Scanning electron microscope images of cluster ensembles at various magnifications. (Top) Some fragments of film surface; (bottom) the images of cluster ensembles at higher magnifications. (Left) The surface of a film grown for 3 h at full pressure of working gas P = 7 mTorr and at a distance L = 0.65 cm from the target; (right) the surface of a film grown for 6 h at P = 10 mTorr and L = 0.65 cm. Accumulation of stresses near cluster ensembles promotes formation of cracks in thick films, usually passing through ensembles (see lower right).
Examples of the tendency of cluster ensembles to preserve spherical shape.
Diffraction patterns in CrKα-radiation for a-LaSrMnO samples grown at different distances L from the target: (a) L = 0.65 cm; (b) L = 0.95 cm; (c) L = 1.25 cm. On the right [(d)–(f)] is shown the dependence of cluster size (D) on interplane distance (d) corresponding to diffraction maxima in Figs. 3(a)–3(c) , respectively. Icoh and Iincoh are the intensities of coherent and incoherent scattering. Inset in Fig. 3(a) shows a possible two-dimensional model of cluster ensemble containing 7 cluster complexes; each cluster complex includes 7 elementary clusters. Inset in Fig. 3(b) shows two-dimensional fragment of the sample containing one cluster complex of small size and 17 single clusters. Inset in Fig. 3(c) pertains to the presence of only single clusters in the sample.
Temperature dependences of magnetization: (a) for total volume of the sample L = 0.65 cm; (b) for cluster ensembles. In Fig. 4(a) , continuous black line is for paramagnetic sample L = 1.25 cm, H = 6 kOe (ZFC). The inset in Fig. 4(a) shows field dependence of magnetization in FC and ZFC modes for total sample volume (“total”) and for cluster ensembles (“clusters”). In Fig. 4(b) , the M(T) curves for H = 100 Oe and 300 Oe taken from Fig. 4(a) and marked as b, d (FC), and a, c (ZFC), are added.
Magnetic properties of cluster ensembles. (a) Derivative dM/dT determined for temperature range ΔT = 5–17 K in Figs. 4(a) and 4(b) in function of field for total sample volume (“total”) and for cluster ensembles (“clusters”). Black line marks the derivative dM/dT in FC and ZFC modes for paramagnetic sample, L = 1.25 cm. (b) Effect of field on the difference M(FC)-M(ZFC) at different temperatures for total volume of the sample L = 0.65 cm (“for total film”) and for cluster ensembles (“for clusters”). Inset in Fig. 5(b) shows temperature dependences of reciprocal magnetic susceptibility (1/χ) and illustrates increase in the Curie temperature (TC) with field increase.
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