Writing and reading 7.5 Gbits/in2 longitudinal quantized magnetic disk using magnetic force microscope tips

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 III. 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