Cai Zhou

Piezoelectric control of magnetic dynamics in Co/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure

A microstrip method with vector network analyzer was used to investigate electric field control of magnetic dynamic properties in Co/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure at room temperature. Under external electric field, the natural resonance frequency and permeability of the Co film were found to modulate between 1.8–2.8 GHz and 50–150, respectively. In addition, the in-plane uniaxial magnetic anisotropy field can also be electrically tuned from 54 to 170 Oe, while the ferromagnetic resonance field was substantially enhanced about 350 Oe as well. Such an improvement of magnetic anisotropy is desirable for effectively electric control of resonance frequency and permeability in low energy microwave devices.

A non-volatile four-state magnetic memory in a Co/(011)Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure

A non-volatile four-state magnetic memory is achieved in a Co/(011)Pb(Mg1/3Nb2/3)O-3-PbTiO3 heterostructure. The in-plane magnetization of ferromagnetic Co film in the heterostructure can be controlled both electrically and magnetically. Electric field mediated magnetism is caused by piezostrain effect, which displays a stable non-volatile remnant magnetization vs electric field looplike behavior. In-plane strain-electric field (S-E) behavior under different temperatures reveals a nonvolatile strain switching effect, which is responsible for the non-volatile remnant magnetization switching through piezostrain mediated magnetoelectric effect. Further investigations on temperature dependence of S-E behavior suggest that the absent of the second non-180 degrees domain switching may be responsible for the asymmetry in strain curves that causes the non-volatile strain switching, and therefore causes the non-volatile remanent magnetization switching, which is crucial for the four-state magnetoelectric memory

Stripe domain and enhanced resonance frequency in ferrite doped FeNi films

Stripe domain (SD) structures of FeNi films were controlled by doping different concentrations of ferrite. With increasing concentration of doped ferrite, SD width decreases, which indicated that perpendicular magnetic anisotropy (H⊥) increases. SD disappears and bubble-like features are observed with doping ferrite at 32% due to large H⊥. The origin for the enhancement of H⊥ is exchange coupling between ferrimagnet and ferromagnet. Moreover, different doping concentrations of ferrite realize an increase of resonant frequency from 1.3 to 2.3 GHz. (Some figures may appear in colour only in the online journal)

Lateral electric-field-driven non-volatile four-state memory in multiferroic heterostructures

A non-volatile four-state memory is formed using an in-plane side-polarization configuration in a Co/(011) Pb(Mg1/3Nb2/3)O3-PbTiO3 (Co/PMN-PT) heterostructure. The resistivity vs. electric field behavior shows a change from volatile butterfly to looplike to non-volatile butterfly characteristics when the temperature decreases from 290 K to 83 K under an electric field of 10 kV/cm and then increases back to 290 K; this behavior is attributed to the strain-mediated magnetoelectric effect. In addition, the in-plane resistivity of Co film, which was measured using the four-probe technique, can be controlled both electrically and magnetically. Specifically, a non-volatile resistivity is gained by the application of electric field pulses. Additionally, a four-state memory is obtained by co-mediation of the magnetic field and electric field pulses, compared with the two different states achieved under the application of the electric field only, which indicates that our results are highly important for multi-stat...

Piezostrain tuning non-volatile 90 degrees magnetic easy axis rotation in Co2FeAl Heusler alloy film grown on Pb(Mg1/3Nb2/3) O-3-PbTiO3 heterostructures

Non-volatile electric field-based control of magnetic anisotropy in Co2FeAl/Pb(Mg1/3Nb2/3) O-3-PbTiO3 (CFA/PMN-PT) heterostructures is investigated at room temperature. The remnant magnetization response under different electric fields shows a asymmetric butterfly-like behavior; specifically, this behavior is consistent with the asymmetric butterfly-like piezostrain versus applied electric field curve. Thus electric field-induced non-volatile 90 degrees magnetic easy axis rotation can be attributed to the piezostrain effect. Further, the result measured by rotating-angle ferromagnetic resonance demonstrates piezostrain-mediated non-volatile 90 degrees magnetic easy axis rotation at the initial state and the two remnant polarization states after application of the poling fields of 10 and -10 kV cm(-1) turned off. The angular dependence of magnetic damping also indicates a 90 degrees phase shift at the above mentioned three different states. Additionally, the piezostrain-mediated non-volatile stable magnetization reversal in the two directions of easy and hard magnetization axes are observed under positive and negative pulsed electric fields, which can be used to improve the performance of low-loss multiple-state memory devices.

