Multiferroics: An Introduction

摘要

Multiferroics: the multifunctional materials exhibit the entwined nature between thetwo distinct phenomena of ferroelectricity and ferromagnetism, which allow them to utilize fornovel device concepts that would not be attainable by either ferroelectric or ferromagneticmaterials. Magnetic and ferroelectric materials are time-honoured research subjects which haveled to new discoveries, both scientific and technological. Multiferroic compounds are the sourceof magnetoelectric (ME) effects that are strong enough to induce magnetic or electric phasetransitions, thus exerting ME phase control. The giant response can be generated by the presenceof exceptionally large magnetic and/or electric fields in matter, which are the result of the long-range ordering. In this sense the ME effect in multiferroics is 'large' if the ME contributioncorresponding to the free energy of the system is large. Due to their interesting physical,chemical, and mechanical properties, these materials have been used to realize a vast number ofdevices ranging from giant devices like electrical transformers to tiny devices like sensors, usedin integrated circuits or as storage devices. Furthermore, these materials are likely to offer newkinds of devices and functionality, because of their size-dependent physical and chemicalproperties, which have motivated a lot of current research activity in the area of ferroelectric andmagnetic materials. In particular, advances in atomic and nanoscale growth and characterizationtechniques have led to the production of modern ferroelectromagnetic materials that reveal arange of fascinating phenomena. These phenomena derived from the fact that electrons have spinas well as charge, giving an extra level of complexity to the physics, and an extra degree offreedom in device design. Magnetoelectric coupling between electric and magnetic orderparameters has been theoretically predicted, and there is intense interest in its implementation indevice architectures taking advantage of these properties. Multiferroics may be in the form ofsingle-phase, exhibit mulitferroicity generally at low temperatures and in a composite form as aproduct property of a composite phase consisting of a magnetostrictive and a piezoelectricmaterial. Hence, the search continues for new single-phase and composite multiferroic materialsthat exhibit high ordering temperatures, high coupling constant, low dielectric loss and lowleakage current.