Sven Cornelissen

Quantized spin-wave modes in magnetic tunnel junction nanopillars

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

Spin-Hall assisted magnetic random access memory

60\ifmmode\times\else\texttimes\fi{}100

Direct experimental measurement of phase-amplitude coupling in spin torque oscillators

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Auto-oscillation and narrow spectral lines in spin-torque oscillators based on MgO magnetic tunnel junctions

75\ifmmode\times\else\texttimes\fi{}150

Performance analysis of MgO-based perpendicularly magnetized tunnel junctions

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Effect of patterning on the saturation magnetization in MgO based nanopillars

105\ifmmode\times\else\texttimes\fi{}190\text{ }{\text{nm}}^{2}

Auto-oscillation threshold and line narrowing in MgO-based spin-torque oscillators

, 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 nonuniformities 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.

Effect of Ta Insertion in Reference Layers of MTJs With Perpendicular Anisotropy

We propose a write scheme for perpendicular spin-transfer torque magnetoresistive random-access memory that significantly reduces the required tunnel current density and write energy. A sub-nanosecond in-plane polarized spin current pulse is generated using the spin-Hall effect, disturbing the stable magnetic state. Subsequent switching using out-of-plane polarized spin current becomes highly efficient. Through evaluation of the Landau-Lifshitz-Gilbert equation, we quantitatively assess the viability of this write scheme for a wide range of system parameters. A typical example shows an eight-fold reduction in tunnel current density, corresponding to a fifty-fold reduction in write energy, while maintaining a 1 ns write time.

High spatial resolution nanoslit SERS for single-molecule nucleobase sensing

We study spin-torque induced oscillations of MgO magnetic tunnel junctions in the time domain. By using the Hilbert transform on the time traces, we obtain for the first time a direct experimental measure of the coupling between the power and the phase fluctuations. We deduce the power restoration rate and we obtain low values for the coupling strength, which is consistent with the weak frequency dependence on the applied voltage.

Interconnects scaling challenge for sub-20nm spin torque transfer magnetic random access memory technology

We demonstrate spin-torque induced coherent auto-oscillation in magnetic tunnel junctions of composition PtMn/CoFe/Ru/CoFeB/MgO/CoFeB and of low resistance-area product. At the generation threshold, we observe a strong line narrowing down to 6 MHz at 300 K and a dramatic increase in oscillator power, yielding spectrally pure oscillations with extremely low flicker noise. The induced auto-oscillations are observed even at zero applied field. The frequency of the oscillation mode, and its dependence with easy and hard axis fields are consistent with an acoustical excitation of the two layers of the synthetic ferrimagnet subsystem. Setting the synthetic ferrimagnet into auto-oscillation requires the current polarity that transfers electrons from the synthetic ferrimagnet to the free layer. In auto-oscillation mode, line jitter is observed such that it is the line envelope that is measured in most cases. The line properties for applied fields near the instability boundaries of the Stoner astroid of the free l...