| Using a home-built low temperature piezo-driven magnetic force microscope (LT-PD-MFM), we have studied the magnetic domain behaviors in colossal magneto-resistive (CMR) thin films, the vortex behavior in high TC superconducting (HTCS) thin films as well as the localized penetration depth in a Yttrium(1)Barium(2)Copper(3)Oxygen(7) single crystal.;We have obtained MFM images of domains in CMR films for temperatures from close to TC to far below TC. Domains behave differently for these two temperature zones. Well below TC, neighboring domains exhibit strong interdomain coupling. External magnetic fields can split domains more easily than rearrange them. As temperature increases, domain interactions become weaker with a reduced magnetization, and are subject to moving, splitting or merging. They are still traceable in the presence of a sample scratch. As temperature drops from TC, domains increase in magnetization. The weak interdomain interactions and high fluctuations make domain tracing impossible if there are no topographic defects. Sample scratches tend to pin domains for T ∼ TC. Current flow in CMR films can split domains. This splitting can be both reversible and irreversible when current is turned on and off. Lattice mismatch between a CMR film and a substrate leads to a stress that results in smaller domains. The magnetization of these smaller domains does not cancel out, resulting in "large-scale" domains if detected from a longer distance from the sample.;Images of superconducting vortices in BSSCO films show that they grow with temperature, which is compared with the theory. The theory fits our experimental data well. We also measured the gradient of the levitation force between a magnetic tip and a superconducting single crystal as a function of the tip-sample distance. A series of these measurements were performed at different temperatures. By comparing these data with the theory in which the penetration depth lambda and the TC are parameters to be determined by least-squared fitting, we obtained the local penetration depth lambdaLoc(T) and T C,Loc. We find that the temperature behavior of lambdaLoc(T) is comparable to lambdaBulk(T) measured by another group, but TC,Loc = 83.2 K is substantially lower than TC,Bulk = 92 K measured by SQUID. |
