Finite-size scaling analysis of the critical behavior of a general epidemic process in 2D

AbstractWe investigate the critical behavior of a stochastic lattice model describing a General Epidemic Process. By means of a Monte Carlo procedure, we simulate the model on a regular square lattice and follow the spreading of an epidemic process with immunization. A finite size scaling analysis is employed to determine the critical point as well as some critical exponents. We show that the usual scaling analysis of the order parameter moment ratio does not provide an accurate estimate of the critical point. Precise estimates of the critical quantities are obtained from data of the order parameter variation rate and its fluctuations. Our numerical results corroborate that this model belongs to the dynamic isotropic percolation universality class. We also check the validity of the hyperscaling relation and present data collapse curves which reinforce the accuracy of the estimated critical parameters

Highly oriented nonepitaxially grown \u3ci\u3eL\u3c/i\u3e1\u3csub\u3e0\u3c/sub\u3e FePt films

A method of preparing nonepitaxially grown, highly textured L10 FePt thin films is described. A nearly perfect (001) texture was obtained by direct deposition of FePt films on Corning 7059 glass substrates and subsequent rapid thermal annealing. The ordering and orientation of the L10-phase FePt grains were controlled by the initial as-deposited film structure, and also by the annealing process. Magnetic measurements reveal large perpendicular anisotropy for these (001) textured films. The substrates and processes used for nonepitaxial growth of L10 ordered FePt films are much more compatible with practical applications than those grown epitaxially

High coercivity SmFeAlC thin films fabricated by multilayer sputtering

Multilayer sputtering of SmFe/C(Al) plus appropriate thermal processing has been used to fabricate SmFeC thin films with A1 substitution for Fe. It was found that the SmFeAlC thin films exhibited exceptionally high Coercivities. A coercivity of 28 kOe was realized for the thin film with structure of Ta(l000 Å)/|SmFe(40Å)/ C(Al)(5Å)]x50/Ta(200Å) with subsequent annealing at 650°C

High coercivity SmFeAlC thin films fabricated by multilayer sputtering

Multilayer sputtering of SmFe/C(Al) plus appropriate thermal processing has been used to fabricate SmFeC thin films with A1 substitution for Fe. It was found that the SmFeAlC thin films exhibited exceptionally high Coercivities. A coercivity of 28 kOe was realized for the thin film with structure of Ta(l000 Å)/|SmFe(40Å)/ C(Al)(5Å)]x50/Ta(200Å) with subsequent annealing at 650°C

CoPtCr:C nanocomposite films for high density recording

We report results on the magnetic properties of nanocomposite films of the form (Co86Cr14)xPt1-x:C, which were prepared by magnetron sputtering and subsequent annealing. X-ray diffraction shows that these films consist of CoPtCr grains with the face-centered-tetragonal structure embedded in an amorphous C matrix. Magnetic properties such as coercivity (Hc), remanence ratio (S), and coercive squareness (S*) are strongly dependent on the Pt and C composition and annealing temperatures. Compared with previously reported CoPt:C films with a equiatomic Co and Pt ratio, lower exchange coupling and higher S and S* at the same C concentration were obtained. Hc values ranging from 2 to 10 kOe and S close to 1 were achieved for film thicknesses down to 10 nm. These features make CoPtCr:C nanocomposite films very attractive for next-generation high-density recording

Orientation-controlled nonepitaxial L1\u3csub\u3e0\u3c/sub\u3e CoPt and FePt films

We report results on highly oriented, face-centered tetragonal ordered CoPt and FePt thin films grown nonepitaxially by directly depositing films on thermally oxidized Si substrates and subsequent annealing. By controlling the thickness, composition, and annealing conditions, and/or depositing a proper underlayer, nearly perfect (001)-oriented CoPt and FePt films can be obtained. Magnetic measurements reveal large perpendicular anisotropy for such films

Effect of Au spacer layer on \u3ci\u3eL\u3c/i\u3e1\u3csub\u3e0\u3c/sub\u3e phase ordering temperature of CoPt thin films

We have studied the effect of Au on the ordering temperature of CoPt films. The coercivity of the CoPt multilayer with 2 nm Au inserted is around 5 kOe after annealing at 400 °C. This ordering temperature is about 200 °C lower than that of a pure CoPt film. Crystallographical analysis using x-ray diffraction has also revealed that the lattice constant is drastically changed around the same temperature, which is related to the formation of the L10-ordered structure. Thus, the Au plays an important role in reducing the ordering temperature

Effect of Au spacer layer on \u3ci\u3eL\u3c/i\u3e1\u3csub\u3e0\u3c/sub\u3e phase ordering temperature of CoPt thin films

We have studied the effect of Au on the ordering temperature of CoPt films. The coercivity of the CoPt multilayer with 2 nm Au inserted is around 5 kOe after annealing at 400 °C. This ordering temperature is about 200 °C lower than that of a pure CoPt film. Crystallographical analysis using x-ray diffraction has also revealed that the lattice constant is drastically changed around the same temperature, which is related to the formation of the L10-ordered structure. Thus, the Au plays an important role in reducing the ordering temperature

Curie temperature of FePt:B\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e nanocomposite films

We report results on experimental and theoretical studies of structural and magnetic properties of FePt: B2O3 nanocomposite films. It was found for films prepared by magnetron sputtering with subsequent annealing that lattice parameters a and c of fct FePt change with significantly different rates with increase of the B2O3 fraction. As a consequence, fundamental magnetic properties change markedly, with the Curie temperature decreasing by 36% for 25% FePt volume fraction compared with the bulk value. Using an ab initio parametrization of magnetic interactions, we propose statistical model of thermal fluctuations in fct FePt, which explains these observations. Our modeling results demonstrate that the observed phenomena originate in the variation of the exchange interaction parameters with the changes in the c/a ratio. We find that the main factor of this variation is the increase of the difference between the in-plane and interplane exchange interactions as c/a decreases from its bulk value due to stress exerted by the B2O3 matrix