The microstructure and the room-temperature hysteretic magnetic properties of sputtered, 10 nm thin films of equiatomic binary alloys of CoPt and FePt were characterized using transmission electron microscopy (TEM) and a superconducting quantum interference device (SQUID) magnetometer. A transformation from an atomically disordered, face-centered-cubic structure to the L10 ordered structure occurred during postdeposition annealing and was characterized using digital analysis of dark-field TEM images. The transformation was observed to follow first-order nucleation and growth kinetics, and the ordered volume fraction transformed was quantified at numerous points during the transformation. The ordered volume fraction was then compared to the magnetic coercivity data obtained from the SQUID magnetometer. In contrast to the relationship most commonly described in the literature, that the highest coercivity corresponds to a two phase ordered/disordered mixture, the maximum value for coercivity in this study was found to correspond to the fully ordered state. Furthermore, in samples that were less than fully ordered, a direct relationship between ordered volume fraction and coercivity was observed for both CoPt and FePt. The proposed mechanism for the high coercivity in these films is an increasing density of magnetic domain wall pinning sites concurrent with an increasing fraction of ordered phase.

SignificanceIntrinsic and extrinsic properties of ferroelectric materials are known to have strong dependencies on electrical and mechanical boundary conditions, resulting in finite size effects at length scales below several hundred nanometers. In ferroelectric thin films, equilibrium domain size is proportional to the square root of film thickness, which precludes the use of present tomographic microscopies to accurately resolve complex domain morphologies in submicrometer films. We report a subtractive experimental technique with volumetric resolution below 315 nm3, that allows for three-dimensional, tomographic imaging of materials properties using only an atomic force microscope. Multiferroic BiFeO3 was chosen as a model system for illustrating the capabilities of tomographic atomic force microscopy due to its technological relevance in low-power, electrically switchable magnetic logic.

Short reaction times and morphology control in the synthesis of inorganic materials under nonthermal conditions remain a challenge. Herein we report a rapid, self-templating, and nonthermal method based on ultraviolet light to prepare metal oxide hierarchical structures. With this method, the morphology of the metal oxides was controlled readily without using templates.

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Grain growth and ordering kinetics have been studied in a 10-nm-thick CoPt alloy film of equiatomic composition annealed in the temperature range 550–700 °C by quantifying the grain size, grain size distribution, ordered fraction and ordered domain size. The mean grain size of the as-deposited films is 5 nm and the film is fully face-centered cubic. Upon annealing in the temperature range 550–600 °C, the mean grain size reaches a stagnation limit of 27 nm and the grain size distribution is lognormal. Grain growth resumes beyond 600 °C and the mean grain size reaches as high as 55 nm at 700 °C. Ordering occurs by nucleation and growth of L10 ordered domains, with a mean size of 3 nm at 550 °C and 19 nm at 700 °C. The ordered fraction shows a dramatic increase from 1% to ∼28% between the two extremes of annealing temperature. The increase in the coercivity of the annealed films follows the increase in the ordered fraction more closely than the increase in grain size. The shape of the M–H loop shows evidence of coupling between the magnetically hard (ordered) and soft (disordered) regions.