Organic materials have proven to be important for electronics by virtue of being cheap, environmentally friendly, flexible, easy to process and offering virtually unlimited variations of functionality. They are also promising for spintronics, a branch of electronics that employs spin degrees of freedom in electronic devices. MRSEC researchers at the University of Nebraska and their colleagues at the University of Puerto Rico have shown that a new layer of functionality, called ferroelectricity, can be added to the repertoire of spintronic devices based on organic materials [Nano Lett. 11, 599 (2011)]. Using sophisticated computations the researchers conceived and studied an organic tunnel junction consisting of two magnetic metal electrodes separated by an thin layer of the organic ferroelectric material poly(vinylidene fluoride), or just PVDF. The electrical resistance of the junction depends on whether or not the magnetic electrodes are magnetized parallel or anti-parallel to one another. Because of this the magnetic state of this junction can be used as a unit of memory. The new level of functionality added to this junction is provided by the nature of the organic insulating barrier: the orientation of PVDF molecules can be reversed by application of an electric field, a property known as ferroelectricity. The researchers found that this switching leads to a significant change in electrical resistance. This property of the organic tunnel junction makes a unique multifunctional device which can be switched by a magnetic field and/or an electric field to produce four different memory states.
Atomic structure of an organic tunnel junction. On the left and right are the magnetic leads and in the middle is the organic ferroelectric material PVDF.