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Free- and reference-layer magnetization modes vs.~in-plane magnetic field in  a magnetic tunnel junction with perpendicular magnetic easy axis
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. NanOsc AB.ORCID iD: 0000-0003-3605-8872
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. (Applied Spintronics)ORCID iD: 0000-0001-9107-3309
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. Univ Gothenburg, Sweden.
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2016 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795Article in journal (Other (popular science, discussion, etc.)) Accepted
Abstract [en]

We study the magnetodynamic modes of a magnetic tunnel junction with perpendicular magnetic easy axis (p-MTJ) in in-plane magnetic fields using device-level ferromagnetic resonance spectroscopy. We compare our experimental results to those of micromagnetic simulations of the entire p-MTJ. Using an iterative approach to determine the material parameters that best fit our experiment, we find excellent agreement between experiments and simulations in both the static magnetoresistance and magnetodynamics in the free and reference layers. From the micromagnetic simulations, we determine the spatial mode profiles, the localization of the modes and, as a consequence, their distribution in the frequency domain due to the inhomogeneous internal field distribution inside the p-MTJ under different applied field regimes. We also conclude that the excitation mechanism is a combination of the microwave voltage modulated perpendicular magnetic anisotropy, the microwave Oersted field, and the spin-transfer torque generated by the microwave current.

Place, publisher, year, edition, pages
American Physical Society , 2016.
National Category
Condensed Matter Physics
Research subject
Materials Science and Engineering; Physics
Identifiers
URN: urn:nbn:se:kth:diva-191175OAI: oai:DiVA.org:kth-191175DiVA: diva2:955244
Funder
Swedish Foundation for Strategic Research
Note

QC 20160829

Available from: 2016-08-24 Created: 2016-08-24 Last updated: 2017-11-28Bibliographically approved
In thesis
1. Magnetodynamics in Spin Valves and Magnetic Tunnel Junctions with Perpendicular and Tilted Anisotropies
Open this publication in new window or tab >>Magnetodynamics in Spin Valves and Magnetic Tunnel Junctions with Perpendicular and Tilted Anisotropies
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Spin-torque transfer (STT) effects have brought spintronics ever closer to practical electronic applications, such as MRAM and active broadband microwave spin-torque oscillator (STO), and have emerged as an increasingly attractive field of research in spin dynamics. Utilizing materials with perpendicular magnetic anisotropy (PMA) in such applications offers several great advantages such as low-current, low-field operation combined with high thermal stability. The exchange coupling that a PMA thin film exerts on an adjacent in-plane magnetic anisotropy (IMA) layer can tilt the IMA magnetization direction out of plane, thus creating a stack with an effective tilted magnetic anisotropy. The tilt angle can be engineered via both intrinsic material parameters, such as the PMA and the saturation magnetization, and extrinsic parameters, such as the layer thicknesses.

      STOs can be fabricated in one of a number of forms—as a nanocontact opening on a mesa from a deposited pseudospin-valve (PSV) structure, or as a nanopillar etching from magnetic tunneling junction (MTJ)—composed of highly reproducible PMA or predetermined tilted magnetic anisotropy layers.

      All-perpendicular CoFeB MTJ STOs showed high-frequency microwave generation with extremely high current tunability, all achieved at low applied biases. Spin-torque ferromagnetic resonance (ST-FMR) measurements and analysis revealed the bias dependence of spin-torque components, thus promise great potential for direct gate-voltage controlled STOs.

      In all-perpendicular PSV STOs, magnetic droplets were observed underneath the nanocontact area at a low drive current and low applied field. Furthermore, preliminary results for microwave auto-oscillation and droplet solitons were obtained from tilted-polarizer PSV STOs. These are promising and would be worth investigating in further studies of STT driven spin dynamics.

Abstract [sv]

Effekter av spinnvridmoment (STT) har fört spinntroniken allt närmare praktiska elektroniska tillämpningar, såsom MRAM och den spinntroniska mikrovågsoscillatorn (STO), och har blivit ett allt mer attraktivt forskningsområde inom spinndynamik. Användning av material med vinkelrät magnetisk anisotropi (PMA) i sådana tillämpningar erbjuder flera stora fördelar, såsom låg strömförbrukning och funktion vid låga fält i kombination med hög termisk stabilitet. Den utbyteskoppling (”exchange bias”) en PMA-tunnfilm utövar på ett intilliggande skikt med magnetisk anisotropi i planet (IMA) kan få IMA-magnetiseringsriktningen att vridas ut ur planet, vilket ger en materialstack med en effektivt sett lutande magnetisk anisotropi. Lutningsvinkeln kan manipuleras med både inre materialparametrar, såsom PMA och mättningsmagnetisering, och yttre parametrar, såsom skikttjocklekarna.

STO:er kan tillverkas som flera olika typer - som en nanokontaktsöppning på en s.k. mesa av en deponerad pseudospinnventilstruktur (PSV) eller som en nanotråd etsad ur en magnetisk tunnlingsövergång (MTJ) –och bestå av mycket reproducerbar PMA eller av skikt med på förhand bestämt lutning av dess magnetiska anisotropi.

MTJ-STO:er av CoFeB med helt vinkelrät anisotropi visar högfrekvent mikrovågsgenerering med extremt stort frekvensomfång hos strömstyrningen, detta vid låg biasering. Mätning och analys av spinnvridmoments-ferromagnetisk resonans (ST-FMR) avslöjade ett biasberoende hos spinnvridmomentskomponenter, vilket indikerar en stor potential för direkt gate-spänningsstyrda STO:er.

I helt vinkelräta PSV-STO:er observerades magnetiska droppar under nanokontaktområdet vid låg drivström och lågt pålagt fält. Dessutom erhölls preliminära resultat av mikrovågssjälvsvängning och av s.k. ”droplet solitons” hos PSV-STO:er med lutande polarisator. Dessa är lovande och skulle vara värda att undersökas i ytterligare studier av STT-driven spinndynamik.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 83 p.
Series
TRITA-ICT, 2016:21
Keyword
perpendicular magnetic anisotropy, tilted-polarizer, spintronics, STT, MTJ, pseudospin-valve, STO, ST-FMR, magnonics, magnetic droplet, droplet nucleation, droplet annihilation, vinkelrät magnetisk anisotropi, lutande polarisator, spinntronik, STT, MTJ, pseudospinnventil, STO, ST-FMR, magnonics, magnetisk droppe, nukleering av droppe, anihilering av droppe.
National Category
Nano Technology Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-191176 (URN)978-91-7729-072-8 (ISBN)
External cooperation:
Public defence
2016-09-30, Sal C, Electrum, Kungl Tekniska högskolan, Kistagången 16, Kista, 13:00 (English)
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Supervisors
Note

QC 20160829

Available from: 2016-08-29 Created: 2016-08-24 Last updated: 2016-08-29Bibliographically approved

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