Weiquan Shao

Large E-field tunability of microwave ferromagnetic properties in Fe59.3Co28.0Hf12.7/PZN-PT multiferroic composites

Strong converse magnetoelectric coupling was observed in a multiferroic heterostructure of Fe59.3Co28.0Hf12.7 film on (011) cut lead zinc niobate-lead titanate (PZN-PT) slab, which exhibited a large electric field (E-field) tunability of microwave magnetic properties. With the increase of E-field from 0 to 6 kV/cm on PZN-PT, the ferromagnetic resonance (FMR) field Hr shifts downwards by 430.7 Oe along [011¯] direction and upwards by 492.9 Oe along [100] direction of the PZN-PT. Accordingly, the strong magnetoelectric coupling led to a significantly enhanced self-biased FMR frequency from 4.2 to 7.9u2009GHz under zero bias magnetic field, and the magnetic damping constant α was decreased from 0.0260 to 0.0185 at the same time. These features demonstrate that this multiferroic laminate is promising in fabrication of E-field tunable microwave components.

Large E-field tunability of microwave ferromagnetic properties in Fe50Co50-Hf/lead zinc niobate–lead titanate multiferroic laminates

Fe50Co50-Hf films were deposited on the (011)-cut single crystal lead zinc niobate–lead titanate (PZN-PT) substrates by a composition gradient sputtering (CGS) method. Strong converse magnetoelectric (ME) coupling was observed in the multiferroic laminates of CGS Fe50Co50-Hf/PZN-PT, which exhibited a large electric field (E-field) tunability of microwave magnetic properties. With the increase of E-field strength from 0 to 8u2009kV/cm, the ferromagnetic resonance (FMR) fields Hr shifted upwards by 270.2u2009Oe and downwards by 237.7u2009Oe along hard axis and easy axis directions, being equivalent to 33.8 and 29.7u2009Oeu2009cm/kV, respectively. Accordingly, the self-biased ferromagnetic resonance frequency fFMR significantly enhanced from 4.0 to 6.5u2009GHz with an increment of ΔfFMRu2009=u20092.5u2009GHz under a zero-bias magnetic field, and the magnetic damping constant α decreases from 0.0280 to 0.0185. The strong ME coupling between CGS Fe50Co50-Hf film and PZN-PT substrate not only enhanced the fFMR but also reduced the magnetic loss a...

Large E-field tunability of magnetic anisotropy and ferromagnetic resonance frequency of co-sputtered Fe50Co50-B film

Fe27.45Co30.19B42.36 (referred to as FeCoB) films with 100u2009nm in thickness were co-sputtered on (011)-cut lead zinc niobate-lead titanate (PZN-PT) single crystal substrate under RF powers of 80u2009W for Fe50Co50 target and 120u2009W for B target, respectively. The anisotropy field HK of the FeCoB/PZN-PT multiferroic composite is increased by more than 10 times, from 56 to 663u2009Oe under the E-field from 0 to 7u2009kV/cm due to the strong magnetoelectric coupling, corresponding to a large tunability of HK of 86.7u2009Oe cm/kV. At the same time, the self-bias ferromagnetic resonance frequency fFMR is dramatically shifted upwards by an electric field from 2.57 to 9.02u2009GHz with an increment of 6.45u2009GHz, corresponding to E-field tunablity of fFMR 921.4u2009MHz.cm/kV. These features demonstrate that FeCoB/PZN-PT multiferroic laminates prepared under an integrated circuits process are promising in fabrication of E-field tunable monolithic microwave integrated circuits (MMIC) devices and their components.

Stress competition and vortex magnetic anisotropy in FeCoAlO high-frequency soft magnetic films with gradient Al-O contents

A vortex magnetic anisotropy (VMA) was formed via the competition of residual stresses between radial and tangential directions in the FeCoAlO soft magnetic films (SMFs), prepared by a composition gradient sputtering (CGS) method. The VMA of the magnetic films gives rise to a rotating excitation direction of the ferromagnetic resonance. As a results, the as-deposited FeCoAlO films exhibit good high-frequency ferromagnetic properties with high permeability about 100, cut-off frequency over 2 GHz, and Qm factor over 50 along its individual excitation direction. These SMFs with the VMA are promising in the integration with the circular spiral inductors due to the geometrical match between the excitation direction of the SMFs and the circular inductor lines.

