Artificial multiferroic heterostructures : Challenges, Need, and Future

The coexistence of electric polarization and magnetization in multiferroic materials provides great opportunities for realizing magnetoelectric coupling, including electric field control of magnetism, or vice versa, through a strain mediated magnetoelectric coupling in layered magnetic/ferroelectric multiferroic heterostructures. The electrostatic tuning of magnetism is particularly important for applications demanded at small length scales, such as nano/micro-electromechanical System (N/MEMS), information storage (magnetic random access memory (MRAM)), highly sensitive magnetometers, RF/microwave tunable devices. One major hurdle in this approach is to develop reliable materials which should be compatible with prevailing silicon (Si)-based complementary metal–oxide–semiconductor (CMOS) technology, simultaneously allowing for small voltage (< 30 V) for the tuning of magnetization switching, i.e. challenge lies in achieving strong ME coupling on ferroelctrically inactive substrates which often clamp mechanical response and cause unmanageable strain conditions. Therefore, the reliable CMOS compatible-integration of ME devices on Si substrates requires elastically/magnetically functional conducting bottom layers which combine high magnetostriction and high electrical conductivity, diminishing the requirement of a separate bottom electrode. Ferromagnetic shape memory alloys (FSMAs) are a new class of multifunctional magnetic materials with a great potential to overcome the aforementioned limitations for ME applications. The FSMA based PbZr0.52Ti0.48O3/Ni50Mn35In15 (PZT/Ni-Mn-In) multiferroic heterostructures on Si substrates demonstrated strong ME coupling (direct and converse) by tuning a comprehensive set of variables such as E- field, H-field, temperature, and stress. Such multiferroic heterostructure have a great potential for the development of unconventional nanoscale memory and refrigeration devices with self-cooling effect and enhanced refrigeration efficiency, thus providing a new venue of their applications.