Magnetoelectric Properties Of Hexaferrite And Related Devices

The cross coupling between electric polarization and magnetization in multiferroic materials provides a great potential for creating next-generation memory devices.The spin-induced multiferroics is the hot topic in the area of condensed matter physics,where novel physical mechanisms have been found.From the viewpoint of application,people expect to use the multiferroics as the media for information storge to realize electric-write-magnetic-read operation.which enable the development of low power spintronic devices.Recording data by magnetism has a high reading speed but low writing speed,while ferroelectric memory has a high writing speed but a complex reading structure.By using multiferroics materials,we can combine these two advantages together to develop a nonvolatile memory device with high energy efficiency.Hexaferrites with fruitful physical properity is potential in application.The thesis cosists of Y-type hexaferrite and Z-type hexaferrite.The main results are summarized as follows.1 We report the new world records of direct magnetoelectric coefficient and converse magnetoelectric cofficient in Y type hexaferrites Ba_0.4Sr_1.6Mg₂Fe₁₂O₂₂,33000 ps/m and32000 ps/m,respectively.Magnetic measurements and neutron diffraction were performed in Sr systemically doped Ba₂Mg₂Fe₁₂O₂₂.We find that replacing Ba by Sr can effectively tune the magnetic structure and the superexchange interaction of Fe-O-Fe,which can induce the giant magnetoelectric coefficients.2 We find a electric field controlled exchange bias like effect in Ba_0.4Sr_1.6Mg₂Fe₁₂O₂₂.The magnetic hysteresis loop can shif by applying electric field and the bias field show a linear relationship with the electric field.The theoretical analysis find the bias effect may come from electrostatic energy.3 We investigate the the nonvolatile memory based on single phase multiferroic Z type heaxaferrite Sr₃Co₂Fe₂₄O₄₁ and Y type hexaferrite Ba_1.1Sr_0.9Co₂Fe₁₁AlO₂₂.We use the pluse electric field to write the nonvolatile binary information and obtain the“0”,“1”by reading the magnetitude of magnetoelectric coefficient.This is the first work to use single phase multiferroic material as media to store information at room temperature,which pave the way to the application of spin induced single phase multiferroic.