****NON-TECHNICAL ABSTRACT**** Magnets are widely used in modern technology, from heavy industrial applications to information storage. Ferroelectrics are similar to magnets, but the role of the magnetic field is played by an electric field (they possess "electric polarization"). They are also widely used in applications, such as actuators and certain types of memory chips. Multiferroics are materials combining magnetism and ferroelectricity. They are of interest to scientists, and hold potential for future applications in electronics and solar energy utilization. In this project, two different classes of multiferroics, one based on Mn and Co, and the other on Bi and Fe, will be studied. Determination of the structural and magnetic properties of the first class of these materials will help understand how to make multiferroics with enhanced functional properties. Studies of the second class of materials will also be useful for that purpose, but in addition are expected to establish design principles for novel prototype electronic devices. As an example, a model diode (a common electronic circuit component) with properties controllable by applied voltage will be designed and investigated. Graduate students and young scientists will drive this project, and high-school students will be involved via a pilot nanotechnology program. This project is expected to show ways towards materials with enhanced properties for future electronic and solar energy devices, and to educate young scientists for this important field.
Multiferroics are materials combining magnetism and ferroelectricity. In addition to their scientific interest, they hold potential for applications in electronics, spintronics, and as photovoltaic devices. This project is devoted to two classes of multiferroics; (1) Ca(3)MM'O(6), where M, M? are 3d metals, are novel multiferroics driven by exchange striction. This mechanism is predicted to give rise to giant coupling between magnetism and ferroelctricity. X-ray and neutron scattering will be used to study structural and magnetic properties of these materials with the goal to determine the microscopic mechanism of multiferroicity, and to elucidate the strategy for synthesis of materials with enhanced functional properties. (2) BiFeO(3) is so far the only multiferroic material utilized in model room-temperature devices. Single crystals of BiFeO(3) have only recently become available. Structural and magnetic properties of these crystals will be studied, and the mechanism of the magnetoelectric coupling investigated. Young specialists in neutron scattering techniques (graduate students and a postdoc) will be trained, helping to meet an important need at the new national neutron scattering facilities. This project is expected to show ways towards materials with enhanced properties for future electronic and solar energy devices, and to educate young scientists for this important field.
Magnetic materials are well known for their capacity to store information. Magnetic tape and computer hard drives are examples of this capacity. Materials exhibiting switchable electric polarization (ferroelectrics) are less known. However, they are not less useful, and are also utilized in information storage devices, as well as in various types of sensors and mechanical actuators. Multiferroic materials combine magnetism and electric polarization. Many novel applications, including multistate memories and new sensor types, were proposed for the multiferroics. Unfortunately, no multiferroic compound with suitable characteristics at the room temperature has been found yet. We have investigated bismuth ferrite, which is a multiferroic material promising for room-temperature applications. It has long been believed that at very short length scales, this compound exhibits magnetism suitable for applications, but experimental confirmation was lacking. We have used advanced experimental tools, such as x-ray and neutron scattering, and found unambiguous evidence for the predicted magnetism in this material. In addition, we have demonstrated how the magnetic properties of bismuth ferrite can be manipulated by application of pressure. These observations open new avenues for research that might eventually lead for synthesis of a multiferroic compound suitable for practical applications in sensors and information storage devices. We have also studied atomic structures of metallic compounds based on heavy element iridium. As a result, a new way of manipulating the properties of the electrons that carry electric current was identified. Under some circumstances, these electrons themselves behave as co-aligned little magnets. We have found a new method of switching this magnetism on and off by changing temperature in an otherwise nonmagnetic material. Similar to the case of the multiferroics discussed above, this capability stems from a complex coupling of magnetic and electric properties of the studied compounds. It might be useful for manipulating the magnetic properties of the electrons participating in an electric current, potentially with very little energy cost. Compounds possessing such a capability are sought for making novel energy-efficient electronic devices that use magnetic properties of the current-carrying electrons – the so-called spintronic devices.
