Synthesis and Characterization of Magnetic Nanowires Prepared by Chemical Vapor Deposition

Various metal silicide and germanide magnetic nanowires were synthesized using a home-built CVD [chemical vapor deposition] system. The morphology, composition, and magnetic properties of the nanowires were studied and correlated with growth parameters such as temperature, pressure, time, and source-substrate distance.

One of the compositions targeted for synthesis was MnSi [manganese silicide]. In bulk, this material orders helimagnetically at T_c [curie temperature] = 30K, with a helical pitch of about 20 nm. After extensive study, we learned that the thickness of the silicon dioxide layer on the substrate is a critical parameter for the growth of MnSi nanowires. An oxide assisted one-dimensional growth mechanism was proposed. A growth diagram was created that shows the effect of various growth parameters on the products. The nanowires were characterized magnetically in a SQUID [superconducting quantum interference device] magnetometer using AC [alternating current] susceptibility. These measurements confirmed helimagnetic ordering and skyrmion lattice formation in the nanowires.

Another composition targeted for synthesis was FeGe₂ [iron digermanide]. In bulk, FeGe₂ undergoes a spin density wave transition at 289 K. Nanowires of FeGe₂ have not been previously reported. We were able to grow FeGe₂ nanowires on a Ge substrate. The FeGe₂ nanowires were identified by selected area diffraction using a transmission electron microscope. The growth direction was determined to be [110]. FeGe₂ nanowires were integrated into four-probe nanodevices, which were fabricated through an e-beam lithography system via beam dose correction and a double-layer geometry. The combined magnetic and electronic transport measurements show that while the antiferromagnetic spin density wave is still present along the FeGe₂ nanowire long axis, ferromagnetism was identified in other directions.