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The coexistence of electric polarization and magnetization in multiferroic materials provides great opportunities for realizing magnetoelectric (ME) coupling, including electric field control of magnetism, or vice versa, through a strain-mediated ME coupling in layered magnetic/ferroelectric multiferroic heterostructures. Strong ME coupling has been the enabling factor for different multiferroic devices, which, however, has been elusive, particularly at RF/microwave frequencies. In this paper, most recent progress on new integrated multiferroic devices for sensing RF and microwave electronics will be presented, including novel RF Nano-electro-mechanical systems ME resonators with picotesla sensitivity for dc magnetic fields and novel gigahertz magnetic and multiferroic integrated inductors with a wide operation frequency range of $0.3\sim 3$ GHz, a high quality factor close to 20, and a voltage tunable inductance of 50% $\sim 150$ %. At the same time, we will also demonstrate other tunable RF devices, including integrated non-reciprocal tunable bandpass filter with ultrawideband isolation more than 13 dB. These novel magnetics and multiferroic devices show great promise for applications, such as compact, lightweight, and power-efficient sensing, memory, RF, and microwave integrated electronics. [ABSTRACT FROM PUBLISHER]

An orthogonal biaxial magnetic anisotropy configuration was built in the FeCoAlO/PZN–PT multiferroic composite using two perpendicular uniaxial magnetic anisotropies (UMAs). One is stable and induced by composition gradient, and the other is electric field (E-field) dependent resulting from the magnetoelectric coupling between FeCoAlO ferromagnetic film and the PZN–PT ferroelectric substrate. As a result, the easy axis of a FeCoAlO soft magnetic film can be rotated nearly 90° by the E-field due to the competition between the two UMAs. The magnitude and direction of the ferromagnetic resonance frequency can be manipulated by E-field, and very high resonance frequency up to 9 GHz is achieved in this orthogonal biaxial multiferroic composite. [ABSTRACT FROM AUTHOR]

Perpendicular exchange bias (EB), which combines perpendicular magnetic anisotropy and ferromagnetic (FM)–anti‐ferromagnetic (AFM) exchange coupling, is extremely important in high‐density AFM spintronics. However, the effective modulation of EB remains challenging, since the alternant spins at the AFM/FM interface are strongly pinned by the AFM layer. Voltage tuning of EB through magnetoelectric coupling provides a potential way to achieve rapid magnetization switching in an energy‐efficient manner. Nevertheless, the interfacial strain mediation of perpendicular EB induced by E‐field remains unexplored. In this work, perpendicular EB nanostructure by room‐temperature fabrication process is obtained, and the voltage tunable perpendicular EB in Pt/IrMn/(Co/Pt)2/Ta/(011) Pb(Mg1/3Nb2/3)O3‐PbTiO3 multiferroic heterostructure is demonstrated. To enhance the voltage control effect on perpendicular EB, both strain‐mediated magnetoelectric coupling and ionic liquid gating method are further investigated in the thinned EB system with the structure of Pt/IrMn/Co/Pt/Ta. As a result, the voltage induced lattice distortion effectively transmits to the AFM/FM interface, while the charge accumulation and ion migrations in gating method generate a relatively large hysteresis loop offset that has not been observed before at room temperature. The voltage manipulation of perpendicular EB at room temperature provides new possibilities toward novel AFM devices and memories with great energy‐efficiency and ultrahigh density. [ABSTRACT FROM AUTHOR]

