Magnetoelectric measurements of multiferroic thin film materials using microwave microscopy

We have developed a technique to quantitatively measure the magnetoelectric (ME) coupling effect in multiferroic materials using microwave microscopy operating at 1 GHz. The technique is used to measure the piezovoltage induced by an external magnetic field through the non-linear dielectric constant. The unique tip geometry of the microscope allows measurement of the ME coupling from a sample region as small as 1 micron cube without the use of a bottom electrode. AC magnetic field up to $\sim $ 10 Oe is used. We have demonstrated the measurement on different types of multiferroic films. In particular, PbTiO$_{3}$-CoFe$_{2}$O$_{4}$ nanocomposite thin films consisting of nanograins of PbTiO$_{3}$ embedded in the matrix CoFe$_{2}$O$_{4}$ was found to exhibit enhanced ferroelectric properties and robust ferromagnetism. The ME coefficient as large as 4 V/cmOe was observed in the nanocomposites at room temperature. Enhancement in the ME effect due to the mechanical resonance of the substrate was observed at $\sim $100 KHz.