Ferromagnetic resonance of exchange-coupled perpendicularly magnetized bilayers

Devolder, T.

doi:10.1063/1.4947227

Cited by 16 publications

(11 citation statements)

References 26 publications

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“…On the other hand, we can obtain the difference of PMA ( 2 − 1 ) 2 ⁄ by linear fitting of the experimental data from -190 to 130 mT with Eq. (5) for antiparallel state, because the intersection magnetic field of the two antiferromagnetic resonance modes is given by ( 2 − 1 ) 2 ⁄ which represents the difference of the effective magnetic field between the two ferromagnetic layers as predicted in a previous report 28) . While our films consist of two ferromagnetic layers with the same structure, the experimental results shown in Fig.…”

Section: Discussionmentioning

confidence: 64%

Spin Wave Resonance in Perpendicularly Magnetized Synthetic Antiferromagnets

et al. 2021

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We report antiferromagnetic spin wave resonance in perpendicularly magnetized synthetic antiferromagnets consisting of Co/Ni multilayers and a thin Ru spacer layer. Two resonance modes were observed in the finite range of the out-of-plane bias magnetic field, where two magnetic moments separated by the Ru layer were antiferromagnetically aligned. These two modes show an opposite dependence on the bias magnetic field and correspond to right-and left-handed polarized spin waves. We also theoretically derive the spin wave dispersion for the perpendicularly magnetized synthetic antiferromagnets on the basis of an equation of motion. Our experimental results show good agreement with the theoretical analysis.

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Section: Discussionmentioning

confidence: 64%

Spin Wave Resonance in Perpendicularly Magnetized Synthetic Antiferromagnets

et al. 2021

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“…Over the years, different generations of PMA-MTJ stacks of been studied: some showed clear BH [9,10,13], some others did not [14][15][16][17]. Since our objective is to understand the phenomenon of BH, we have selected the MTJ stacks where BH is clearly happening.…”

Section: Samples and Methodsmentioning

confidence: 99%

“…and 6 was based on a bias-dependent sign reversal of the STT acting on the FL: C 8 Å, 400 • C RL-SPL exchange coupling (mJ/m 2 ) 0.0712 , 0.2120 , 0.37 21 0.2212 ‡ J0 = 0.3322 † …”

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confidence: 99%

Back hopping in spin transfer torque switching of perpendicularly magnetized tunnel junctions

et al. 2020

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We analyze the phenomenon of back hopping in spin-torque induced switching of the magnetization in perpendicularly magnetized tunnel junctions. The analysis is based on single-shot time-resolved conductance measurements of the pulse-induced back hopping. Studying several material variants reveals that the back hopping is a feature of the nominally fixed system of the tunnel junction. The back hopping is found to proceed by two sequential switching events that lead to a final state P of conductance close to-but distinct from-that of the conventional parallel state. The P state does not exist at remanence. It generally relaxes to the conventional antiparallel state if the current is removed. The P state involves a switching of the sole spin-polarizing part of the fixed layers. The analysis of literature indicates that back hopping occurs only when the spin-polarizing layer is too weakly coupled to the rest of the fixed system, which justifies a posteriori the mitigation strategies of back hopping that were implemented empirically in spin-transfer-torque magnetic random access memories.

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“…There are two main variants of these resonance techniques. The socalled conventional FMR and its modern version the vector network analyzer 2 (VNA)-FMR are established technique to harness the coupling of microwave photons to the magnetization eigenmodes to measure to anisotropy fields 1 , demagnetizing fields, exchange stiffness 3 , interlayer exchange 4 and spin-pumping 5 , most often at film level. More recent methods, like the increasingly popular spin-transfer-torque-(STT)-FMR, are developed 6 to characterize the magnetization dynamics of magnetic bodies embodied in electrical devices possessing a magneto-resistance of some kind.…”

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confidence: 99%

Using rf voltage induced ferromagnetic resonance to study the spin-wave density of states and the Gilbert damping in perpendicularly magnetized disks

Devolder

2017

Phys. Rev. B

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We study how the shape of the spinwave resonance lines in rf-voltage induced FMR can be used to extract the spin-wave density of states and the Gilbert damping within the precessing layer in nanoscale magnetic tunnel junctions that possess perpendicular magnetic anisotropy. We work with a field applied along the easy axis to preserve the cylindrical symmetry of the uniaxial perpendicularly magnetized systems. We first describe the experimental set-up to study the susceptibility contributions of the spin waves in the field-frequency space. We then identify experimentally the maximum device size above which the spinwaves confined in the free layer can no longer be studied in isolation as the linewidths of their discrete responses make them overlap into a continuous density of states. The rf-voltage induced signal is the sum of two voltages that have comparable magnitudes: a first voltage that originates from the linear transverse susceptibility and rectification by magneto-resistance and a second voltage that arises from the non-linear longitudinal susceptibility and the resultant time-averaged change of the exact micromagnetic configuration of the precessing layer. The transverse and longitudinal susceptibility signals have different dc bias dependences such that they can be separated by measuring how the device rectifies the rf voltage at different dc bias voltages. The transverse and longitudinal susceptibility signals have different lineshapes; their joint studies in both fixed field-variable frequency, or fixed frequency-variable field configurations can yield the Gilbert damping of the free layer of the device with a degree of confidence that compares well with standard ferromagnetic resonance. Our method is illustrated on FeCoB-based free layers in which the individual spin-waves can be sufficiently resolved only for disk diameters below 200 nm. The resonance line shapes on devices with 90 nm diameters are consistent with a Gilbert damping of 0.011. A single value of the damping factor accounts for the line shape of all the spin-waves that can be characterized. This damping of 0.011 exceeds the value of 0.008 measured on the unpatterned films, which indicates that device-level measurements are needed for a correct evaluation of dissipation.

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Ferromagnetic resonance of exchange-coupled perpendicularly magnetized bilayers

Cited by 16 publications

References 26 publications

Spin Wave Resonance in Perpendicularly Magnetized Synthetic Antiferromagnets

Spin Wave Resonance in Perpendicularly Magnetized Synthetic Antiferromagnets

Back hopping in spin transfer torque switching of perpendicularly magnetized tunnel junctions

Using rf voltage induced ferromagnetic resonance to study the spin-wave density of states and the Gilbert damping in perpendicularly magnetized disks

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