Nian Xiang Sun
Katherine S. Ziemer, Philip E. Serafim
Date of Award
Doctor of Philosophy
Department or Academic Unit
College of Engineering, Department of Electrical and Computer Engineering
electrical engineering, materials science, magnetoelectric effect, magnetoresistance, multiferroics
Electrical and Computer Engineering
E-field tuning of magnetism has become an exciting new frontier due to its wide range of potential applications in information storage, sensors, and novel electrostatically tunable microwave magnetic devices such as filters, resonators, inductors and phase shifters. Multiferroic composites, consisting of separate ferromagnetic and ferroelectric phases, have been utilized to electrically control magnetic order through strain mediated ME coupling resulting from the inversed piezoelectric effect and piezomagnetic effect. In this work, attempts of electrically tuning magnetism were made in nano-composites multiferroics and laminate multiferroic heterostructures. Remarkable E-field control of magnetism in laminate heterostructures was demonstrated, showing a record high E-field induced magnetic anisotropy, towards to realizing large tunable microwave device and spintronic devices.
First, we attempt to demonstrate ME coupling in nano-composite multiferroics. One-dimensional multiferroic core(NiFe2O4) -shell( (Pb(Zr0.52Ti0.48)O3 ) nanowire was firstly prepared by combining a modified sol-gel process, electrochemical deposition, and subsequent oxidization in anodized nanoporous alumina membranes. Well-defined individual multiferroic core-shell nanowire with clear boundary can be self-assembled under a certain magnetic field and patterned on the template for ME measurement. However, E-field tuning of magnetism in nano-composites is challenge due the large current leakage caused by small resistivity of magnetic phase. In addition, 0-3 type of CoFe2O4/PZT nano-composite was synthesized by modified Sol-Gel process. The ME coupling was demonstrated through spontaneous electric polarization change as applying a magnetic field.
Second, Ni0.23Fe2.77O4(NFO)/PZT (lead zirconium tinatate), Ni0.26Zn0.1Fe2.63O4(NZFO)/ (011) cut PMN-PT, Zn0.1Fe2.9O4(ZFO)/ (011) cut PMN-PT, Fe3O4/PZT, Fe3O4/ (011) cut PMN-PT, and Fe3O4/ (011) cut PZN-PT (lead zinc niobate-lead titanate) were prepared by spin-spray process at a low temperature of 90 degree of celsius. Strong magnetoelectric coupling (ME) and giant microwave tunability were demonstrated by a electrostatic field induced magnetic anisotropic field change in these heterostructures. A high electrostatically tunable ferromagnesim resonance (FMR) field shfit up to 600 Oe, corresponding to a large microwave ME coefficient of 67 Oe cm/kV, was observed in Fe3O4/PMN-PT heterostructures. A record-high electrostatically tunable FMR field range of 860 Oe with the linewidth of 330~380 Oe was demonstrated in Fe3O4/PZN-PT heterostructure, corresponding to a ME coefficient of 108 Oe cm/kV. Static ME interaction was also investigated and a maximum electric field induced squareness ratio change of 40% was observed in Fe3O4/PZN-PT. In addition, a new concept that the external magnetic orientation and the electric field cooperate to determine microwave magnetic tunability was brought forth to significantly enhance the microwave tunable range up to 1450 Oe. These low temperature synthesized multiferroic heterostructures exhibiting giant electrostatically induced tunable magnetic resonance field at microwave frequenciues provide great opportunities for electrostatically tunable microwave multiferroic devices.
Third, E-field modulation of anisotropy magnetoresistance (AMR) was demonstrated in Ni80Fe20/PZN-PT heterostructure. Surface magnetoelastic effect induced strong magnetoelectric (ME) coupling was observed in 10 nm thick Ni80Fe20/PZN-PT, showing a E-field induced large magnetic anisotropy field of 150 Oe. A multiband tunable AMR device was proposed. Electric field dynamically modulating of magnetoresistance (MR) was also studied. This electric field tuning of magnetism in ultra-thin Ni80Fe20/PZN-PT provides great opportunities for electrostatic tunable microwave devices and spintronics.
Finally, E-field tuning of exchange coupling was studied in ferromagnetic/anti-ferromagnetic/ferroelectric (FM/AFM/FE) mulitferroic heterostructures. A dramatically E-field changing of exchange bias was achieved in FeMn/FeGaB/PZN-PT, evidenced by the shift of magnetic hysteresis loops. E-field switching of magnetization by 180o was also demonstrated without external maangetic bias field. This provides great potential application in tunable spintronic devices.
Liu, Ming, "E-eld tuning of magnetism in mulitferroic heterostructures" (2010). Electrical Engineering Dissertations. Paper 32. http://hdl.handle.net/2047/d20000948
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