The work in WP1 was comprised in two individual tasks (T). T1, Magnetoelectric composite deposition and characterizations using IMEC nanofabrication facility in 200mm clean room to optimize the device material properties; T2, Developing a reliable method to quantify the ME effect in different ME composite in scaled device geometry.
A particular focus was given on understanding and defining individual material components in a ME composite. For the piezoelectric component to generate strain, an in-house optimized recipe for the growth of PZT or Lead Zirconate Titanate (Pb[Zr(x)Ti(1-x)]O3) was used by using SOLMATE’s pulsed laser deposition tool. To deposit different magnetic materials (Ni, NiFe, FeGa, CoFeB), sputtering method was optimized and ferromagnetic resonance, vibrating sample magnetometry were used to characterise them. To complement these studies, additional characterization methods like peak force microscopy, atomic force microscopy, X-ray diffraction, sheet resistance measurement, scanning electron microscopy etc. were also performed.
The task T2 is one of the key findings of MUST. To evaluate a ME coupling in a ME composite, MUST devised a model based on anisotropic magnetoresistance measurement by four probe technique in a fringe capacitor geometry. This method allows to probe the ME effect by biasing two dc pads when the sample is rotated under a constant saturating external magnetic field and quantify how much magnetoelectric anisotropy field is generated per voltage. This parameter gives an estimation of how strong the ME coupling is in a particular ME composite.
In the WP2, knowledge gained from WP1, was used to fabricate fringe capacitor type micron size devices and were characterised by two very sensitive optical technique, a. Brillouin Light Scattering (BLS) and Femto-second Laser Time Resolved Magneto-optic Kerr Effect (TR-MOKE). By BLS, spin wave band by ME transduction was measured. The key observations were: 1. SW band modes were successfully generated by ME effect which correspond to phonon/acoustic modes. 2. SW modes are highly localized. By TR-MOKE, magnetization dynamics induced by ME effect were probed in time domain by using a pico-second pulse pump-probe technique in a CoFeB/PZT composite. The key finding are: 1. Magnetization dynamics were mapped in time and spatial domain and a complex magnetization dynamics were observed which could be mimicking the strain/phonon propagation in the PE domain, 2. The magnetization mode seemed to have a wavelength of ~ 1μm and velocity ~4200ms-1 which matches the phonon velocity in the magnetic domain. This has a potential implication of phonon-magnon coupling which can enhance the ME coupling in a composite.