Preparation of dense nanostructured titania ceramic using two step sintering

Abstract TiO2 ceramic was sintered by two types of processes: a conventional isothermal sintering and a two step sintering. A full densification without notable grain growth was achieved when the specimen was first heated to a higher temperature (T1=1300°C) and then cooled immediately for a long treatment at a lower temperature (T2=1000°C). Nanostructured TiO2 ceramics with a grain size of 110 nm and relative density 97% has been prepared using a two step sintering procedure. The results show that it is possibe to prepare dense and fine size grain nanostructured titania ceramics under an optimum sintering condition. The two step sintering method can successfully suppress the accelerated grain growth that usually occurs during the final sintering stage and make it possible to apply titania ceremics as structure materials and tissue engineering materials.

Quasi magnetic isotropy and microwave performance of FeCoB multilayer laminated by uniaxial anisotropic layers

A Fe0.7Co0.3-B multilayer was laminated by three Fe0.7Co0.3-B ferromagnetic sublayers prepared by composition gradient sputtering. Three Fe0.7Co0.3-B ferromagnetic sublayers have their individual directions of uniaxial magnetic anisotropy, and the easy magnetic axis of neighboring sublayer successively rotates 60° in the film plane. It is exciting that a quasi magnetic isotropy was achieved in the designed multilayer with a quasi-isotropic hysteresis loop and quasi-isotorpic ferromagnetic resonance around 3.7u2009GHz. This omnidirectional multilayer is promising for the application in inductors since the 100% hard-axis excitation is achieved for any shaped inductors.

Construction and validation of master sintering curve for TiO2 for pressureless sintering

Abstract One of the ultimate objectives for sintering research is to predict densification results under different thermal profiles for a given processing method. This paper studies the construction and validation of the master sintering curve (MSC) for rutile TiO2 for pressureless sintering. The MSC was constructed using dilatometry data at two heating rates and was then validated using isothermal holds at three different temperatures. The scanning electron microscopy (SEM) observation shows that the partially sintered samples have the same density under different heating procedures, which demonstrates that the assumptions of the model are reliable. The concept of the MSC could be used to predict the sintering shrinkage and final density and calculate the activation energy. A value of 105 kJ mol-1 for TiO2 was obtained. The MSC could be applied to predict the sintering profile to prepare ceramics with required density and a minimum of grain growth.

Electric field tunability of microwave soft magnetic properties of Co2FeAl Heusler alloy film

Co2FeAl Heusler alloy film with 100u2009nm in thickness was sputtered on (011)-cut lead zinc niobate-lead titanate (PZN-PT) single crystal slabs. It was revealed that this multiferroic laminate shows very large electric field (E-field) tunability of microwave soft magnetic properties. With the increase of electric field from 0 to 8u2009kV/cm on PZN-PT, the anisotropy field, HK, of the Co2FeAl film along [100] direction of PZN-PT is dramatically enhanced from 65 to 570u2009Oe due to the strong magnetoelectric (ME) coupling between ferromagnetic Co2FeAl film and ferroelectric substrate. At the same time, the damping constant α of Co2FeAl film dramatically decreases from 0.20 to 0.029. As a result, a significantly shift of self-biased ferromagnetic resonance frequency, fFMR, from 1.86 to 6.68u2009GHz with increment of 3.6 times was obtained. These features demonstrate that Co2FeAl/PZN-PT multiferroic laminate is promising in fabrication of E-field tunable microwave components.

Apparent sintering activation energy for densification of nanosized TiO2 ceramic powders

Abstract TiO2 powder samples with an average particle size of 50 nm were sintered in air at 1200°C at different heating rates of 1, 3, 5 K min–1. The apparent sintering activation energy was determined from dilatometer shrinkage data using the Arrhenius theory. The results give an activation energy of 115 ± 10 kJ mol–1 for the present material, which is in good agreement with values reported in the literature. It is concluded that the constant rate of heating method can be used to measure activation energy.

Relationship of densification rate and relative density for submicron α-Al2O3 green compacts during low heating rate sintering

Abstract The sintering of α-Al2O3 powder compacts with the mean particle size of 350 nm has been investigated at constant heating rates of 0˙5–5°C min–1. Curves of the instantaneous relative density differences and the temperature for different heating rates were constructed, the changing trend of which was consistent with that of densification rate v. temperature. The correlation between densification rate and the relative density was also constructed from the beginning to the end of the sintering process. Maximum densification rates occur at the same relative density of ∼73% and are independent of heating rates. For samples with the same initial relative density, the logarithm of temperature derivative of the densification rate v. the relative density fits within a single, relatively narrow band.