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Browsing by Author "Wu, SZ"

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    EFFECT OF SUBSTRATE SYMMETRY ON THE PREFERRED MAGNETIZATION ORIENTATION OF NI FILMS ON CU
    (American Institute of Physics, 1998-06-04) Wu, SZ; Mankey, GJ; Willis, RF; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; United States Department of Energy (DOE); Lawrence Berkeley National Laboratory; University of Alabama Tuscaloosa
    For ultrathin Ni films grown on Cu(100) and Cu(110), the easy axis of magnetization starts out in the plane of the films. Above a critical thickness, the preferred magnetization orientation changes to perpendicular to the films. This behavior is contrary to the spin reorientation transition reported for many thin film ferromagnetic systems where the preferred magnetization orientation starts out perpendicular to the film and then switches to in-plane above a critical thickness. We report in situ surface magneto-optic Kerr effect measurements of the magnetic anisotropy as a function of film thickness. The change in the predominant domain orientation distribution occurs at 8 monolayers (MLs) for Ni on Cu(100) and at 16 ML for Ni on Cu(110). For Ni on Cu(lll) no such change is observed down to 3 ML thickness. These results are discussed in terms of competing surface anisotropy and dipole-dipole energy terms. © 1995, American Vacuum Society. All rights reserved.
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    Growth and magnetic properties of CoxNi1-x and FexNi1-x ultrathin films on Cu(100)
    (American Physical Society, 1997-08-01) Schumann, FO; Wu, SZ; Mankey, GJ; Willis, RF; Louisiana State University System; Louisiana State University; University of Alabama Tuscaloosa
    We have grown ultrathin CoxNi1-x and FexNi1-x films on Cu(100) with varying stochiometry x. We find that these alloy films grow in a fee phase on Cu(100). With the surface magneto-optic Kerr effect we measured the variation of the Curie temperature T-C as a function of the film thickness n in monolayers. Fitting an empirical scaling curve to our results we are able to extrapolate the value T-C(n=x) for samples with different stochiometry. We use this framework in order to determine T-C(n=x) for FexNi1-x alloy films, in particular for concentrations close to 65% Fe content. Bulk Fe65Ni35 shows a collapse of magnetic long-range order and a fcc-to-bce structural transition, which is the so-called Invar effect. In ultrathin Fe65Ni35 films, we observe a ''quenching'' of the Invar effect, because growth on a Cu(100) substrate forces the film to adept the Cu lattice spacing thereby suppressing the structural relaxation.
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    Growth and magnetic properties of FexNi1-x ultrathin films on Cu(100)
    (American Institute of Physics, 1996-08-17) Schumann, FO; Wu, SZ; Mankey, GJ; Willis, RF; University of Wisconsin System; University of Wisconsin Madison; University of Alabama Tuscaloosa
    We have investigated ultrathin FexNi1-x films grown epitaxially on Cu(100) with different stochiometry. With the surface magneto-optic Kerr effect (SMOKE) we measured the variation of the Curie temperature T-C as a function of the film thickness n in monolayers (ML). Using the results of our previous investigations on finite-size scaling (Huang et al.), we are able to extrapolate the value T-C(infinity) for samples with different Fe content. In particular, alloy films with Fe concentrations close to 65% remain ferromagnetic. This is in contrast to bulk Fe65Ni35, which shows a collapse of long range order, which is the so-called invar effect associated with a fcc to bcc structural transition. Growing these alloy films on a Cu(100) substrate forces them to adapt the Cu lattice spacing, thereby suppressing the structural relaxation. (C) 1996 American Institute of Physics.
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    Magnetic behavior of FexNi((1-x)) and CoxNi((1-x)) pseudomorphic films on Cu(100)
    (American Institute of Physics, 1998-06-04) Wu, SZ; Schumann, FO; Mankey, GJ; Willis, RF; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; United States Department of Energy (DOE); Lawrence Berkeley National Laboratory; University of Alabama Tuscaloosa
    We set out to compare the ferromagnetic behavior of FexNi(1-x) and CoxNi((1-x)) films of varying stoichiometry epitaxially grown on Cu(100). The thickness chosen was 5 ML over a wide alloy composition range. Using a scaling law for the thickness vs Curie temperature, we extrapolate the bulk fee film thickness and plot the bulk fee Curie temperature as a function of composition. The results suggest (a) that the Invar effect is quenched in these ultrathin pseudomorphic fee films of FexNi(1-x) alloys and (b) the magnetic phase of Fe atoms is the low-spin ferromagnetic phase. The CoxNi(1-x) films show the expected monotonic decrease in T-c with increasing Ni content. (C) 1996 American Vacuum Society.
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    MAGNETIC-PROPERTIES OF PSEUDOMORPHIC FERROMAGNETIC ALLOY-FILMS ON CU(100)
    (American Institute of Physics, 1995) Mankey, GJ; Wu, SZ; Schumann, FO; Huang, F; Kief, MT; Willis, RF; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; United States Department of Energy (DOE); Lawrence Berkeley National Laboratory; University of Alabama Tuscaloosa
    We report the variation of the thickness dependence of the Curie temperature for a range of ultrathin ferromagnetic alloy films. By simultaneously depositing Fe or Co and Ni on Cu(100) we produce pseudomorphic alloys with controlled stoichiometry. An analysis of the Curie temperature versus thickness curves with an empirical finite size scaling formula reveals that the Curie temperature in the thick film limit increases monotonically with Co or Fe concentration. We compare the bulk alloy Curie temperatures to those of the alloy films extrapolated from the few monolayers limit. © 1995, American Vacuum Society. All rights reserved.
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    SPIN REORIENTATION TRANSITION IN NI FILMS ON CU(100)
    (American Institute of Physics, 1998-06-04) Wu, SZ; Mankey, GJ; Huang, F; Willis, RF; University of Alabama Tuscaloosa
    The magnetic anisotropy of Ni films grown on single-crystal Cu(100) was studied in situ using the surface magneto-optic Kerr effect. The easy axis of magnetization lies in the plane of the film for ultrathin films and it is perpendicular to the film above a switching thickness. This behavior is attributed to a specific contribution to the magnetocrystalline anisotropy energy induced by a change in the film microstructure above a critical thickness. In the Ni/Cu(100) system, the magnetoelastic interface anisotropy favors perpendicular magnetization which becomes comparable to the shape anisotropy at the switching thickness. We compare the switching thickness and magnetization of films grown using different processing conditions.