Fabrication of (Fe,Mn)3O4 ferromagnetic oxide nanostructure using molybdenum nanomask atomic force microscope lithography

Abstract

We reported the fabrication of Fe2.5Mn0.5O4 (FMO) ferromagnetic oxide nanostructure using molybdenum (Mo) nanomask atomic force microscope (AFM) lithography technique for oxide nanospintronics applications. This technique enables us to prepare transition metal oxide nanostructures down to 200nm. The hard x-ray photoemission spectroscopy revealed that the resulting nanostructures preserve a fine electric structure as spintronics oxide same as unprocessed films. The resulting FMO nanostructure showed the magnetoresistance of about −0.11% to −0.14% at the magnetic field of 3000Oe, which value was similar to that of FMO film. These indicate that this technique can construct well defined nanoscale oxides both in structure and physical properties.

Giant Magnetoresistance Observed in (Fe,Mn)3O4 Artificial Nanoconstrained Structures at Room Temperature

“…Above the 100 nm width FMO nanoconstrained structures, the I − V characteristics showed Ohmic linear properties even after forming the nanoconstrained part (parts a and b of Figure ). The results were consistent with those associated with the sizes of FMO-NW structures we previously reported. − Notably, the I − V characteristic of the 50 nm width FMO nanoconstrained structure changed dramatically from a linear to nonlinear property after forming the nanoconstrained part (Figure c) with a strong reduction of current. Since the I − V characteristics exhibited linear properties even in nanoconstrained structures above 100 nm in width, it is not obviously due to process damage at the nanoconstrained structure. , Furthermore, we rule out other possibilities of local heating effect and loss of oxygen at nanoscale.…”

“…The results were consistent with those associated with the sizes of FMO-NW structures we previously reported. − Notably, the I − V characteristic of the 50 nm width FMO nanoconstrained structure changed dramatically from a linear to nonlinear property after forming the nanoconstrained part (Figure c) with a strong reduction of current. Since the I − V characteristics exhibited linear properties even in nanoconstrained structures above 100 nm in width, it is not obviously due to process damage at the nanoconstrained structure. , Furthermore, we rule out other possibilities of local heating effect and loss of oxygen at nanoscale. (Fe,Mn) 3 O 4 is a semiconductor with election type carrier, and heating effect and loss of oxygen for this material cause enhancement of current due to decrease of resistance and increase of carrier concentration.…”

“…19 In this Letter, we have fabricated well-defined and more complicated nanoconstrained structures of (Fe,Mn) 3 O 4 (FMO), which is a very high temperature ferromagnetic oxide semiconductor, using two different steps involving atomic force microscope (AFM) lithography, originally developed by our team, and measured their electric and MR properties at room temperature. In the first step we placed an epitaxial ferromagnetic oxide nanowire (NW) in the nanoarea, which was selected by AFM tip scanning using a Mo nanomask liftoff technique (oxide deposition type 18,19 successive second step we reduced an oxide NW width at the selected point with higher controllability using a Mo nanomask AFM lithography technique (oxide removal type 20,21 ). Figure 1 shows a schematic illustration of the fabrication of a FMO nanoconstrained structure.…”

“…The results were consistent with those associated with the sizes of FMO-NW structures we previously reported. [18][19][20][21] Notably, the I-V characteristic of the 50 nm width FMO nanoconstrained structure changed dramatically from a linear to nonlinear property after forming the nanoconstrained part (Figure 3c) with a strong reduction of current. Since the I-V characteristics exhibited linear properties even in nanoconstrained structures above 100 nm in width, it is not obviously due to process damage at the nanoconstrained structure.…”

Enhancement of Spin Polarization in a Transition Metal Oxide Ferromagnetic Nanodot Diode

“…Furthermore, to make sure of electronic structure after the process of Mo lift-off, we have also conducted hard X-ray photoemission spectroscopy (HX-PES). As shown in ref , the HX-PES spectra of Fe:2p core levels and valence bands show that the ratio of Fe 2+ and Fe 3+ in each spectrum does not change in unprocessed and processed FMO films, indicating that Mo nanomask lift off does not give a significant change in the oxidation state. Moreover both valence band spectra also did not change.…”