Ferroelectric Control of Spin Polarization (original) (raw)

Ferroelectric control of spin-transfer torque in multiferroic tunnel junctions

Physical Review B, 2015

Based on model calculations we predict electric-field control of the spin-transfer torque (STT) in magnetic tunnel junctions with ferroelectric barriers. We demonstrate that the bias dependence of the in-plane T and out-of-plane T ⊥ components of the STT can be dramatically modified by the ferroelectric polarization. In particular, the magnitude of the STT can be enhanced or suppressed by switching the polarization direction and in some cases the sign of STT can be toggled. The underlying mechanism is the combination of polarization-induced symmetry breaking and the interplay of the bias-induced and polarization-induced spin-dependent screening giving rise to a rich behavior of the electrostatic potential energy profile. These properties could lead to enhanced switching efficiency in STT-based devices and open a new avenue for applications of multiferroic devices.

Ferroelectric control of interface spin filtering in multiferroic tunnel junctions

2019

The electronic reconstruction occurring at oxide interfaces may be the source of interesting device concepts for future oxide electronics. Among oxide devices, multiferroic tunnel junctions are being actively investigated as they offer the possibility to modulate the junction current by independently controlling the switching of the magnetization of the electrodes and of the ferroelectric polarization of the barrier. In this Letter, we show that the spin reconstruction at the interfaces of a La_0.7Sr_0.3MnO_3/BaTiO_3/La_0.7Sr_0.3MnO_3 multiferroic tunnel junction is the origin of a spin filtering functionality that can be turned on and off by reversing the ferroelectric polarization. The ferroelectrically controlled interface spin filter enables a giant electrical modulation of the tunneling magnetoresistance between values of 10% and 1000%, which could inspire device concepts in oxides-based low dissipation spintronics.

Electrically controllable spin filtering and switching in multiferroic tunneling junctions

Physical Review B, 2007

We present a theoretical investigation of an electrically controllable spin filter based on multiferroic tunneling junction. This spin filter combines the exchange splitting of ferromagnets and asymmetry in energy potential due to the screening of ferroelectric polarization charges at electrodes. Transfer matrix calculations show an enhanced spin filtering efficiency, depending on the magnitude and orientation of ferroelectric polarization. A transition from a positive tunneling magnetoresistance to a negative one is also found. Furthermore, an electric controllable switching between multiple resistive states via magnetoelectric coupling is also described; this will open a different logic programing in future spintronics.

Spin-polarized tunneling, magnetoresistance and interfacial effects in ferromagnetic junctions

The pioneering studies of spin-polarized tunnelling by Meservey and Tedrow in the early 1970s showed that the conduction electrons in ferromagnetic (FM) metals are spin polarized and that the spin is conserved in the tunnelling process. Only recently (1995) improved material fabrication techniques have permitted realization of the Jullie Á re quantitative model, showing that tunnelling in ferromagnet/insulator/ferromagnet (FM/I/FM) junctions should lead to a large junction magnetoresistance (JMR); JMR values greater than 30% have been achieved at room temperature. This recent success has led to several fundamental questions regarding the phenomenon of spin tunnelling and also the development of JMR devices. In this paper, experimental results, such as the dependence on bias, temperature and barrier characteristics of FM/I/FM tunnelling are reviewed brie¯y. The in¯uence of inelastic tunnelling processes, metal at the interface and material properties on the JMR is discussed. The future direction from both the physics and the applications viewpoints, is also covered. } 1. INTRODUCTION Spin-polarized tunnelling (SPT), discovered by Meservey et al. (1970) and Merservey and Tedrow (1971, 1994), laid the foundation to a new ® eld of research. Meservey and Tedrow measured the conduction-electron spin polarization P in magnetic metals and compounds using the Zeeman split quasiparticle density of states in a superconductor as the spin detector. Tunnelling from a ferromagnetic (FM) ® lm, with its uneven spin distribution at the Fermi level E F , into such a spinsplit superconducting Al ® lm re¯ects the spin polarization of the tunnelling electrons coming from the ferromagnet. Values, of P recently measured are higher owing to improved junction preparation conditions including samples grown by molecularbeam epitaxy. Highly polarized tunnelling electrons can also be obtained through a phenomenon called the spin-® lter e ect using magnetic semiconductors such as EuS and EuSe as tunnel barriers (Moodera et al. 1988, 1990, 1993). Jullie Á re (1975) made the ® rst reported magnetoresistance measurement on a ferromagnet/insulator/ferromagnet (FM/I/FM) trilayer junction and interpreted it by stating that the tunnelling current should depend on the relative orientation of the magnetizations of the electrodes. The tunnel junction magnetoresistance (JMR) is

Temporal evolution of spin-polarization in ferromagnetic tunnel junctions

Applied Physics Letters, 2000

The spin polarization of the simple transition-metal ferromagnets Fe, Co, and Ni can be measured using ferromagnet/insulator/superconductor tunneling structures. Measurements, carried out over the past 20 years using superconducting aluminum electrodes and alumina tunneling barriers, have given a wide range of values, especially for Ni. In this letter, we show that high-spin-polarization values are found for Ni using superconducting films formed from Cu-doped aluminum deposited in a high-vacuum sputter-deposition system. However, we find that the magnitude of the spin polarization slowly decreases over time, which we believe to result from a reaction between Ni and alumina. We conclude that the spin-polarization values measured in such studies are strongly influenced by the detailed structure of the ferromagnet-superconductor interface.

Voltage-driven v.s. Current-driven Spin Torque in Anisotropic Tunneling Junctions

2011

Non-equilibrium spin transport in a magnetic tunnel junction comprising a single magnetic layer in the presence of interfacial spin-orbit interaction (SOI) is studied theoretically. The interfacial SOI generates a spin torque of the form {\bf T}=T_{||}{\bf M}x({\bf z}x{\bf M})+T_{\bot}{\bf z}x{\bf M}, even in the absence of an external spin polarizer. For thick and large tunnel barriers, the torque reduces to the perpendicular component, TbotT_{\bot}Tbot, which can be electrically tuned by applying a voltage across the insulator. In the limit of thin and low tunnel barriers, the in-plane torque T∣∣T_{||}T∣∣ emerges, proportional to the tunneling current density. Experimental implications on magnetic devices are discussed.