Electric-Field Control Of Magnetism In Ferrite Films With Multi-magnetic Anisotropy

The development of electronic information technology has put forward high requirements for electronic devices. Electric field control of magnetism of magnetic materials and devices has highly potential applications in the field of ultra-high density magnetic recording, magnetic random access memory, magnetic-microwave devices etc. Thereby, more attentions are paid to it. However, reports about the electrical control of magnetic systems with more than one easy axes（including single crystal thin film and composite films） are very few, so the main content of this thesis is to study magnetic properties of ferrite single crystal film and composite film controlled by electric field by theoretical analysis and micro-magnetic simulatiaon. The specific following results are obtained:Electric-field control of magnetic properties of Fe₃O₄ single-crystal thin film on the PZN-PT piezoelectric single crystal substrate has been investigated in detail. When the electric field is not applied, the film exhibits typical four-fold in-plane magnetocrystalline anisotropy, while when the electric field strength is not less than 0.6 MV/m, the electric-field-induced uniaxil anisotropy plays a dominant role. The change of sign of electric field can induce a 90-degree rotation of the easy axis of uniaxil anisotropy.A detailed study of the electric field control of exchange spring effect in soft/hard magnetic composite films has been introduced in this content. There are three systems, including PZN-PT/Co₄₃Fe₄₃B₁₄/CFO, PZT/CFO/Fe₃O₄ and PZT/CFO/Fe₃O₄. The results show that the regulation of magnetism in PZN-PT/Co₄₃Fe₄₃B₁₄/CFO by electric field is the most obvious, which is related to the strong piezoelectric voltage coefficient of the piezoelectric phase and the strong magnetostriction coefficient of the magnetic phases. The applied negative electric field can result in a 90-degree angle between the two phase anisotropy axes, and the system exhibits the typical exchange spring behavior. The different thickness ratios between two phases also make significant impact on the electric-field control of switching field and nucleation field of the exchange-spring system. When such thickness ratio is moderate, the change of anisotropy constants of both phases under the external electric field is competing for affecting the magnetic properties of the composite films. In addition, when there is an acute angle between magnetic field and phase easy axis under negative electric field, the hysteresis loop shows step characteristics. In this case, the magnetization reversal must overcome two anisotropic energy barriers, which is expected to achieve poly-state information storage.