Electrical Modulation and Probing of Antiferromagnetism in Hybrid Multiferroic Heterostructures

TL;DR

Antiferromagnets offer ultrafast spin dynamics but no net magnetization, complicating detection and control. The study demonstrates all-electric control and probing of AFM order in heavy-metal/antiferromagnetic-insulator heterostructures on a piezoelectric PMN--PT substrate at room temperature, using Pt/NiO as the platform. AFM order is read by anomalous Hall effect and XMLD, and is non-volatilely modulated by ferroelectric polarization, yielding about a one-third change in the AHE signal; XMLD confirms the correlated AFM modulation. DFT results reveal an asymmetric response of exchange coupling to electron vs hole doping caused by the ferroelectric field effect, supporting a ferroelectric-field mechanism for AFM spintronic devices.

Abstract

The unique features of ultrafast spin dynamics and the absence of macroscopic magnetization in antiferromagnetic (AFM) materials provide a distinct route towards high-speed magnetic storage devices with low energy consumption and high integration density. However, these advantages also introduce challenges in probing and controlling AFM order, thereby restricting their practical applications. In this study, we demonstrate an all-electric control and probing of the AFM order in heavy metal (HM)/AFM insulator (AFMI) heterostructures on a ferroelectric substrate at room temperature (RT). The AFM order was detected by the anomalous Hall effect (AHE) and manipulated by the ferroelectric field effect as well as the piezoelectric effect in heterostructures of Pt/NiO/0.7Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$--0.3PbTiO$_{3}$ (PMN--PT). The non-volatile control of AFM order gives rise to a 33\% modulation of AHE, which is further evidenced by synchrotron-based X-ray magnetic linear dichroism (XMLD). Combined with the $in$-$situ$ piezoelectric response of AHE, we demonstrate that ferroelectric polarization contributes mainly to the control of the AFM order. Our results are expected to have broader implications for efficient spintronic devices.

Figures (15)

• Figure 1: The non-volatile electric-field control of AHE in HM/AFMI heterostructure. (a) The zoomed XRD pattern around (002) peak of 20 nm NiO thin film on PMN--PT substrate. (b) The schematic diagram of Hall bar device and transport property measurement set-up of Pt(3 nm)/NiO(3 u.c.)/PMN--PT. (c) The non-volatile electric field control of $R_\text{AHE}$ of Pt(3 nm)/NiO(3 u.c.)/PMN--PT for $P_{\uparrow}$ and $P_{\downarrow}$ states. The inset is schematic of polarization-electric field hysteresis loop. The blue and red dots represent the $P_{\uparrow}$ and $P_{\downarrow}$ states, respectively. (d) The temperature dependent $\sigma_\text{AHE}$ of Pt(3 nm)/NiO(3 u.c.)/PMN--PT for $P_{\uparrow}$ and $P_{\downarrow}$ states.
• Figure 2: The synchrotron-based XAS and XMLD results of Pt(3 nm)/NiO(3 u.c.)/PMN--PT heterostructure. (a) The schematic diagram of XAS measurements set-up. (b) The XAS results for $P_{\uparrow}$ and $P_{\downarrow}$ states with $\varphi=0^\circ$ and $\varphi=90^\circ$, as well as corresponding XMLD results. (c) The temperature-dependent XMLD results for $P_{\uparrow}$ state and $P_{\downarrow}$ state, respectively. The dashed line denotes the peak amplitude of XMLD signal.
• Figure 3: The piezoelectric effect on the AHE of Pt(3 nm)/NiO(3 u.c.)/PMN--PT heterostructure. (a) The schematic of measuring in-plane strain by strain gauge. (b) The monitored in-plane strain by sweeping out-of-plane electric field. The arrows indicate the sweeping direction of electric field. The blue and red dots represent the $P_{\uparrow}$ and $P_{\downarrow}$ states, respectively. (c) and (d), The electric-field dependent $R_\text{AHE}$ for heterostructure with (c) $P_{\uparrow}$ and (d) $P_{\uparrow}$ states, respectively. The red lines indicate the linear fitting.
• Figure 4: The DFT calculation of $J_\text{ex}$ controlled by ferroelectric field effect. (a) The schematic ferroelectric field effect on $J_\text{ex}$. For $P_{\uparrow}$ state, the positive bound charge on the NiO/PMN--PT interface induce electron doping into NiO layer, which possesses strong $J_\text{ex}$. For $P_{\downarrow}$ state, negative bound charge on the NiO/PMN--PT interface induce hole doping into NiO layer, which possesses weak $J_\text{ex}$. The yellow arrows are ferroelectric polarizations. The symbols "$+$" and "$-$" with circles denote positive or negative bound charge, while those without circles denote hole/electron doping. (b) the DFT calculated $J_\text{ex}$ as a function of the number of charge per u.c. ($N$) for electron or hole doping.
• Figure S1: The XRR raw data of (a) 18 nm NiO and (b) 49 nm Pt.