The general approach for the consideration of the magnetoelectric effects in ferroic nanorods is proposed in the framework of the phenomenological theory. The intrinsic surface stress, magneto- and electrostriction as well as piezoelectric and piezomagnetic effects are included into the free energy. The intrinsic surface stress under the curved nanoparticle surface is shown to play an important role in the shift of ferroelectric and ferromagnetic transition temperatures and built-in magnetic and electric fields appearance, which are inversely proportional to the nanorod radius. We consider the case of quadratic and linear magnetoelectric coupling coefficients. The linear coupling coefficient is radius independent, whereas the quadratic ones include terms inversely proportional to the nanorod radius and thus strongly increase with decrease of the radius. The predicted giant relative dielectric tunability in the vicinity of ferromagnetic and ferroelectric phase transition points induced by quadratic magnetoelectric coupling increases by 2-50 times. The quadratic magnetoelectric coupling dramatically changes the phase diagrams of ferroic nanorods when the radius decreases. In particular the second order phase transition may become a first one, the triple point state characterized by continuous set of order parameters appears at zero external electric and magnetic fields and the tricritical points appear under external fields.
Near-room-temperature magnetoelectric coupling engineered through inversion-breaking tilts in a bulk perovskite polytype
University of Warwick（华威大学）；Luxembourg Institute of Science and Technology（卢森堡科学技术研究所）；Rutherford Appleton Laboratory（鲁瑟福阿普尔顿实验室）；Durham University（杜伦大学）
Magnetic field driven enhanced ferroelectric switching in self-grown ferroelectric-ferromagnetic composite in the BiFeO3-BaTiO3 multiferroic alloy system
多年来，人们试图弥补多铁性BiFeO 3体相态的固有弱点，如高漏电流和铁磁相关性的缺乏，并通过与其他钙钛矿形成固溶体来利用其磁电势。近几年的研究表明，BiFeO_3与BaTiO_3的合金化，无论有无添加剂，都可以诱导铁电和铁磁开关。虽然从技术应用的角度来看，这两种铁性序的共存是令人鼓舞的，但该系统中铁磁性的起源仍然难以捉摸。在这里，我们合成了这样的组合物，并进行了详细的结构分析，采用磁性分离的粉末颗粒。我们发现，铁磁性的起源在于自发沉淀的一个小的（~ 1wt%）钡六角铁氧体（BaFe 9 O 19）相，通常未检测到在常规的X射线衍射研究从整个标本的粉末取样。我们还表明，尽管微不足道的分数的亚铁磁相，这种自生长的复合材料表现出显着增强的铁电开关在外部磁场的存在下。我们得到了一个直流磁电耦合~ 9 × 10-8 s/m，这是一个值，这是已报道的层状铁电/铁磁层压板和双层薄膜铁电-铁磁hetrostructures。我们的研究表明，合理的大磁电耦合是可实现的，在简单的0-3铁电-铁磁块状复合材料提供的合成策略的开发，诱导自发沉淀的铁磁相在小体积分数，以确保良好的绝缘行为的复合材料，从而开发。
