Magnetic interactions in nanostructured films

Magnetic interactions in nanostructured films are important topics for understanding micromagnetism. They play significant roles in recording media and magnetic random access memory (MRAM). Due to measurement sensitivity limitations, arrays of hundreds of elements must be fabricated to obtain a high enough signal-to-noise ratio. The results are often clouded by statistical variations such as dot shape, size, and spacing. Thus, more sensitive techniques are needed to probe magnetism on this scale. In this thesis, a high-resolution magnetic force microscope (MFM) and an ultra-sensitive microcantilever torque magnetometer (MTM) are developed to study the magnetic interactions in nanostructured films and patterned nanostructures. Higher resolution MFM is demanded for studying domain structures of nanostructured films. It requires a further development of the magnetic tips. To improve spatial resolution, high coercivity CoPt MFM tips were modified by focused ion beam milling, leaving a 30 nm sized magnetic particle on the tip end. Recording media with a density as high as 1100 kfci (kilo flux change per inch) can be well resolved and a resolution around 10 nm has been achieved. High-resolution tips were used to study the domain structure of perpendicular magnetic recording (PMR) media after ac- or dc-erasure. Our measurements demonstrate that ac-erasure is a better preconditioning method due to a better periodic bit structure. Our measurements also show that magnetic clusters (∼80 nm) can be broken up into smaller domains (∼25 nm), which indicates that the magnetic grains are only weakly coupled in this PMR media. An ultra-sensitive MTM was set up to characterize the magnetic properties of one or a few elements. A sensitivity as small as 1 x 10−15 Am2 has been achieved at room temperature in air. Our results, when correlated to the MFM observations and micromagnetic simulations clearly indicate that a magnetostatic interaction exists between the close paired submicron-sized permalloy bars. The interaction makes the antiparallel magnetization directions of paired bars a stable state. The magnetostatic interactions of closely spaced single-paired bars have been observed for the first time