Isolated and interactive arrays of magnetic nanostructures as small as 15 nm are fabricated using nanolithography and related technologies, and are characterized using magnetic force microscopy. It has been demonstrated that manipulating the size, aspect ratio, and spacing of these nanostructures can lead to unique control of their magnetic properties. A quantum magnetic disk based on discrete single-domain nanomagnetic structures with storage density of 65 Gbits/in. 2 is demonstrated along with a low-cost method for mass producing such disks. Other impacts that nanofabrication can bring to the development of future magnetic storage are discussed.

Metal rings with inner diameters of 1 and 5 m, fabricated using electron-beam lithography, were used to calibrate magnetic force microscopy ͑MFM͒. A MFM tip's effective magnetic charge, q, and effective magnetic moment along the tip's long axis, m z , can be determined from the MFM signal of the ring at a different scan height and a different electric current in the ring. The magnetic moments in the directions transverse to the tip's long axis were estimated by a straight current wire. It was found that for a Si tip coated with 65 nm cobalt on one side, q is 2.8ϫ10 Ϫ6 emu/cm, m z is 3.8ϫ10 Ϫ9 emu, and m x and m y are in the order of 10 Ϫ13 emu, which are negligible compared with m z. Furthermore, the MFMs sensitivity to the second derivative of the magnetic field was determined from the minimum ring current for a measurable MFM signal to be 0.1 Oe/nm 2 .

The switching behavior of isolated nanoscale nickel and cobalt bars, which were fabricated using electron-beam lithography, was studied as a function of bar length. The bars have a 35 nm thickness, a 100 nm width, and a length varying from 200 nm to 5 m. Magnetic force microscopy showed that except for the Ni bars with a length equal to or less than 250 nm, all other as-fabricated bars were single domain. Unlike the bar width dependence, the switching field of the single-domain bars was found to first increase with the bar length, then decrease after reaching a peak. The peak switching field and the corresponding bar length are 640 Oe and 1 m for Ni and 1250 Oe and 2 m for Co, respectively. The nonmonotonic length dependence suggests that the magnetization switching may be quasicoherent in the short bars and incoherent in the long bars, and that the exchange coupling is much stronger in Co bars than in Ni bars. Furthermore, the switching field of 1-m-long Co bars was found to increase monotonically as the bar width decreases, reaching 3000 Oe at a 30 nm width.

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Metal rings with inner diameters of 1 and 5 m, fabricated using electron-beam lithography, were used to calibrate magnetic force microscopy ͑MFM͒. A MFM tip's effective magnetic charge, q, and effective magnetic moment along the tip long axis, m z , can be determined by the current flowing in the ring. The magnetic moments in the directions transverse to the tip's long axis were estimated by a straight current wire. It was found that for a silicon tip coated with 65 nm thick cobalt on the side, q ϭ 2.8 ϫ 10 Ϫ6 emu/cm, m z ϭ 3.8 ϫ 10 Ϫ9 emu, and m x ϭ m y ϭ 10 Ϫ13 emu, which are negligible compared with m z. Furthermore, the tip's sensitivity to the second derivative of the magnetic field was found to be about 0.1 Oe/nm 2 .

Quantized magnetic disks consisting of an array of single domain Ni pillars with a density of 18 Gbits/in.2 were fabricated using nanoimprint lithography (NIL) and electroplating. The total disk area, limited by the NIL mold, is 4 cm×4 cm, leading to a total 45 Gbits. Magnetic force microscope (MFM) images show that all pillars 70 nm in diameter and 400 nm in height are single domain. The magnetostatic interaction between adjacent pillars is fairly strong. The pillars have an average switching field of 360 Oe and can be switched by a MFM tip with a large magnetic moment.

Nanoscale spin-valve structures with a width as small as 70 nm were fabricated using nanoimprint lithography and ion milling or lift off. The spin-valve multilayers consisting of NiFe(10 nm)/Co(1 nm)/Cu(13 nm)/Co(10 nm)/NiFe(2 nm) were deposited using direct current sputtering. The effects of device size, as well as fabrication process on domain structures, switching fields, switching field variation, and giant magnetoresistive ratio were investigated using scanning electron microscopy, atomic force microscopy, magnetic force microscopy, and magnetoresistance measurements.

Ahsttact -Quantized magnetic disks (QMDs)consisting of longitudinal single-domain Ni bars with densities from 3 Gbits/in2 to 10 Gbits/in2 were fabricated using nanoimprint lithography and a lift-off process.Two different types of MFM tips were used in the writing and reading process, one for erasing and writing, another for reading; both were magnetically 'hard'.The QMDs were first erased by aligning all bars with the write-tip scanning the entire sample, then written using lithography software in NanoScope 111. Error-free results were obtained up to 7.5 Gbits/in2 despite the poorly-defined magnetic field from the write-tip and despite not having a feedback control for the write-tip position.