HRTEM and EELS Studies of L1<SUB>0</SUB>-Ordered FePt nano-Clusters on MgO Films Prepared Below 673 K

Abstract

Three kinds of FePt-MgO granular films were prepared by a vacuum successive deposition of MgO, Pt, Fe and MgO on a cleaved surface of sodium chloride below 673 K. Their microstructures, electronic structures and magnetic properties were studied by high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS) and measurement with a superconducting quantum interference device (SQUID) magnetometer. The TEM observations and selected area electron diffraction patterns revealed that the samples mainly consist of few nm-sized FePt clusters embedded in MgO films with L1 0 -ordered structure and c-axis perpendicular to the film surface. Size effect on the stability of L1 0 phase in the FePt nano-clusters was directly observed in [MgO/Fe(0.38 nm)/Pt(0.30 nm)/MgO] and the critical size of the transition from L1 0 to A1 phase was estimated as around 2 nm, that can be considered as smaller than effective size for the transition from ferromagnetism to superparamagnetism. Coercivity of [MgO/Fe(1.0 nm)/Pt(0.8 nm)/MgO] was 1:2 Â 10 5 A/m. The Fe-L 2;3 white-line ratios of the present samples measured by EELS were about 4.0, independently on the incident direction of electron beam. The higher white-line ratio may be attributed to their high-spin state by a change of 3d-band structure owing to the hybridization of d-bands between Fe and Pt atoms.

Preparation of strain-included rutile titanium oxide thin films and influence of the strain upon optical properties

“…The substrate was a cleaved (001) surface of sodium chloride (NaCl) that was separated 3 cm from a target, and the substrate temperature was 350°C measured by a thermocouple. After the deposition, a thermal treatment for crystallization of the titanium oxide film was performed at 350°C for 0.5 h at an oxygen pressure of 4.0 × 10 − 4 ∼ 0.25 Pa [11,12] and then cooled gradually at a rate of 10°C/min [13]. The titanium oxide thin films thus prepared were supported on a copper-microscopic grid covered with a collodion film after dissolving the NaCl substrate on a water surface.…”

Size effect on the ordering ofL10FePt nanoparticles

“…3,4 Recently a few studies have reported that equiatomic FePt is not transformed into the equilibrium L1 0 order phase when its size is less than several nanometers. [5][6][7][8][9][10][11][12] For example, Takahashi et al 5 evaluated the long-range order parameter S of FePt granular films and found that the critical size for ordering was d ϳ 3 nm, being somewhat larger than the thermodynamic calculation using optimized nearest-neighbor Lennard-Jones potentials. A very similar critical size has been reported in thermodynamic calculations 9 and Monte Carlo simulations 11 based on the regular lattice Ising model.…”

Oxygen release and structural changes in TiO2 films during photocatalytic oxidation

“…11,12 The film was then cooled gradually to room temperature at a rate of 10°C / min. 13 The titanium oxide thin films were supported on a Cumicroscopic grid covered with a collodion film following the dissolution of the NaCl substrate that was performed with water. The hydrocarbon materials were deposited subsequently with 30 nm thickness by a chemical vapor deposition a͒ Electronic mail: h046105d@mbox.nagoya-u.ac.jp or a41263a@nucc.cc.…”