Conductance, magnetoresistance, and interlayer exchange coupling in magnetic tunnel junctions with nonmagnetic metallic spacers and finite thick ferromagnetic layers (original) (raw)
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Journal of Applied Physics, 1998
Based on the two-band model and free-electron approximation, we study the magnetism and transport properties of tunnel junctions with nonmagnetic interlayers ͑NM͒ between the ferromagnetic electrodes and tunneling barrier. We find that properties of the junctions are intermediate between tunnel junctions and metallic magnetic multilayers. The mean conductance, tunnel magnetoresistance, and interlayer coupling are all the oscillatory functions of the thickness of NM. It suggests that weak antiferromagnetic coupling can be attained by controlling the thickness of NM. Our results have potential in designing spin-polarized tunneling devices with large field sensitivity.
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
Tunnel magnetoresistance versus micromagnetism in magnetic tunnel junctions
Journal of Applied Physics, 2000
The impact of the micromagnetic configuration within the ferromagnetic layers on transport properties of hard/soft magnetic tunnel junctions is presented. An artificial ferrimagnetic ͑AFi͒ trilayer structure is used as a magnetically hard subsystem. Fluctuations in magnetization in the AFi affect the resistance of the tunnel junctions and are fully reflected in the shape and amplitude of the tunnel magnetoresistance signal.
Tunneling Magnetoresistance in Noncollinear Antiferromagnetic Tunnel Junctions
Physical Review Letters
Antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics driven by the advantages of antiferromagnets producing no stray fields and exhibiting ultrafast magnetization dynamics. The efficient method to detect an AFM order parameter, known as the Néel vector, by electric means is critical to realize concepts of AFM spintronics. Here, we demonstrate that non-collinear AFM metals, such as Mn3Sn, exhibit a momentum dependent spin polarization which can be exploited in AFM tunnel junctions to detect the Néel vector. Using first-principles calculations, we predict a tunneling magnetoresistance (TMR) effect as high as 300% in AFM tunnel junctions with Mn3Sn electrodes, where the junction resistance depends on the relative orientation of their Néel vectors and exhibits four non-volatile resistance states. We argue that the spin-split band structure and the related TMR effect can also be realized in other non-collinear AFM metals like Mn3Ge, Mn3Ga, Mn3Pt, and Mn3GaN. Our work provides a robust method for detecting the Néel vector in non-collinear antiferromagnets via the TMR effect, which may be useful for their application in AFM spintronic devices.
Interpretation of the magnetoresistance in doped magnetic tunnel junctions
The European Physical Journal B - Condensed Matter, 2002
We present a quantum mechanical model of the magnetoresistance in ferromagnetic tunnel junctions artificially doped by the introduction of layers of impurities in the middle of the barrier. The electron transport across the barrier is described by a combination of direct tunneling, tunneling assisted by spin-conserving scattering and tunneling assisted by spin-flip scattering. With this model, we interpret recent experimental results concerning the dependence of the TMR amplitude on the amount of impurities in the barrier and on temperature. PACS. 75.70.-i Magnetic properties of thin films, surfaces, and interfaces -73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects) -85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
Resonant tunnel magnetoresistance in double-barrier planar magnetic tunnel junctions
Physical Review B, 2011
We present a theoretical approach to calculate the spin-dependent current and tunnel magnetoresistance (TMR) in a double-barrier magnetic tunnel junction (DMTJ), in which the magnetization of the middle ferromagnetic metal layer can be aligned parallel or antiparallel in relation to the fixed magnetizations of the left and right ferromagnetic electrodes. The electron transport through the DMTJ is considered as a three-dimensional problem, taking into account all transmitting electron trajectories as well as the spin-dependent momentum conservation law. The dependence of the transmission coefficient and spin-polarized currents on the applied voltage is derived as an exact solution to the quantum-mechanical problem for the spin-polarized transport. In the range of the developed physical model, the resonant tunneling, nonresonant tunneling, and enhanced spin filtering can be explained; the simulation results are in good agreement with experimental data.
Enhanced tunneling magnetoresistance in Fe∕ZnSe double junctions: Ab initio calculations
Physical Review B, 2006
We calculate the tunneling magnetoresistance (TMR) of Fe|ZnSe|Fe|ZnSe|Fe (001) double magnetic tunnel junctions as a function of the in-between Fe layer's thickness, and compare these results with those of Fe|ZnSe|Fe simple junctions. The electronic band structures are modeled by a parametrized tight-binding Hamiltonian fitted to ab initio calculations, and the conductance is calculated within the Landauer formalism expressed in terms of Green's functions. We find that the conductances for each spin channel and the TMR strongly depend on the in-between Fe layer's thickness, and that in some cases they are enhanced with respect to simple junctions, in qualitative agreement with recent experimental studies performed on similar systems. By using a 2D double junction as a simplified system, we show that the conductance enhancement can be explained in terms of the junctions energy spectrum. These results are relevant for spintronics because they demonstrate that the TMR in double junctions can be tuned and enhanced by varying the in-between metallic layer's thickness.