Small angle x-ray scattering (SAXS) method was adopted to investigate the characteristics of growth fractal of two sorts of typical nanoscaled clusters, i.e. g rowing in both ultrafine Ni powders synthesized by chemical reaction and Finemet (Fe73.5Cu1Nb3Si13.5B9) a morphous ribbon by physical crystal lization annealing. The SAXS measurement discloses definitely the existence of d istinct mass multifractal patterns within ultrafine Ni granules and crystallizin g Finemet ribbon. The multifractal spectra of the clusters mentioned above sugge st the occurrence of inhomogeneous distribution of constituent elements and grow th fractal during the formation of those nanoscale clusters. The multifractal sp ectra of ultrafine Ni powders prepared using a variety of procedures take on an obvious difference in shape, indicating the substantial influence of preparation process on diffusion of constituent elements and the growth mechanism of cluste rs. The crystallization annealing processes, however, affect the multifractal sp ectra of Finemet alloy slightly.
B y considering a magnetic system of an ensemble o f nanometer clusters without any external magnetic field, the Monte Carlo simulation o f the Heisenberg model is used t o investigate the transition from a superparamagnetism t o a ferromagnetic single-domain state, which is caused by the growth o f the clusters. W e studied the variation o f the dynamic growth exponent P and the transition critical size o f the cluster N , against the reduced temperature t and the uniaxial anisotropy constant A. W e found that the growth exponent maximized at a certain temperature, other than being taken as a universal constant as some researchers suggested previously.
The electronic structure and absorption spectrum of the wurtzite Zn1-xMgxO(x=0, 00625, 0125, 025) alloys have been calculated by means of the first-principles method. The doping of magnesium leads to an apparent change of the electronic structure of ZnO. The electron density of the oxygen atoms near the magnesium atom increases obviously, and the oxygen atoms transfer some of the electrons to Zn atoms nearby. This weakens the interactions between zinc and oxygen atoms, the band gap becomes broader, which has been validated by the extent of shift of Zn 4s in the same alloys. Theoretical calculation also reveals a blue shift in the absorption spectrum of Mg-doped ZnO, and the absorption edges were located at 379,366,357 and 333nm, respectively, with increasing doping of magnesium in ZnO. The results are discussed in detail.
The Monte Carlo method was employed to perform the numerical simulation for classical discrete diluted Heisenberg spin system driven by an oscillating external magnetic field. To form the diluted spin system based on isotropic Heisenberg model, we introduced in the Hamiltonian of a typical Heisenberg model both random anisotropy energy term characterizing amorphous state with a proportion X and uniaxial anisotropy energy term representing crystalline state with a proportion 1-X. The dynamical transition behavior of the Spin system mentioned above, hysteresis loop scaled with parameter X and random as well as uniaxial anisotropy constant D and A, respectively, was studied in detail. It has been put forward a scaling relationship between hysteresis loop area and parameter X, A and D as below: Aarea-AδDηXσ . The main conclusions can be summarized below:(1)At a specific value X(defined as Xmin), the investigated system gains minimal hysteresis which has been proved experimentally in our another investigation. (2) The exponents δ,η and σ of the diluted spin system are universal constants, and the sum of δ+η(~0.9) equals the exponent δ,η of single either uniaxial or random anisotropy spin system. (3)The specific value Xmin versus logarithm of the ratio of A/D shows a peculiar sigmoidal trend.
The dynamic phase transition has been studied in the three-dimensional kinetic Ising model in the presence of a time-varying(sinusoidal)magnetic field by Monte Carlo simulation.The nature of the transition is characterized by studying the distribution of the order parameter.The system is in contact with an isothermal heat bath at temperature T.We varied the magnitude of the magnetic field,keeping the frequency of the magnetic field unchanged.For the lower values of the environment temperature the transition is discontinuous and it is continuous for higher values of the environment temperature,indicating the existence of a tricritical point (TCP) on the phase boundary.The TCP shifts towards higher temperature region with the decrease of frequency.i.e:TTCP=1.33×e(-ω/30.7)
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