Zn~(2+)、Sn~(4+)共取代对YIG铁氧体性能的影响

该文通过1 400℃固相烧结制备出Zn2+和Sn4+共取代的Y3Fe5-2xZnxSnxO12(x=0~0.35)铁氧体材料,详细研究了离子取代量对钇铁石榴石铁氧体微观结构及磁性能的影响。研究表明,Zn2+、Sn4+都进入了钇铁石榴石铁氧体的晶格中。随着离子取代量的增加,钇铁石榴石铁氧体的密度与饱和磁化强度先增大后减小;其磁损耗则先减小后增大,在x=0.25时磁损耗取得最小值。该研究进一步说明了Zn2+和Sn4+取代在一定范围内可有效降低材料的磁损耗及控制材料的饱和磁化强度。     

Tunable Optical Mode Ferromagnetic Resonance in FeCoB/Ru/FeCoB Synthetic Antiferromagnetic Trilayers under Uniaxial Magnetic Anisotropy

Ferromagnetic resonance (FMR) is one of the most important characteristics of soft magnetic materials, which practically sets the maximum operation speed of these materials. There are two FMR modes in exchange coupled ferromagnet/nonmagnet/ferromagnet sandwich films. The acoustic mode has relatively lower frequency and is widely used in radio‐frequency/microwave devices, while the optical mode is largely neglected due to its tiny permeability even though it supports much higher frequency. Here, a realistic method is reported to enhance the permeability in the optical mode to an applicable level. FeCoB/Ru/FeCoB trilayers are carefully engineered with both uniaxial magnetic anisotropy and antiferromagnetic interlayer exchange coupling. This special magnetic structure exhibits a high optical mode frequency up to 11.28 GHz and a maximum permeability of 200 at resonance. An abnormally low inverse switch field (<200 Oe, less than 1/5 of the single layer) is observed which can effectively switch the system from optical mode with higher frequency into acoustic mode with lower frequency. The optical mode frequency and inverse switch field can be controlled by tailoring the interlayer coupling strengths and the uniaxial anisotropy fields, respectively. The tunable optical mode resonance thus can increase operation frequency while reduce operation field overhead in FMR based devices.     

Ca~(2+)、Zr~(4+)共替代对YAlIG铁氧体性能的影响

采用固相烧结法制备旋磁铁氧体材料Y_(3-x)Ca_xAl_(0.33)Fe_(4.6-x)Zr_xMn_(0.02)O_(12)(摩尔分数x=0、0.2、0.25、0.3、0.35)。详细研究了Ca~(2+)、Zr~(4+)共替代对钇铝石榴石(YalIG)铁氧体性能的影响。研究表明,Ca~(2+)、Zr~(4+)替代对YAlIG铁氧体的介电常数影响微弱。随着替代量x的增加,YAlIG的饱和磁化强度起初呈上升趋势,但当替代量过多时,会使材料中产生另相,反而降低材料的饱和磁化强度(4πMs)。适量Ca~(2+)、Zr~(4+)共替代会明显降低YAlIG材料的铁磁共振线宽,随替代量x的增加,YAlIG材料的铁磁共振线宽(ΔH)先下降后上升,在无另相产生前的最大替代量x=0.3时,材料ΔH获得最小值。     

E‐Field Control of Exchange Bias and Deterministic Magnetization Switching in AFM/FM/FE Multiferroic Heterostructures

The coexistence of electrical polarization and magnetization in multiferroic materials provides great opportunities for novel information storage systems. In particular, magnetoelectric (ME) effect can be realized in multi­ferroic composites consisting of both ferromagnetic and ferroelectric phases through a strain mediated interaction, which offers the possibility of electric field (E‐field) manipulation of magnetic properties or vice versa, and enables novel multiferroic devices such as magnetoelectric random access memories (MERAMs). These MERAMs combine the advantages of FeRAMs (ferroelectric random access memories) and MRAMs (magnetic random access memories), which are non‐volatile magnetic bits switchable by electric field (E‐field). However, it has been challenging to realize 180° deterministic switching of magnetization by E‐field, on which most magnetic memories are based. Here we show E‐field modulating exchange bias and for the first time realization of near 180° dynamic magnetization switching at room temperature in novel AFM (antiferromagnetic)/FM (ferromagnetic)/FE (ferroelectric) multiferroic heterostructures of FeMn/Ni₈₀Fe₂₀/FeGaB/PZN‐PT (lead zinc niobate–lead titanate). Through competition between the E‐field induced uniaxial anisotropy and unidirectional anisotropy, large E‐field‐induced exchange bias field‐shift up to $ {{{\Delta H_{ex}}}\over{{H_{ex}}}} = 218\%$ and near 180° deterministic magnetization switching were demonstrated in the exchange‐coupled multiferroic system of FeMn/Ni₈₀Fe₂₀/FeGaB/PZN‐PT. This E‐field tunable exchange bias and near 180° deterministic magnetization switching at room temperature in AFM/FM/FE multiferroic heterostructures paves a new way for MERAMs and other memory technologies.