Nian X. Sun

Sandwich films: Properties of a new soft magnetic material

The development of advanced electromagnetic devices has been constrained by a lack of soft magnetic materials with a suitably high saturation magnetization (over 20 kilogauss) and a large permeability roll-off frequency (greater than 1 gigaherz). For example, magnetic hard-disk-drive technology is rapidly approaching the perceived superparamagnetic limit at which the stored bits become thermally unstable — disks with higher anisotropy are more stable but are not usable because magnetic write heads become saturated. Here we describe a new soft magnetic material with a saturation magnetization of 24 kilogauss and a large permeability of 1,000–1,400 in a wide frequency range of up to about 1.2 gigaherz. This new material promises to have wide application in devices such as magnetic recording heads and integrated inductors.

VOLTAGE CONTROL OF MAGNETISM IN MULTIFERROIC HETEROSTRUCTURES AND DEVICES

Multiferroic materials and devices have attracted intensified recent interests due to the demonstrated strong magnetoelectric (ME) coupling in new multiferroic materials and devices with unique functionalities and superior performance characteristics. Strong ME coupling has been demonstrated in a variety of multiferroic heterostructures, including bulk magnetic on ferro/piezoelectric multiferroic heterostructures, magnetic film on ferro/piezoelectric slab multiferroic heterostructures, thin film multiferroic heterostructures, etc. Different multiferroic devices have been demonstrated, which include magnetic sensors, energy harvesters, and voltage tunable multiferroic RF/microwave devices which are compact, lightweight, and power efficient. In this progress report, we cover the most recent progress on multiferroic heterostructures and devices with a focus on voltage tunable multiferroic heterostructures and devices with strong converse ME coupling. Recent progress on magnetic-field tunable RF/microwave dev...

Small Ultra-Wideband (UWB) Bandpass Filter With Notched Band

A compact ultra-wideband (UWB) bandpass filter (BPF) with notched band has been proposed and implemented in this letter. H-shaped slot is studied and adopted to tighten the coupling of inter-digital capacitor in order to improve the BPFs performance. Three pairs of tapered defected ground structures (DGS) are formed to assign their transmission zeros towards the out of band signal, thereby suppressing the spurious passband. Combining these two structures we obtain a small sized UWB BPF. Meander line slot is developed to reject the undesired wireless local-area network (WLAN) radio signals. An experimental UWB filter with notched band was fabricated with 35% less length as compared to an embedded open-circuited stub. The measured BPF insertion loss is less than 1.0 dB throughout the pass band of 2.8 to 10.8 GHz, the variation of group delay less than 0.20 ns in this band except for the notched band, and a wide stopband bandwidth with 20 dB attenuation up to at least 20.0 GHz.

Voltage Tuning of Ferromagnetic Resonance with Bistable Magnetization Switching in Energy‐Efficient Magnetoelectric Composites

Dual E- and H-field control of microwave performance with enhanced ferromagnetic resonance (FMR) tunability has been demonstrated in microwave composites FeGaB/PZN-PT(011). A voltage-impulse-induced non-volatile magnetization switching was also realized in this work, resulting from the hysteretic type of phase transition in PZN-PT(011) at high electric fields. The results provide a framework for developing lightweight, energy efficient, voltage-tunable RF/microwave devices.

Ba-hexaferrite films for next generation microwave devices (invited)

Next generation magnetic microwave devices require ferrite films to be thick (>300μm), self-biased (high remanent magnetization), and low loss in the microwave and millimeter wave bands. Here we examine recent advances in the processing of thick Ba-hexaferrite (M-type) films using pulsed laser deposition (PLD), liquid-phase epitaxy, and screen printing. These techniques are compared and contrasted as to their suitability for microwave materials processing and industrial production. Recent advances include the PLD growth of BaM on wide-band-gap semiconductor substrates and the development of thick, self-biased, low-loss BaM films by screen printing.

