Quantized spin wave modes in magnetic tunnel junction nanopillars

Abstract

We present an experimental and theoretical study of the magnetic field dependence of the mode frequency of thermally excited spin waves in rectangular shaped nanopillars of lateral sizes 60x100, 75x150, and 105x190 nm2, patterned from MgO-based magnetic tunnel junctions. The spin wave frequencies were measured using spectrally resolved electrical noise measurements. In all spectra, several independent quantized spin wave modes have been observed and could be identified as eigenexcitations of the free layer and of the synthetic antiferromagnet of the junction. Using a theoretical approach based on the diagonalization of the dynamical matrix of a system of three coupled, spatially confined magnetic layers, we have modeled the spectra for the smallest pillar and have extracted its material parameters. The magnetization and exchange stiffness constant of the CoFeB free layer are thereby found to be substantially reduced compared to the corresponding thin film values. Moreover, we could infer that the pinning of the magnetization at the lateral boundaries must be weak. Finally, the interlayer dipolar coupling between the free layer and the synthetic antiferromagnet causes mode anticrossings with gap openings up to 2 GHz. At low fields and in the larger pillars, there is clear evidence for strong non-uniformities of the layer magnetizations. In particular, at zero field the lowest mode is not the fundamental mode, but a mode most likely localized near the layer edges.

16 pages, 4 figures, (re)submitted to PRB

References in corpus (5)

• Bias-driven large power microwave emission from MgO-based tunnel magnetoresistance devices
• Spin-transfer-driven ferromagnetic resonance of individual nanomagnets
• Current-driven microwave oscillations in current perpendicular-to-plane spin-valve nanopillars
• Thermal-magnetic noise measurement of spin-torque effects on ferromagnetic resonance in MgO-based magnetic tunnel junctions
• Auto-oscillation threshold and line narrowing in MgO-based spin-torque oscillators

Cited by in corpus (17)

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• Identification and selection rules of the spin-wave eigen-modes in a normally magnetized nano-pillar
• Resonant Nonlinear Damping of Quantized Spin Waves in Ferromagnetic Nanowires
• Spin torque ferromagnetic resonance with magnetic field modulation
• Bias dependence of perpendicular spin torque and of free and fixed layer eigenmodes in MgO-based nanopillars
• Spin-Torque Diode Measurements of MgO-Based Magnetic Tunnel Junctions with Asymmetric Electrodes
• Ultrathin perpendicular free layers for lowering the switching current in STT-MRAM
• Influence of MgO tunnel barrier thickness on spin-transfer ferromagnetic resonance and torque in magnetic tunnel junctions
• Pushing down the lateral dimension of single and coupled magnetic dots to the nanometric scale: characteristics and evolution of the spin-wave eigenmodes
• Evolution of perpendicular magnetized tunnel junctions upon annealing
• Measuring a population of spin waves from the electrical noise of an inductively coupled antenna
• Spin-wave thermal population as temperature probe in Magnetic Tunnel Junctions
• Influence of interlayer coupling on the spin torque driven excitations in a spin torque oscillator
• CoFeAlB alloy with low damping and low magnetization for spin transfer torque switching
• Detection of spin torque magnetization dynamics through low frequency noise
• Spin-torque nano-oscillator based on two in-plane magnetized synthetic ferrimagnets