Chenglong Jia

Current-induced magnetic skyrmions oscillator

Spin transfer nano-oscillators (STNOs) are nanoscale devices which are promising candidates for on-chip microwave signal sources. For application purposes, they are expected to be nano-sized, to have broad working frequency, narrow spectral linewidth, high output power and low power consumption. In this paper, we demonstrate by micromagnetic simulation that magnetic skyrmions, topologically stable nanoscale magnetization configurations, can be excited into oscillation by a spin-polarized current. Thus, we propose a new kind of STNO using magnetic skyrmions. It is found that the working frequency of this oscillator can range from nearly 0 Hz to gigahertz. The linewidth can be smaller than 1 MHz. Furthermore, this device can work at a current density magnitude as small as 108 A m−2, and it is also expected to improve the output power. Our studies may contribute to the development of skyrmion-based microwave generators.

Piezoelectric control of magnetic anisotropy in the Ni0.46Zn0.54Fe2O4/Pb(Mg1/3Nb2/3)O3-PbTiO3 composite

A gate-controllable in-plane magnetic anisotropy with C2v symmetry was observed in a Ni0.46Zn0.54Fe2O4/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure. Detailed amplitude analysis reveals a linearly electric modulation in anisotropy energy that arises from a strain-mediated magnetoelectric coupling across the interface. In particular, an electrically-driven rotational in-plane magnetic easy axis and anisotropic-isotropic transition in NiZn ferrite film, respectively, enable possibilities for magnetization control in multiferroic devices.

Hydrothermal epitaxial growth and nonvolatile bipolar resistive switching behavior of LaFeO3-PbTiO3 films on Nb:SrTiO3(001) substrate

Epitaxial LaFeO3-PbTiO3 (LFPTO) thin films were hydrothermally grown on the Nb-SrTiO3 (100) (NSTO) substrates with a thickness about 250 nm. As fabricated Pt/LFPTO/NSTO/Pt devices exhibit reversible bipolar resistive switching behavior. The resistance ratios between high resistance state and low resistance state exceed three orders of magnitude, which can be maintained over 6 h without observable degradation. It indicates that the Pt/LFPTO/NSTO/Pt devices reveal excellent data retention and endurance characteristics. The resistive switching mechanism of the device could be attributed to the trap-controlled space-charge-limited current conduction which is controlled by the localized oxygen vacancies in the films. Furthermore, variation of Pt/LFPTO Schottky junction depletion thickness and barriers height modulated by oxygen vacancies at Pt/LFPTO interface was suggested to be responsible for the resistance switching behaviors of the devices.

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.

Polarization-induced resistive switching behaviors in complex oxide heterostructures

Complex oxide heterostructures are fabricated by growing La0.67Ca0.33MnO3 films on ferroelectric 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (011) single-crystal substrates. The nonvolatile or pulsed resistive switching behaviors induced by an electric field are achieved simultaneously. Further analyses indicate that the different resistive switching behaviors are resulted from co-control of piezostrain and polarization current effects. With decreasing in-plane read current from 0.1 mA to 0.001 mA, the polarization current effect gradually begins to play a more important role than the piezostrain effect. Consequently, the nonvolatile resistive switching behavior is converted to pulse resistive switching behavior. The results further enhance the application of complex oxides in multifunctional memory devices.

Temperature dependence of electric field tunable ferromagnetic resonance lineshape in multiferroic heterostructure

Herein, we experimentally investigate the effect of temperature on the electric field tunable ferromagnetic resonance (FMR) in a ferroelectric/ferromagnetic heterostructure, and demonstrate the tuning of abnormal change in FMR using the polarization of the ferroelectric layer above 200 K. The FMR was found to be almost unchanged under different electric field strength at 100 K owing to frozen polarization, which causes extremely weak magnetoelectric coupling. More interestingly, negative effective linewidth was observed when an electric field greater than 10 kV/cm was applied above 220 K. The simultaneous electrical control of magnetization and its damping via FMR based on linear magnetoelectric coupling are directly relevant to use of composite multiferroics for a wide range of devices.