe growth is epitaxial and occurs by three dimensional nucleation at the beginning. The coalescence of the islands is observed around 7 monolayers (ML). In agreement with SQUID results, CEMS measurements indicate no reduction of the Fe magnetic moment compared to the bulk value even for the first Fe monolayers. Determination of the in-plane anisotropy constants as function of the Fe thickness shows a strong interface-induced uniaxial in-plane magnetic anisotropy, which leads to a continuous evolution from a pure uniaxial anisotropy with easy axis along [110] direction for thickness below 10 ML to the pure bulk cubic Fe anisotropy above 40 ML. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]