Tunable spin configuration in [Co/Ni]-NiFe spring magnets

Chung, Sunjae; Mohseni, Seyed Majid; Fallahi, Vahid; Nguyen, Tu N.; Benatmane, Nadjib; Dumas, Randy K.; Åkerman, Johan

doi:10.1088/0022-3727/46/12/125004

Cited by 31 publications

(26 citation statements)

References 24 publications

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“…In this work, we investigate the role of the soft layer on the magnetic anisotropy, domain structure and damping in exchange-coupled [Co/Pd] 5 /NiFe films. The results are extended to a wider range of NiFe layer thicknesses, from 3 nm to 80 nm, compared with previous studies 16,17,19 . Also we characterize damping and anisotropy by ferromagnetic resonance measurements, and domain structure by magnetic imaging and simulation.…”

Section: 15mentioning

confidence: 67%

Magnetic structure and anisotropy of[Co/Pd]5/NiFemultilayers

et al. 2015

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The magnetization behavior, magnetic anisotropy and domain congurations of Co/Pd multilayers with perpendicular magnetic anisotropy capped with permalloy is investigated using magnetometry, magnetic force microscopy and ferromagnetic resonance. The thickness of the Ni80Fe20 layer in [Co/Pd]5/NiFe(t) was varied from t = 0 nm to 80 nm in order to study the interplay between the anisotropy and magnetization directions of the Co/Pd and the NiFe. By varying the thickness of the NiFe layer the net anisotropy changes sign, but domains with plane-normal magnetization are present even for the thickest NiFe. Ferromagnetic resonance measurements show a decrease in damping with increasing NiFe thickness. The results demonstrate how the magnetic behavior of mixed-anisotropy thin films can be controlled.

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Section: 15mentioning

confidence: 67%

Magnetic structure and anisotropy of[Co/Pd]5/NiFemultilayers

et al. 2015

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“…While a fully perpendicular STNO, such as that assumed in the original prediction of droplets [40], would have the lowest nucleation current, it would on the other hand also not have any output signal, since the symmetry of the magnetodynamics would not generate a time-varying STNO resistance. Instead we argue that a fixed layer based on tilted anisotropy materials [51][52][53][54][55][56][57][58][59][60] would be ideal for droplet nucleation and operation. In Fig.…”

Section: Magnetic Droplet Nucleation Current Vs Fieldmentioning

confidence: 88%

Magnetic droplet solitons in orthogonal spin valves

Chung

Mohseni

Eklund

et al. 2015

Low Temperature Physics

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We review the recent experimental advancements in the realization and understanding of magnetic droplet solitons generated by spin transfer torque in orthogonal nanocontact based spin torque nanooscillators (STNOs) fabricated on extended spin valves and spin valve nanowires. The magnetic droplets are detected and studied using the STNO microwave signal and its resistance, the latter both quasistatically and time-resolved. The droplet nucleation current is found to have a minimum at intermediate magnetic field strengths and the nature of the nucleation changes gradually from a single sharp step well above this field, mode-hopping around the minimum, and continuous at low fields. The mode-hopping and continuous transitions are ascribed to droplet drift instability and re-nucleation at different time scales, which is corroborated by time-resolved measurements. We argue that the use of tilted anisotropy fixed layers could reduce the nucleation current further, move the nucleation current minimum to lower fields, and potentially remove the need for an applied magnetic field altogether. Finally, evidence of an edge mode droplet in a nanowire is presented. PACS: 75.30.Ds Spin waves;75.75.-c Magnetic properties of nanostructures.

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“…Recently, an alternative and much more versatile approach was reported where exchange springs combining materials with out-of-plane (OOP) and IP anisotropies provide a wide and tunable range of tilt angles [40][41][42]. Using different thicknesses of the OOP and IP layers and different OOP-IP coupling strengths, the average tilt angle, the details of the magnetization profile, and even the damping, can be varied with great freedom.…”

mentioning

confidence: 99%

Depth-Dependent Magnetization Profiles of Hybrid Exchange Springs

et al. 2014

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We report on the magnetization depth profile of a hybrid exchange spring system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to a CoFeB thin film with in-plane anisotropy. The competition between these two orthogonal anisotropies promotes a strong depth dependence of the magnetization orientation. The angle of the magnetization vector is sensitive both to the strength of the individual anisotropies and to the local exchange constant, and is thus tunable by changing the thickness of the CoFeB layer and by substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic depth profiles are directly probed by element specific x-ray magnetic circular dichroism (XMCD) of the Co, Fe, and Ni layers located at different average depths. The experimental results are corroborated by micromagnetic simulations.PACS numbers: 75.30. Gw, 75.30.Et, 78.20.Ls, 75.70.Cn a Author to whom correspondence should be addressed. Electronic mail: anhntn@kth.se. 2The phenomenon of spin transfer torque (STT) [1][2][3], in which a spin-polarized current transfers angular momentum to a magnetic layer, has brought about novel applications such as spin torque oscillators (STOs) [4][5][6][7] and spin transfer torque magnetoresistive random access memory (STT-MRAM) [8][9][10]. While initially based on magnetic materials with in-plane (IP) magnetic anisotropy, the realization that such materials lead to unnecessarily high STT-MRAM switching currents, poor memory retention, poor scalability [11], and high-field operation of STOs [12], there is now a rapidly growing interest in fabricating STT devices based on perpendicular magnetic anisotropy (PMA) materials. Recent tailoring of PMA materials and their interfaces have demonstrated low switching currents, high switching speed, good thermal stability, future scalability [9,[13][14][15], and low-to zero-field operation of STOs [16][17][18][19][20].Building upon these successes, the natural extension of using PMA materials is to also investigate the potential of devices in which the magnetization is tilted with respect to the surface normal. Such materials allow for additional control of the magnetization dynamics in magnetic nanostructures [17,[21][22][23], and hint at yet improved STT-MRAM switching behavior and thermal stability [24][25][26][27][28][29]. For STOs, tilted materials offer a route to improve their microwave generation properties, both in terms of higher output power and low-to zero-field operation [17,[21][22][23]28,[30][31][32].Recently, tilted materials have also been shown to have potential for current-driven domain wall motion [33]. The influence of a tilted anisotropy is stronger than simply tilting the applied field [34] as a mere 5 degree misalignment between the free and the fixed layer in magnetic tunnel junctions (MTJs) can reduce the switching current by 36%, the switching time by 30%, and improve the switching current distribution [35].Materials with tilted anisotropies have been realized using collimated oblique sputtering [36], depos...

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Tunable spin configuration in [Co/Ni]-NiFe spring magnets

Cited by 31 publications

References 24 publications

Magnetic structure and anisotropy of[Co/Pd]5/NiFemultilayers

Magnetic structure and anisotropy of[Co/Pd]5/NiFemultilayers

Magnetic droplet solitons in orthogonal spin valves

Depth-Dependent Magnetization Profiles of Hybrid Exchange Springs

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