Research articles
Ionic liquid gating control of magnetism of a Co film

https://doi.org/10.1016/j.jmmm.2020.167261Get rights and content

Highlights

  • Ionic-liquid-gating modulates the saturation magnetization of a Co film.

  • The gated states are nonvolatile and stable. The gating processes are reversible.

  • The modulation of the ferromagnetism may be related with the motions of oxygen ions.

Abstract

Ionic liquid gating has emerged as an attractive means of manipulating the magnetic properties of materials. Here, we report ionic liquid gating modulating the ferromagnetism of a Co film. A weak and strong saturation magnetization can be reversibly obtained by applying a negative voltage and a positive one, respectively. The modulation may be related with the oxidization and reduction of Co. Negative (or positive) gating voltages drive the oxygen ions to inject into (or extract from) Co layer of the sample, which oxidizes (or reduces) Co. These gating processes are reversible. Moreover, the magnetism of the gated states is considerably stable. It is a significant step towards designing low-power electric-controlling magnetic devices in future.

Introduction

The control of magnetism and spin phenomena in information technology has been intensely pursued during the past few decades [1], [2]. Although a magnetic field is the usual means to switch magnetization of magnetic materials once they have been prepared, employing a non-magnetic means to switch and modulate magnetism is requisite taking ultra-small dimension and low energy consumption into account [3], [4], [5]. Among various means such as electrical, magnetic, optical and heating etc., electrical control of the properties of materials is highly desirable toward fast, compact, low power dissipation and light weighted devices for fundamental science and emerging applications [6], [7], [8]. Electrical control of the magnetism of the materials may be related with carrier modulation, strain effect, and electrochemical effect etc [1], [9]. In recent years, the electrochemical effect or the redox reaction is widely observed in systems with an ionic liquid (IL) [10], [11] or a high oxygen mobility material as GdOx [12], [13] used as a dielectric layer. In fact, the application of the ILs in the syntheisis of the nanocomposites [14], and electrochemical devices such as capacitors [15], batteries [16], and photocatalysis [17] etc has attracted much attention due to their various advantages, such as high thermal and chemical stability, non-volatility, nontoxicity, etc [11]. In recent years, ILs are particularly promising as gate dielectric materials of field-effect transistors and related devices to manipulate the properties of the materials owing to their large capacitance and large electrochemical window [6], [11], [18], [19], [20], [21]. Up to now, ionic liquid gating (ILG) on functional materials has already demonstrated its unique capability of exploring various exotic properties in many material systems, such as the insulator-metal transition, superconductivity, and magnetism etc [6], [18], [19], [20], [21], [22], [23], [24].

For modulating magnetism, ferromagnetic semiconductors have been most intensively investigated because their ferromagnetic properties are the function of carrier concentration [25]. Later, electric field controls of magnetization properties, magnetic anisotropy etc. have been demonstrated in the ferromagnetic metal materials [26], [27]. In this work, we chose a common ferromagnetic Co film and a typical, well-studied IL of N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis-trifluoromethylsulfonyl-imide (DEME-TFSI) with a high specific capacitance, a large electrochemical window (about ±3 V) and a high gating field at a moderate gating voltage (VG) [28], [29], [30] as the magnetic layer and the gating dielectric layer, respectively, designed an ILG device, and investigated the influence of gating parameters including VG and gating time on the magnetic properties of the Co films. It is found that magnetization of the Co film can be dramatically modulated, and a nearly ON-OFF magnetization of the Co film is realized by optimizing gating parameters. And the related mechanism was analyzed. These results will be useful for the devices based on electrical controlled magnetic systems.

Section snippets

Experimental details

A Ta(2 nm)/Pt(5 nm)/Co(0.6 nm)/Ta(2 nm) film was deposited on a thermal oxidized Si/SiO2 substrates by magnetron sputtering at room temperature (RT). The IL chosen for our experiment was commercial, as-received DEME-TFSI with theoretical water content of 100 ppm by mass. No systematic attempt was made to optimize the choice of IL. Usually a 3.5 mm × 4 mm sample was used for ILG experiments. Firstly, the sample was pasted on the chip. A layer of aluminum foil was set up above the sample and the

Results and discussion

Fig. 1(a) shows magnetic hysteresis loops of the pristine film when the magnetic field is applied in the in-plane and out-of-plane orientation at 300 K. No clear perpendicular magnetic anisotropy is observed. Fig. 1(b) shows the schematic of the ILG device structure. The device consists of a gate electrode, the IL of DEME-TFSI and the Ta(2 nm)/Pt(5 nm)/Co(0.6 nm)/Ta(2 nm) film. The modulation of magnetism of the Co layer by the ILG is as presented in Fig. 2 and 4.

Next, we investigate the effect

Conclusions

In summary, electric-controlling magnetism at room temperature is always a significant step towards realizing future low-power magnetic applications. In this work, it is achieved that the motions of O2− driven by IL gating effectively modulates the Ms of a Co film. A negative voltage drives the oxygen ions injecting into Co layer of the sample, which oxidizes Co to the Co oxide, resulting in the switching from the strong magnetization to weak one. Subsequently, applying a positive voltage on it

CRediT authorship contribution statement

Jie Yang: Investigation, Formal analysis, Writing - original draft. Xiaoxia Wang: Investigation, Formal analysis. Xiaoxiong Jia: Resources, Formal analysis. Yingmei Zhang: Formal analysis. Xiaoli Li: Conceptualization, Writing - review & editing, Supervision, Funding acquisition. Zhiyong Quan: Supervision, Funding acquisition. Zhongming Zeng: Writing - review & editing. Xiaohong Xu: Supervision, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Science Foundation of China (Grant Nos. 61306109, 61434002, 51571136, 11611540333), the Natural Science Foundation of Shanxi Province (201901D111282), the Project of Returness Scholarship of Shanxi Province (Grant No. 2014-044), and the Fund Program for the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province (Grant No. [2014]779).

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