Jiajun Guo

Electric field control of magnetism in Ti/ZnO/Pt and Ti/ZnO/SRO devices

We report electric field induced magnetic switching behaviours of un-doped ZnO films grown on Pt and SrRuO3 (SRO) bottom electrodes. The coexistence of great resistive and magnetic switching was observed in both devices under an applied electric field, but the magnetic change is opposite in ZnO films grown on Pt and SRO electrodes. By fitting the current–voltage curves of the samples, we found that we could attribute the resistive switching behavior to filamentary conduction in the Ti/ZnO/Pt device and interfacial Schottky barrier effects in the Ti/ZnO/SRO device. The underlying mechanism for magnetic switching behavior of Ti/ZnO/Pt and Ti/ZnO/SRO devices is discussed based on their resistive switching mechanism. Our work suggests that the magnetic properties of un-doped ZnO films can be greatly altered by applying a small voltage.

Ultra-low voltage control of magnetic properties in amorphous MgO

We report ultra-low voltage controlled magnetic properties in an amorphous MgO (a-MgO) thin film. The intrinsic magnetization of MgO can be decreased by about 57.5% by the application of a positive bias voltage while increased by about 56.7% by a negative bias, at an ultralow voltage of just 0.2 V. More interestingly, this ultralow voltage also induces a strong magnetic anisotropy in the a-MgO film. Further analysis indicates that the migration of O2− ions under an electric field results in a change in the Mg/O ratio and the redistribution of Mg vacancies, thus leading to the change in the magnetic properties of the film. The control of room temperature magnetic properties at ultralow voltages may find applications in multifunctional memory and ultralow-power consumption spintronics.We report ultra-low voltage controlled magnetic properties in an amorphous MgO (a-MgO) thin film. The intrinsic magnetization of MgO can be decreased by about 57.5% by the application of a positive bias voltage while increased by about 56.7% by a negative bias, at an ultralow voltage of just 0.2 V. More interestingly, this ultralow voltage also induces a strong magnetic anisotropy in the a-MgO film. Further analysis indicates that the migration of O2− ions under an electric field results in a change in the Mg/O ratio and the redistribution of Mg vacancies, thus leading to the change in the magnetic properties of the film. The control of room temperature magnetic properties at ultralow voltages may find applications in multifunctional memory and ultralow-power consumption spintronics.

Microstructure related quantum conductance in Mn-doped ZnO resistive switching memory

The quantization of conductance in a Ti/ZnO:Mn/Pt resistive switching memory device is investigated in this study. The Mn-doped ZnO films are deposited by pulsed laser deposition at 400°C and post-annealed for 20 min. Observations show that the high crystallinity and fine microstructures in the ZnO:Mn film play an important role for the quantum conductance behavior.

Study on the oxygen vacancy redistribution and the mechanism of electrical manipulation of ferromagnetism in diluted magnetic oxides

Electrical manipulation of room temperature ferromagnetism (RTFM) has been observed in several kinds of transition metal doped diluted magnetic oxide films. We demonstrate using X-ray photoelectron spectroscopy that the redistribution of the oxygen vacancies in a film under an electric field plays a crucial role in the enhancement of the RTFM. Based on a detailed analysis of the X-ray photoelectron spectroscopy data for the oxygen vacancy distribution in different resistive states, a unified mechanism has been proposed. This work points out a new direction for improving the magnetic properties of these materials by controlling oxygen vacancies in the interior of the films.

Enhanced magnetic modulation in HfO2-based resistive memory with an Hf top electrode

Magnetic modulation in binary-oxide-based resistive random access memory (RRAM) shows promise for applications in future electronics. However, the small magnetization change and large operating voltage in undoped binary oxide films make its practical applications difficult. In this study, we investigated magnetic switching behaviors in RRAM devices based on HfO2 film utilizing either Ti or Hf as the top electrode (TE). Substantially enhanced magnetic modulation and reduced operating voltage of the HfO2 film is demonstrated in the device using an Hf TE. The saturation magnetization of the HfO2 film is more than four times larger in a low resistance state than in a high resistance state under a set/reset voltage of only 0.4/0.3 V. We propose that these results are related to two factors: the high standard Gibbs energy of oxide formation for metal Hf; and the dual ion diffusion of hafnium (originating from the Hf TE) and oxygen in the device. This work shows that selecting a suitable TE can result in enhanced capability for electrical control of magnetism in metal oxides.Magnetic modulation in binary-oxide-based resistive random access memory (RRAM) shows promise for applications in future electronics. However, the small magnetization change and large operating voltage in undoped binary oxide films make its practical applications difficult. In this study, we investigated magnetic switching behaviors in RRAM devices based on HfO2 film utilizing either Ti or Hf as the top electrode (TE). Substantially enhanced magnetic modulation and reduced operating voltage of the HfO2 film is demonstrated in the device using an Hf TE. The saturation magnetization of the HfO2 film is more than four times larger in a low resistance state than in a high resistance state under a set/reset voltage of only 0.4/0.3 V. We propose that these results are related to two factors: the high standard Gibbs energy of oxide formation for metal Hf; and the dual ion diffusion of hafnium (originating from the Hf TE) and oxygen in the device. This work shows that selecting a suitable TE can result in enhance...

One-step synthesis and structural quantitative analysis of La2/3Sr1/3MnO3/La1.4Sr1.6Mn2O7 composites

Abstract La 2/3 Sr 1/3 MnO 3 /La 1.4 Sr 1.6 Mn 2 O 7 composites with arbitrary weight percentage were prepared using a one-step solid-state reaction method. The experimental results demonstrated that addition of K 2 CO 3 during preparation favored the formation of the composites even though the K + ions were volatilized under the high temperatures of sintering. Full quantitative analysis with the Rietveld method showed that the content of La 1.4 Sr 1.6 Mn 2 O 7 phase decreased and the fraction of the La 2/3 Sr 1/3 MnO 3 phase increased as the amount of K 2 CO 3 was increased.