Four MOF crystals identified as ‘multiferroic,’
Metal-Organic Frameworks (MOFs) are crystalline, porous polymeric materials, consisting of metal ions linked together by organic bridging ligands to form one-, two-, or three-dimensional structures that can be porous. MOFs can be thought of as a three-dimensional grid in which the vertices are metal ions or clusters of metal ions that are connected to each other by organic molecules called linkers. The choice of metal and linker has significant affects on the structure and properties of the MOF. For example, the metal’s coordination preference influences the size and shape of pores by dictating how many ligands can bind to the metal and in which orientation. ZIF-8 is a commercially available metal-organic framework (MOF) and MOF-500 is a new metal–organic framework (MOF). Some of the applications of MOFs are storage of gases such as hydrogen and carbon dioxide, gas purification, gas separation, catalysis and sensors.
Multiferroics are materials in which at least two of the ferroelectric, ferro/antiferromagnetic and ferroelastic phases coexist. ((Ferromagnetism means a material possesses magnetic poles, while ferroelectricity refers to a material that possesses positive and negative electrical charges that can be reversed when an external electrical field is applied.) Though the mechanisms that allow ferroelectricity and ferromagnetism seem to be incompatible, there are a select few materials in which ferroelectricity and ferromagnetism are both present, namely Cr2O3, yttrium- iron-garnets, boracites, rare-earth ferrites and manganese-based perovskites. In these materials, the ferroelectric and ferro/antiferromagnetic phases are coupled in such as way as to produce a cross phenomenon known as the magnetoelectric (ME) effect. This allows manipulation of the magnetic phase with an external electric field and/or manipulation of the electric phase with external magnetic field. The integration of the ME effect into device technology would have substantial implications, however the above mentioned single phase materials exhibit prohibitively small ME effect.
Source: http://shell.cas.usf.edu/fml/multiferroic.html
Four MOF crystals identified as as ‘multiferroic,’
Two of the Florida State University’s scientists Naresh S. Dalal and Sir Harold W. “Harry” Kroto, took a close look at a family MOFs and found that four such crystals possessed properties that rarely coexist. The scientists arrived at their findings by employing both laboratory experimentation and computational analysis.
Prof. Dalal, Florida State’s Dirac Professor of Chemistry and Biochemistry said, “We identified these four crystals as ‘multiferroic,’ meaning that they are simultaneously ferromagnetic and ferroelectric in nature when cooled to a specific temperature. Normally, these two properties are mutually exclusive. Most materials are either ferromagnetic or ferroelectric based on the number of electrons in the ion’s outer electron shell. Therefore, finding four multiferroic materials at one time is quite scientifically significant and opens numerous doors in terms of potential applications.”
Referring to the potential use of these multiferroic materials in the creation of high-powered computer memories and other data storage devices that can hold far more information than is currently possible, Prof. Kroto, a Francis Eppes Professor in Florida State’s Department of Chemistry and Biochemistry said, “Theoretically, it might be possible to design devices that are much smaller and faster than the ones we use today to store and transmit data. And with data split over two mediums, information could be encrypted in a way that makes it far more secure than is currently possible. This could have wide-ranging applications in areas as diverse as the aeronautics industry, the military, the workplace and even the average consumer’s home.” Prof. Dalal added high-tech devices made from these materials would have far less environmental impact. He said, “The four new multiferroic crystals that we have identified all substitute other, less toxic metals for lead, which is a potent neurotoxin. By reducing the amount of lead that enters landfills, we also reduce the amount that enters our water supply — and our bodies.”
In addition to Prof. Dalal and Prof. Kroto, other collaborators from Florida State were Ronald J. Clark, an emeritus professor of chemistry and biochemistry who continues to conduct research; Prashant Jain, a graduate research assistant; and Vasanth Ramachandran, a graduate teaching assistant. Additional researchers were Haidong Zhou, an assistant scholar/scientist at the National High Magnetic Field Laboratory in Tallahassee; Anthony K. Cheetham, Professor of Materials Science and Metallurgy at the University of Cambridge in England; and Brian H. Toby, a senior physicist at Argonne National Laboratory in Illinois.
Prof. Kroto is one of three recipients of the 1996 Nobel Prize for Chemistry and Biochemistry for his co-discovery of buckminsterfullerene, a form of pure carbon better known as “buckyballs.”
Prof. Dalal was recognized in 2007 as one of the top scientists in the southern United States by the Memphis Section of the American Chemical Society, which selected him to receive its Southern Chemist Award.
Source: http://www.fsu.edu/news/2010/02/11/crystal.research/
February 12, 2010