MIT materials science and engineering graduate student Nicolas M. Aimon has developed new methods of making mutiferroic complex metal oxide thin films by pulsed laser deposition and controlling their magnetic properties. The work could lead to a new generation of smaller, more energy efficient devices for computing and data storage.
In a 2012 paper in Applied Physics Letters, Aimon reported how he grew nanopillars of cobalt iron oxide (CFO) in a matrix of bismuth iron oxide (BFO) on a strontium titanate (SrTiO3) substrate. Of key interest is the coupling between magnetic and electrical properties in these complex metal oxides, with the CFO/BFO nanocomposite film showing promise as part of an electrically-switchable magnetic data storage device. Co-authors were MIT Professor Caroline Ross, and post-doctoral associates Dong Hun Kim and Hong Kyoon Choi.
Because the pillars are magnetic, they could be magnetized up or down, representing zero or one in a storage device. "It's not enough to be able to store information though, you want to also be able to write and read this information," Aimon says. "What we're trying to do is define processes and fabrication techniques that allow us to grow these materials so that the pillars grow where we want them to grow," Aimon says.
Aimon, Ross and other collaborators analyzed the structure of the complex metal oxide films, studied their magnetic characteristics and modeled magnetic switching through application of an electric field, which they have reported in multiple papers. Aimon works in Ross’s Magnetic Materials and Devices Group lab.
Aimon explains that the magnetization in pillars of the ferrimagnetic cobalt iron oxide material, which were grown in a matrix of the ferroelectric material bismuth iron oxide, could be controlled through application of an electric field. An electric field applied to the BFO produces a strain, or mechanical compression of its atomic crystalline structure, which is transferred to the CFO. In the CFO, that strain causes a realignment, or change in directionality, of the CFO's magnetization.
Unlike transistor-based computers in which an electric current drives information flow, "In this case, it's magnetostatic interactions that drive the propagation of information in the material," Aimon says. Magnetostatic interactions are the attraction or repulsion between the north and south poles of magnets. "For all these applications, both the storage and the computation, you need to be able to control the position of the pillars. If they are randomly placed, there is no way you can say, 'read the information, write the information, on this specific location.' The location, that's the basic thing you need to control so you can read and write and define the shapes to be able to make the building blocks, logical blocks."