Pyroelectric detection of spontaneous polarization in magnetite thin films
Abstract
We have investigated the spontaneous polarization in Fe3O4 thin films by using dynamic and static pyroelectric measurements. The magnetic and dielectric behavior of Fe3O4 thin films grown on Nb:SrTiO3(001) substrates was consistent with bulk crystals. The well-known metal-insulator (Verwey) transition was observed at 120 K. The appearance of a pyroelectric response in the Fe3O4 thin films just below the Verwey temperature shows that spontaneous polarization appeared in Fe3O4 at the charge ordering transition temperature. The polar state characteristics are consistent with bond- and site- centered charge ordering of Fe2+ and Fe3+ ions sharing the octahedral B sites. The pyroelectric response in Fe3O4 thin films was dependent on the dielectric constant. Quasi-static pyroelectric measurement of Pd/Fe3O4/Nb:SrTiO3 junctions showed that magnetite has a very large pyroelectric coefficient of 735 nC/cm2K at 60 K.
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