San Jose, CA, November 22, 2005 -- Calit2 Fellow and UCSD Physics graduate student, Zhi-Pan Li received a "Best Poster" award at MMM2005 - the 50th Magnetism and Magnetic Materials Conference, held October 30 - November 3 in San Jose, CA. The award is given to recognize excellence in research and presentation.
"This is probably the most important magnetism meeting in the world. The recognition by the community of Mr. Li's work is certainly an honor for him and a source of pride for me," said Ivan K. Schuller, Professor of Physics and Li's faculty advisor. "Li was a Calit2 fellow and this work could not have been done without the support of Calit2."
Li is a member of Schuller's Thin Film Laboratory Nanoscience Group, where they work with objects on the nanometer scale. (One nanometer [nm] is one-billionth of a meter.) The thin film group is involved in research in a variety of condensed matter physics problems, developing and studying the structure and properties of novel materials. Group webpage
Nanotechnology crosses the fields of physics, chemistry, engineering, biology and many subdisciplines. It is expected to make a significant contribution to the fields of computer storage, semiconductors, biotechnology, manufacturing and energy in the not to distant future. Scientists in this field typically work with devices that are less than 100 nanometers in size. By comparison, a strand of human hair is 80,000 nanometers wide.
Thin films are the basis for a large number of technologies and are one of the most important tools for the preparation of novel materials. Magnetic nanometer scale objects (thin films) have attracted much attention during the past few decades, in part because of their necessity in modern data storage devices, but also due to their new interesting physical phenomena. When the size of magnetic materials is reduced to the order of 10-100 nm, their magnetic properties become increasingly dominated by factors which vary depending on the direction of the measurement, such as shape and surface anisotropy. When ferromagnetic (FM) nanoelements are combined in arrays the magnetostatic interaction among the individual objects must also be considered. Depending on size and shape, different spin configurations can be found. These objects are very important in a number of applications, such as sensors and media for magnetic recording, the automotive and aerospace industries.
The problem that Li and his colleagues address in the winning poster presentation is a fundamental problem in the exchange bias, and in the magnetism community as a whole, which is the relevance of important length scales, and how they govern the system properties. Specifically, they investigated how antiferromagnetic domain size is modifying the exchange bias structures (ferromagnet [FM] and antiferromagnet [AF] heterostructure). However, the magnetic signal in an antiferromagnet is usually very weak, and its sizes are usually very difficult to measure using conventional methods. Therefore, the method that they use is to compare the antiferromagnetic domains with something else, and see how they interact, by which they hope to gain information about the antiferromagnet itself.
Two things were used for the comparison: 1) FM domain wall width (which is well documented, and easily measurable), and 2) after nanostructuring FM, the antiferromagnet domain size is compared with FM nanodot size. The interaction can be clearly seen, and consequently, they are able to see and demonstrate how different competitive mechanisms can modify the system structure.
Li is "very happy to receive this award. It is a recognition of our work." He will be completing his doctoral work and receiving his Ph.D. in Physics sometime next year.
Domain Size Relevance in Exchange Biased Nanostructures. Z. Li, R. Morales, O. Petracic1, and I.K. Schuller.
Nanostructured ferromagnetic (FM = Ni, Co) dots were prepared on top of epitaxial antiferromagnetic (AF) FeF2 continuous film grown on MgF2(110) substrates, and studied by Magneto-Optical Kerr effect (MOKE). In a judiciously chosen intermediate cooling field, when the FM is in the form of continuous film, the sample exhibits coexistence of positive and negative exchange bias. This is in contrary to the averaging effect observed on samples grown on MgO(100) substrates. This effect is explained in terms of the AF subsystem size as compared with the some characteristic FM length scale, probably its domain wall width. However, direct evidence relating to their actual sizes, especially the AF subsystem size, is still lacking. Nanostructuring the FM on top of continuous AF film provides a direct probe of the AF subsystem size at different cooling conditions. The result is further supported by micromagnetic simulations. This work is supported by the US-DOE.
Nanoscience Group at UCSD