The continuous research and development into new materials and structures has made possible the massive technological progress in digital consumer electronics, computing power and data storage capacities. Using a combination of vertical integration via thin film deposition techniques and photolithography, more complex sensors, integrated circuits, displays and recording devices are created with current lithographic definition limits at around 40 nm and precise thin film deposition of layers less than 1 nm thick. The quest for creating smaller and more powerful devices with less power consumption pushes solid-state physics and materials science to new frontiers. In this respect, multiferroic materials are very promising candidates for the development of advanced sensors and technologies because they uniquely exhibit simultaneously magnetic, electric and piezo properties.

The electric and magnetic phases that coexist in a multiferroic material can couple to each other directly or via strain mediated effects leading to the occurrence of the magneto-electric (ME) coupling. The ME coupling can be induced either magnetically or electrically and this effect is described by the ME coupling coefficient. The measurement and modelling of the ME coupling of multiferroics is highly complex and requires the development of specialized equipment currently unavailable. NPL has developed brand new metrology for the measurement of the magnetically induced ME coupling coefficient of multiferroics. Our experimental approach focused on both: bulk multiferroics as well as nano-structured multiferroics. One of the unique experimental systems designed and developed at NPL is a room temperature measurement of multiferroics based on the quasi-static piezoelectric coefficient measurement under applied magnetic field.

Schematic diagram of the Berlincourt experiment for combined d33 and α31 measurements. The same waveform is used for the AC load system and the AC Helmholtz coils.

The extension of our multiferroic metrologies to micro / nano scale spatial resolution through the realization of a unique SPM based approach will provide NPL with the world's first fully traceable measurement system for multifunctional, multiferroic materials used for the next generation of smart sensors and actuators. Among some of the technological applications envisaged for multiferroic materials NPL has proposed a novel magneto-electric magnetic recording reader used to read back data in hard disk drives or magnetic tapes.

Publications

• Multiferroic composite for combined detection of static and alternating magnetic fields
  M. Vopsaroiu, M. G. Cain, G. Sreenivasulu, G. Srinivasan, A. M. Balbashov
  Materials Letters, 66, pages 282-284 (2012)
• Voltage control of the magnetic coercive field: multiferroic coupling or artefact?
  M. Vopsaroiu, M. G. Cain, P. D. Woolliams, P. M. Weaver, M. Stewart, C. D. Wright, Y. Tran
  Journal of Applied Physics, 109, 066101 (2011)
• Emerging Technologies and Opportunities Based on the Magneto-Electric Effect in Multiferroic Composites
  M. Vopsaroiu, J. Blackburn, M. G. Cain
  Novel Materials and Devices for Spintronics book series: Materials Research Society Symposium Proceedings (invited paper), 1183, pages 151-162 (2010)
• Composite multiferroics as magnetic field detectors: How to optimise magneto-electric coupling
  J. Blackburn, M. Vopsaroiu, M. G. Cain
  Advances in Applied Ceramics, 109 (3), pages 169-174 (2010)
• Emerging Technologies and Opportunities Based on the Magneto-Electric Effect in Multiferroic Composites
  M. Vopsaroiu, J. Blackburn, M. G. Cain
  Mater. Res. Soc. Symp. Proc. (invited paper), 1161 (2009)
• Experimental determination of the magneto-electric coupling coefficient via piezo-electric measurements
  M. Vopsaroiu, M. Stewart, T. Hegarty, A. Piniella, M. G. Cain, G. Srinivasan
  Meas. Sci. Technol., 19, 045106 (2008)
• Multiferroic magnetic recording read head technology for 1Tb/in2 and beyond
  M. Vopsaroiu, J. Blackburn, A. Piniella, M. G. Cain
  Journal of Applied Physics, 103, 07F506 (2008)
• Tuning the Magneto-electric Effect of Multiferroic Composites via Crystallographic Texture
  M. Vopsaroiu, M. Stewart, T. Fry, M. G. Cain, G, Srinivasan
• IEEE Trans. Magn., 44 (11), pages 3017–3020 (2008)
• Verified finite element simulation of multiferroic structures: solutions for conducting and insulating systems
  J. Blackburn, M. Vopsaroiu, M. G. Cain
  Journal of Applied Physics, 104, 074104 (2008)
  A new magnetic recording read head technology based on the magneto-electric effect
  M. Vopsaroiu, J. Blackburn, M. G. Cain
  J. Phys. D: Applied Physics, 40, page 5027 (2007)