Studies on Doped Complex Adaptive Magneto-Electric Manganites
|關鍵字:||複雜自適應物質;磁電多鐵性材料;complex adaptive matters;multiferroic materials|
This proposal is intended to extend our efforts and experiences gained from the extensive investigations on the emergent behaviors exhibited by the complex adaptive matters characterized by strongly-correlated electrons, in particular, in the perovskite oxides-related thin films over the past few years. We will utilize the existent PLD system and low-temperature physical properties measuring system to investigate emergent properties of the doped magneto-electric multiferroic systems. In particular, in regarding to the fact that current researches have been mainly focused on identifying the major interactions that lead to the coexistence of multiferroic phases, we think the following questions should be addressed, at least, equally importantly. The questions are: 「Is there a coupling between these interactions?」「If yes, what is the dominant coupling mechanism?」 These are all the fundamental questions centered to the understanding of these so-called 「complex adaptive matters」that needed to be answered. For instance, intuitively, ferroelectricity often originates from the off-center asymmetry induced by structure distortion of the lattice, whereas, magnetism is intimately related to the local spin structure. Why would these two seemingly irrelevant phases (or phenomena) coexist in the some particular materials? Is the coexistence of multiphases a result of competition or compromise between different interactions among different quasiparticles? Does the interplay between them can be somehow modulated by the external perturbations in a controllable way? Even more interestingly from the application point of view, in most of the current situations, the existent multiferroic materials appears to be incapable of providing enough interplay between the ferroelectricity and ferromagnetism (or anti-ferromagnetism) to put up viable functional devices. It is thus very important to find a way of tuning these effects. It will be a key to not only gain understanding on the physics behind the complex adaptive nature of these materilas but also to give rise devices with novel functionalities. There is a clue that these may all be accomplished. Inspired from the experience in studying the colossal magnetoresistive materials (which are also complex adaptive matters by definition), doping can play a key role in changing the interactions. In that case, the introduction of itinerant carriers by doping triggers the double-exchange interaction between local spin moments and, in turn, leads to a transition from paramagnetic insulator to ferromagnetic metal. Similar physics is expected to prevail in these multiferroics, as well. We intend, in the next three years, to combine the superior advantages of pulsed laser deposition technique in growing stoichiometric oxide films and achieving wide range doping and the experiences we had gained previously, to systematically investigate the physical properties of doped multiferroic systems, such as YMnO3, HoMnO3, TbMnO3. It is hoped that by finding a way of tuning the interactions that lead to various robust pahses existent in the system, the fundamental physics and possibly novel device functionalties can be sucessfuly explored.
|Appears in Collections:||Research Plans|