Nanofabrication of two-dimensional arrays of magnetite particles for fundamental rock magnetic studies

Magnetic measurements of samples with precisely controlled magnetic mineralogy, grain size, and interparticle spacing are needed to provide crucial experimental rock magnetic underpinning for paleomagnetic studies. We report a novel nanofabrication method for producing two-dimensional arrays of cylindrical synthetic magnetite particles with well-defined composition, particle size, and interparticle spacing. The samples are fabricated by writing dot arrays with electron beam lithography, transferring these patterns into sputtered Fe thin films by reactive ion etching in a CO/NH3 plasma, and oxidizing the resulting Fe particles in a controlled atmosphere to form magnetite. Scanning electron microscopy and transmission electron microscopy have been used to monitor the fabrication process and to determine the particle geometry. The particle sizes of our samples range between 100 nm and 265 nm with center-to-center spacings between 180 nm and 310 nm. Low-temperature magnetic remanence data confirm the stoichiometry of the magnetite. We present magnetic hysteresis data and first-order reversal curve diagrams for our samples and compare these with previously published data from other synthetic and natural magnetite samples. The ability to independently control particle size and interparticle spacing of magnetite grains makes our synthetic samples ideal for studying the influence of magnetostatic interactions on the paleomagnetic recording fidelity of naturally occurring magnetite in rocks.