"This approach breaks through the limits of the current approaches, such as dry or wet etching, and should pave the way for constructing sophisticated architectures of magnetic nanostructures," Vinayak Dravid told nanotechweb.org. "We can easily pattern hard magnetic nanostructures of barium hexaferrite (and similar) with direct-writing, feature size and shape control, and soft matter compatibility."
To demonstrate the technique, the scientists made patterns of barium hexaferrite (BaFe12O19) on a silicon oxide substrate from a precursor "sol-ink" solution of iron nitrate and barium carbonate in ethylene glycol. The team used an atomic force microscope (AFM) cantilever to place drops of the ink at selected locations on the substrate. Then they heated the resulting patterns at 450 °C for four hours and 950 °C for two hours, a heat treatment that converted the precursor into barrium hexaferrite nanoparticles with a mean diameter of about 35 nm.
In this way, the researchers made magnetic nanostructures with dimensions ranging from several hundred nanometres down to 90 nm. The barrium hexaferrite nanoparticles were magnetic, exhibiting a hysteresis loop, a coercivity of 4250 G and a remanent magnetization of 32.2 emu/g.
"This approach may apply to high-density information storage systems, magnetoelectronic sensor devices and so on, but above all it shows the efficacy of the dip-pen nanolithography and sol-gel approach for patterning complex inorganics," added Dravid.
Now the scientists plan to develop a sol reservoir so that they can write more patterns in one go, and to use AFM cantilever tips based on nanotubes to reduce the pattern size. They claim that the technique could provide storage densities of more than 150 Gbit/sq. inch.
The researchers reported their work in Nano Letters.