Electric field induced natural resonance and magnetic damping in FeCo/ Pb (Mg1/3Nb2/3) O3-PbTiO3 heterostructures

We demonstrated that magnetic damping and natural resonance frequency could be modulated by the electric field in an FeCo layer on Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) heterostructures by the microstrip method with a vector network analyzer. Strain mediated natural resonance increased from 0.8 to 2 GHz with increasing the electric field from 0 to 12.5 kV cm−1. Furthermore, the magnetic damping factor increased from 0.008 to 0.225, which resulted from magnetization precession under a microwave field and interface charge mediated spin current due to the spin screening effect. The results were also validated by the measurements of ferromagnetic resonance, which was also clear from analysis of the intrinsic and extrinsic contributions to the magnetic damping. In addition, in-plane uniaxial static magnetic anisotropy field was also modulated from 8 to 200 Oe with a different electric field.

Enhancement of rotatable anisotropy in ferrite doped FeNi thin film with oblique sputtering

Rotatable anisotropy of stripe domain (SD) was investigated in a ferrite doped FeNi thin film with different oblique angles. Rotation of SD under an in-plane magnetic field was observed by magnetic force microscopy, suggesting the existence of rotatable anisotropy. A rotatable anisotropy field Hrot was derived from the fitting curves of the in-plane resonance field versus the angle between the orientation of easy axis and applied field. As the oblique angle increases, an increase of Hrot from 305 Oe to 468 Oe was observed and the perpendicular anisotropy increased as well, indicating a correlation between rotatable anisotropy and perpendicular anisotropy.

Electric field tuning resistance switching behavior of SrRuO3/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructures at various temperatures

The resistance switching behavior induced by in-plane read current in SrRuO3/Pb(Mg1/3Nb2/3) O-3-PbTiO3 heterostructures is investigated at different temperatures. With decreasing in-plane read current from 10 mA to 0.01 mA, the symmetrical butterfly-like shape of resistance is gradually converted to an antisymmetrical shape at different temperatures, which is resulted from the enhancement of polarization current effect. Specifically, non-volatile resistance behaviors induced by asymmetric bipolar sweeping of electric field and pulsed electric field are achieved at different temperatures. Our results suggests resistance switching behavior dependence of in-plane read current, which is crucial for further application of complex oxide magnetoelectric and spintronic devices.

Tuning magnetic anisotropy and the damping constant using substrate-induced strain in a FeCo/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure

To investigate how substrate-induced strain affects the magnetic anisotropy and damping constant, FeCo films were deposited onto Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) (0 1 1)-orientated substrates by RF-magnetron sputtering. Interestingly, as the strain, which is controlled by an applied electric field, increases, the magnetic anisotropy is enhanced while the damping constant decreases sharply. The angular dependence of coercive force and magnetoelastic energy were obtained to analyze the mechanism of magnetization reversal under strain modulation. The nonvolatile strain-modulation was demonstrated by the application of different pulsed electric fields. The reversible magnetization processes and low magnetic damping constant can be modulated by the substrate-induced strain, which can contribute to the realization of low-loss strain-mediated spin-transfer-torque based magnetic devices.

Electric Field Tuning Non-volatile Magnetism in Half-Metallic Alloys Co 2 FeAl/Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 Heterostructure

We reported the non-volatile electric field-mediated magnetic properties in the half-metallic Heusler alloy Co2FeAl/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure at room temperature. The remanent magnetization with different applied electric field along [100] and [01-1] directions was achieved, which showed the non-volatile remanent magnetization driven by an electric field. The two giant reversible and stable remanent magnetization states were obtained by applying pulsed electric field. This can be attributed to the piezostrain effect originating from the piezoelectric substrate, which can be used for magnetoelectric-based memory devices.