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Chemically synthesized FePt nanocrystals can exhibit room temperature ferromagnetism after being annealed at temperatures above 500 [degrees]C. In thick films composed of FePt nanocrystals, the coercivity can be quite large. However, the coercivity of thin films has been found to decrease significantly with decreasing thickness, to the point that ferromagnetism at room temperature is lost. We studied 12 to 55 nm thick films by using magnetic force microscopy (MFM) under external applied fields. We made smooth films by spin casting 4-nm-diameter FePt nanocrystals and annealing them at 605[degrees] C-630[degrees]C. Thin FePt films showed lower coercivity than thick films. To help interpret the MFM images, we obtained complementary magnetic and structural data by superconducting quantum interference device (SQUID) magnetometry, transmission electron microscopy (TEM), and X-ray diffraction. We conclude that the magnetic properties of these films are strongly affected by nanocrystal aggregation that occurs during annealing. Index Terms--FePt, magnetic force microscopy (MFM), nanocrystal, sintering.

This study has investigated the anisotropy in the flat, in epitaxial thin-film samples. La2/3Ca1/3MnO3 floods on substrates of SrTiO3 (STO) whit orientation (001), dueto the good adjustment presented in the parameters network of LCMO and STO (with aparameter mismatch of 1%). The samples were deposited using the technique DC reactive sputtering at high pressure oxygen, with a thickness of 150 nm working at a temperature of 850°C and oxygen at a pressure of 3.5 mbar. The structure was obtained from magnetic domains through Magnetic Force Microscopy (MFM). Varating the applied field at a 200K below the Curie temperature (TC). Additionally, magnetization cycles were obtained for temperatures of 80K, 200K and 250K and measures of magnetoresistance fields of 88 Oe, 230 Oe, Oe -44, -88 Oe, Oe -144, and -331 Oe. The distribution and the size of the domains were correlated with the cycles of magnetic hysteresis and magnetoresistance measures. This Paper allows us to conclude that the magnetic hysteresis is the result of changes in the assembly of the magnetic domains in response to the externally applied field. [ABSTRACT FROM AUTHOR]

van der Waals (vdW) materials have shown unique electrical and optical properties depending on the thickness due to strong interlayer interaction and symmetry breaking at the monolayer level. In contrast, the study of electrical and tribological properties and their thickness-insensitivity of van der Waals oxides are lacking due to difficulties in the fabrication of high quality two-dimensional oxides and the investigation of nanoscale properties. Here we investigated various tribological and electrical properties, such as, friction, adhesion, work function, tunnel current, and dielectric constant, of the single-crystal α-MoO 3 nanosheets epitaxially grown on graphite by using atomic force microscopy. The friction of atomically smooth MoO 3 is rapidly saturated within a few layers. The thickness insensitivity of friction is due to very weak mechanical interlayer interaction. Similarly, work function (4.73 eV for 2 layers (hereafter denoted as L)) and dielectric constant (6 for 2L and 10.5-11 for >3L) of MoO 3 in MoO 3 showed thickness insensitivity due to weak interlayer coupling. Tunnel current measurements by conductive atomic force microscopy showed that even 2L MoO 3 of 1.4 nm is resistant to tunneling with a high dielectric strength of 14 MV/cm. The thickness-indifferent electrical properties of high dielectric constant and tunnel resistance by weak interlayer coupling and high crystallinity show a promise in the use of MoO 3 nanosheets for nanodevice applications.