Strain-mediated magnetoelectric effect can be utilized as an energy-efficient approach for spin manipulation. However, over 90° magnetization rotation is still challenging in un-patterned magnetic films, as the piezo-strain driven by ferroelectric domain switching is generally uniaxial rather than unidirectional, which limits the developments of non-volatile magnetic memory and logic devices. Here we demonstrate the rotation of local magnetization with a large angle of 136° by applying strains with a shear component at a fixed magnetic field of 45 Oe in FeCoSiB/PMN-PT (011) multiferroic heterostructures, revealed by a vector-resolved quantitative magneto-optical Kerr effect (MOKE) microscopy. Phase-field simulations confirm that the approximate 140° rotation of magnetization vectors is a consequence of the shear strain associated with ferroelectric/ferroelastic switching of PMN-PT (011) substrates. The visualization of over 90° magnetization rotation induced by the strain with a shear component paves the way for deterministic magnetization switching that has important implications in the energy-efficient spintronic devices. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We report a continuously tunable resistive switching behavior in Pt/BiFeO3/Nb-doped SrTiO3 heterostructure for ferroelectric memristor application. The resistance of this memristor can be tuned up to 5 × 105% by applying voltage pulses at room temperature, which exhibits excellent retention and anti-fatigue characteristics. The observed memristive behavior is attributed to the modulation effect of the ferroelectric polarization reversal on the width of depletion region and the height of potential barrier of the p-n junction formed at the BiFeO3/Nb-doped SrTiO3 interface. [ABSTRACT FROM AUTHOR]

Abstract: The CoFe2O4 (CFO)/Bi3.15Nd0.85Ti3O12 (BNT) multiferroic composite coaxial nanotubes were prepared by a sol–gel template method. The morphologies of the coaxial nanotubes were characterized and the selected area electron diffraction patterns confirmed the coexistence of spinel CFO and perovskite BNT phase. The vibrating sample magnetometer measurements showed that the saturation magnetization and coercive field of the coaxial nanotubes were 1emu/g and 0.7kOe, respectively, which was contributed totally from the inner CFO nanotubes. The CFO/BNT coaxial nanotubes showed typical ferroelectric hysteresis loop, while the increased leakage current density is likely due to the high conductivity in the inner CFO nanotubes. Our study demonstrated that the CFO/BNT coaxial nanotubes were of both ferroelectric and magnetic features in nanoscale. [Copyright &y& Elsevier]

Amorphous FeBSiC thin films were deposited on PMN-PT (Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 )(001) single crystal substrate by DC magnetron sputtering. The effects of piezoelectric-poling-induced strain on the magnetic properties of the FeBSiC/PMN-PT heterostructures were investigated. Studies indicated that the non-linear strains in PMN-PT were induced by poling at different electric fields, with tensile strain for out-of-plane direction and compressive strain for in-plane direction, respectively. Moreover, the in-plane compressive strain increased the saturation magnetization of the FeBSiC thin film, while the out-of-plane tensile strain decreased it. These results could be attributed to the 109° ferroelastic domain switching at applied electric field, which induced large variation in magnetic anisotropy due to magnetoelectric coupling in the FeBSiC/PMN-PT heterostructures. This study demonstrates the non-volatile tuning of magnetism by non-linear strains of lattice induced by the piezoelectric-poling, which shows promising applications for energy efficient magnetoelectric devices. [ABSTRACT FROM AUTHOR]

The microstructures of Bi 0.85 Nd 0.15 FeO 3 ceramics were investigated by using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), convergent-beam electron diffraction (CBED) and X-ray energy dispersive spectrometry (EDS). The superstructure phase related to 1/4( hh 0) p and 1/4(00 l ) p diffraction spots were observed in the samples. It is found that the superstructure phase can co-exist with R 3 c phase in a single grain. The bright and dark field images accompanied with SAED patterns provided evidences of the superstructure phase dispersed into the matrix with R3c symmetry and evolution of the domain. The ferroelectric domain wall was observed according to the displacement of Fe 3+ ions respect to Bi 3+ sub-lattice in the ferroelectric R 3 c phase based on HRTEM observations. The space group Pnam of the superstructure was identified by combining SAED and CBED techniques. EDS measurement revealed that the concentration of Nd in the Pnam phase is higher than that in R 3 c phase. This might mean that the transition from R 3 c to Pnam structure is due to the inhomogeneous distribution of the Nd concentration and the weakened stereochemical activity of Bi 3+ lone electron pair, arisen from the increase in Nd content. [ABSTRACT FROM AUTHOR]