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August 23, 2010

Progress to Colossal Magnetoelectricity and Denser Hard drives

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(a) The transverse spiral Mn magnetic order found in many multiferroic perovskite manganites. Here the Mn spins rotate around an axis defined by the cross product Si×Si+1, while the magnetic propagation Q is parallel to the vector joining these two spins ri,i+1. The direction of the ferroelectric polarization is given by the cross product P=(Si×Si+1)×Q. In the same figure the O atoms (red circles) are coherently displaced from their paraelectric position by a distance d (depicted as white circles) and are related to the Dzyaloshinskii vector by Di,i+1~λd×ri,i+1 , where λ is the spin-orbit coupling constant. (Adapted from [2].) (b) A depiction of a weak ferromagnetism generated from a DM interaction from a small canting of antiferromagnetic spins that are stacked along the c axis. For clarity only one column of spins along the c axis is shown. In this arrangement the Dzyaloshinskii vector changes sign between pairs of spins. A team of scientists at Rutgers University has found a material in which an electric field can control the overall magnetic properties of the material. If the magnetoelectric effect discovered by the Rutgers group can be extended to higher temperatures, it could be useful for manipulating small-scale magnetic bits in ultra high-density data storage.

Towards colossal magnetoelectricity?



Physical Review Letters - Cross-Control of Magnetization and Polarization by Electric and Magnetic Fields with Competing Multiferroic and Weak-Ferromagnetic Phases


From our investigation of magnetoelectric properties of a multiferroic phase in Eu0.75Y0.25MnO3 competing with a weak-ferromagnetic phase in magnetic fields, we found intriguing hysteretic behaviors of physical properties with variation of temperature and magnetic field. These hysteretic behaviors arise from the kinetic arrest (dearrest) processes of the first-order multiferroic-weak-ferromagnetic transition, resulting in frozen (melted) magnetoelectric glass states with coexisting two phases. Tipping the delicate balance of two competing phases by applying electric and magnetic fields leads to a remarkable control of magnetization and electric polarization.

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