CHARACTERIZING NEW LOGIC DEVICES BASED ON NANOMAGNETISM
Samuel Bowden, Ursula Gibson, and John Unguris
As nanotechnology for computing advances, new mechanisms for performing logic functions are being sought to not only increase the density and speed of data manipulation but to introduce added capabilities such as low power dissipation, reprogrammability, nonvolatility, and radiation hardness, which complement the efficiency of devices at this scale. Logic devices based on nanomagnetic interactions have been the focus of much research in the past decade since they fulfill these requirements at room temperature and may easily be integrated with existing information technology. Magnetic elements have long been implemented for data storage in, e.g., hard drives and core memory, but the ability to perform computations via magnetic interactions presents an opportunity to integrate computing with memory in ways that will lead to applications such as smart memory and personal computers with no boot-up times.
A magnetic logic scheme was tested that consists of arranging thin film Ni80Fe20 ring structures that store data as the chirality of a circular vortex magnetization state: either clockwise (CW) or counterclockwise (CCW). Logic functions are accomplished by linking multiple rings together such that one ring induces a vortex state of opposite chirality to its neighbors via magnetic exchange interactions and the propagation of localized areas of spin reorientation (domain walls). To enable rapid characterization of a ring’s magnetic state and deterministic behavior, a technique for modifying the Magneto-Optic Kerr Effect (MOKE) signal from a reflected laser beam was developed. Since the vortex state of a ring has net-zero magnetization regardless of its chirality, it is necessary to break the symmetry of the MOKE signal. This was accomplished by applying single layer antireflection coatings to either the top or bottom half of a ring. Light reflected from coated Ni80Fe20 has an enhanced MOKE signal contrast and phase shift, leading to hysteresis loops with unambiguous signatures of the vortex state chirality.
To characterize a structure’s magnetization with high spatial resolution, Scanning Electron Microscopy with Polarization Analysis (SEMPA) is used to directly image and quantify the magnetic spin structure with 10nm resolution. SEMPA has been used to characterize the development of other nanomagnetic logic systems and will be used to aid in the development of magnetoresistance-based sensors that detect the spin structure and movement of domain walls through magnetic nanowires.