Soft high saturation magnetization (Fe/sub 0.7/Co/sub 0.3/)/sub 1-x/N/sub x/ thin films for inductive write heads

(Fe/sub 0.7/Co/sub 0.3/)/sub 1-x/N/sub x/ (or FeCoN) alloy single layers and FeCoN film sandwiched between two very thin (5 nm) permalloy layers have been synthesized by RF diode sputtering. The saturation magnetization of the as-deposited FeCoN single layers was found to be around 24.5 kG, the same as the pure Fe/sub 0.7/Co/sub 0.3/ alloy; and the minimum hard-axis coercivity was 5 Oe. In contrast, the sandwiched FeCoN films have a hard axis coercivity of 0.6 Oe, an excellent in-plane uniaxial anisotropy with an anisotropy field of 20 Oe. The optimized FeCoN films exhibit a BCC structure with a strong {110} fiber texture and the resistivity is 55 /spl mu//spl Omega//spl middot/cm. The combination of high saturation and low coercivity, makes the FeCoN films a very promising candidate for the write head materials for future magnetic recording.

Properties of a new soft magnetic material

Gavrilets replies — Tregenza et al. maintain that my models predictions run counter to the model of Parker and Partridge, but it is not straightforward to compare these two classes of model because of their inherent differences.

Self-Biased 215MHz Magnetoelectric NEMS Resonator for Ultra-Sensitive DC Magnetic Field Detection

High sensitivity magnetoelectric sensors with their electromechanical resonance frequencies < 200 kHz have been recently demonstrated using magnetostrictive/piezoelectric magnetoelectric heterostructures. In this work, we demonstrate a novel magnetoelectric nano-electromechanical systems (NEMS) resonator with an electromechanical resonance frequency of 215 MHz based on an AlN/(FeGaB/Al2O3) × 10 magnetoelectric heterostructure for detecting DC magnetic fields. This magnetoelectric NEMS resonator showed a high quality factor of 735, and strong magnetoelectric coupling with a large voltage tunable sensitivity. The admittance of the magnetoelectric NEMS resonator was very sensitive to DC magnetic fields at its electromechanical resonance, which led to a new detection mechanism for ultra-sensitive self-biased RF NEMS magnetoelectric sensor with a low limit of detection of DC magnetic fields of ~300 picoTelsa. The magnetic/piezoelectric heterostructure based RF NEMS magnetoelectric sensor is compact, power efficient and readily integrated with CMOS technology, which represents a new class of ultra-sensitive magnetometers for DC and low frequency AC magnetic fields.

Voltage‐Impulse‐Induced Non‐Volatile Ferroelastic Switching of Ferromagnetic Resonance for Reconfigurable Magnetoelectric Microwave Devices

A critical challenge in realizing magnetoelectrics based on reconfigurable microwave devices, which is the ability to switch between distinct ferromagnetic resonances (FMR) in a stable, reversible and energy efficient manner, has been addressed. In particular, a voltage-impulse-induced two-step ferroelastic switching pathway can be used to in situ manipulate the magnetic anisotropy and enable non-volatile FMR tuning in FeCoB/PMN-PT (011) multiferroic heterostructures.

Quantification of strain and charge co-mediated magnetoelectric coupling on ultra-thin Permalloy/PMN-PT interface

Strain and charge co-mediated magnetoelectric coupling are expected in ultra-thin ferromagnetic/ferroelectric multiferroic heterostructures, which could lead to significantly enhanced magnetoelectric coupling. It is however challenging to observe the combined strain charge mediated magnetoelectric coupling, and difficult in quantitatively distinguish these two magnetoelectric coupling mechanisms. We demonstrated in this work, the quantification of the coexistence of strain and surface charge mediated magnetoelectric coupling on ultra-thin Ni0.79Fe0.21/PMN-PT interface by using a Ni0.79Fe0.21/Cu/PMN-PT heterostructure with only strain-mediated magnetoelectric coupling as a control. The NiFe/PMN-PT heterostructure exhibited a high voltage induced effective magnetic field change of 375 Oe enhanced by the surface charge at the PMN-PT interface. Without the enhancement of the charge-mediated magnetoelectric effect by inserting a Cu layer at the PMN-PT interface, the electric field modification of effective magnetic field was 202 Oe. By distinguishing the magnetoelectric coupling mechanisms, a pure surface charge modification of magnetism shows a strong correlation to polarization of PMN-PT. A non-volatile effective magnetic field change of 104 Oe was observed at zero electric field originates from the different remnant polarization state of PMN-PT. The strain and charge co-mediated magnetoelectric coupling in ultra-thin magnetic/ferroelectric heterostructures could lead to power efficient and non-volatile magnetoelectric devices with enhanced magnetoelectric coupling.