The past decade has witnessed a thousand-fold increase in magnetic recording areal density, which has revolutionized the way information is stored and retrieved. These advances are the first demonstration of spintronics, which utilizes electron spin, as well as its charge, for information storage, transmission and manipulation. The societal impacts are exemplified by the Nobel Prize in Physics awarded a few months ago to the discovery of the Giant Magnetoresistance (GMR) effect that opened the door to spintronics. As noted by the Nobel committee, the use of GMR can also be regarded “as one of the first major applications of nanotechnology”. Extending from this exciting path, the current project aims at realizing prototype ultrahigh density and data-rate patterned magnetic recording media and memory made of arrays of nanomagnets. Such media will have more than one order of magnitude increase in both storage density and data rate. The success of the project will lead to a new technology in achieving magnetic recording at 1 Terabit/in2 and beyond, enabling numerous new applications.

The project will coordinate two UC research groups with complementary capabilities to develop nanomagnet arrays for information technology applications in future generation ultrahigh density and datarate patterned magnetic recording media and memory. Macroscopic as well as ordered arrays of deep sub-100nm nanomagnets will be made by nanotemplating and e-beam lithography method, respectively. Magnetization reversal mechanisms at such reduced dimensions will be investigated using magnetometry and a novel first-order reversal curve method, in both quasi-static and dynamic regimes. Intrinsic properties of single nanomagnets will be studied using cavity-enhanced magneto-optical Kerr spectroscopy, and compared with the collective responses of the arrays. These studies will allow us to design and realize optimal nanomagnet arrays with controlled ultrafast precessional switching schemes for information storage.

2009 Update:

We have accomplished the following key achievements:
1. “Fingerprints” of nanomagnets: Magnetic configurations in hybrid structures are often difficult to probe when the magnetic entities are buried inside. We have captured magnetic and magnetoresistance “fingerprints” of Co nanodisks embedded in Co/Cu multilayered nanowires using a first-order reversal curve method. In 200nm diameter nanowires, the magnetic configurations can be tuned by adjusting the Co nanodisk aspect ratio. Nanowires with the thinnest Co nanodisks exhibit single domain behavior, while those with thicker Co reverse via vortex states. A superposition of giant and anisotropic magnetoresistance is observed, which corresponds to the different magnetic configurations of the Co nanodisks.
2. Ultrafast dynamics of nanomagnets: We have used time-resolved magneto-optical Kerr effect spectroscopy (TR-MOKE) to measure the dynamics of Fe nanodots in response to a femtosecond laser pulse excitation. This approach is useful to determine the eigenfrequencies of the system, and to intuitively resolve the magnetic evolutions in time domain. We have detected single-domain as well as vortex state dynamics, which have been compared with and explained by micromagnetic simulations.

Societal impacts:
Our results advance the basic understanding of nanomagnetics at reduced dimensions. The arrays of nanomagnets are prototype ultrahigh density and data-rate patterned magnetic recording media and memory elements. Our work have led to several invited talks at top conferences in the field, including the 2008 SPIE-Spintronics meeting, MRS fall meeting, 2009 APS March Meeting, and ICMAT 2009 meeting. There also have been some media coverage, e.g.:

EurekAlert: http://www.eurekalert.org/pub_releases/2009-01/uoc--con012809.php