| 1. |
- Le, Quang Tuan, 1976-, et al.
(författare)
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Ultra-high frequency tunability in low-current and low-field spin-torque oscillators based on perpendicular magnetic tunnel junctions
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Annan publikation (populärvet., debatt m.m.)abstract
- We demonstrate ultra-high frequency tunability of up to 4.4 GHz/mA, and low threshold currents of about -21 $\mu$A, in spin-torque oscillators based on CoFeB/MgO/CoFeB magnetic tunnel junctions, in which both free and fixed layers have perpendicular magnetic anisotropy (PMA). By using different thicknesses of the two CoFeB layers, their individual PMA strengths can be tailored to achieve significant relative misalignment of their respective magnetizations in moderate in-plane fields. We observe a broad maximum in both the device resistance and the generated microwave power around maximum misalignment. Maximum frequency tunability is observed at low-to-moderate fields and decrease rapidly after maximum misalignment.
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| 2. |
- Chung, Sunjae, et al.
(författare)
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Tunable spin configuration in [Co/Ni]-NiFe spring magnets
- 2013
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 46:12, s. 125004-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate a tunable spin configuration in [Co/Ni](4)/Co-NiFe exchange spring magnets. The strong perpendicular magnetic anisotropy of the Co/Ni multilayer, which competes with the in-plane shape anisotropy of the Ni81Fe19 (Py) layer, allows for unique magnetic configurations. By varying the NiFe thickness (t(NiFe)) from 2.6 to 3.0 nm, we show that the magnetization tilt angle can be easily tuned from completely out-of-plane (0 degrees) to in-plane (90 degrees). This transition, which occurs for a small range of t(NiFe), can be estimated from the major loop remanence and one-dimensional micromagnetic calculations. These tunable magnetization tilt spring magnets are highly promising for future applications in spin-transfer torque-based devices.
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| 3. |
- Nguyen, Thi Ngooc Ahn, et al.
(författare)
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Co/Pd (4)-Co-Pd-NiFe spring magnets with highly tunable and uniform magnetization tilt angles
- 2012
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 324:22, s. 3929-3932
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Tidskriftsartikel (refereegranskat)abstract
- By varying the Pd thickness (t(Pd)) from 0 to 8 nm in [Co/Pd](4)/Co/Pd(t(Pd))/NiFe exchange springs, we demonstrate (i) continuous tailoring of the exchange coupling between a [Co/Pd](4)/Co layer with perpendicular anisotropy, and a NiFe layer with an in-plane easy axis, (ii) tuning of the NiFe out-of-plane magnetization angle from 20 degrees to 80 degrees, and(iii) an up to two-fold increase in the NiFe damping. The partial decoupling also results in a highly uniform NiFe magnetization. These properties make [Co/Pd](4)/Co/Pd(t(Pd))/NiFe spring magnets ideal candidates for use as tilted polarizers, by combining stable and well-defined spin directions of its carriers with a high degree of angular freedom. (C) 2012 Elsevier B.V. All rights reserved.
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| 4. |
- Nguyen, T. N. Anh, et al.
(författare)
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[Co/Pd]-NiFe exchange springs with tunable magnetization tilt angle
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 98:17
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Tidskriftsartikel (refereegranskat)abstract
- We investigate exchange coupled [Co/Pd]5–NiFe thin films. Due to competition between the in-plane shape anisotropy of the NiFe and strong perpendicular magnetic anisotropy of the [Co/Pd]5 multilayer, unique magnetic configurations are achievable. In particular, we explore the out-of-plane magnetization tilt angle of the NiFe layer. Experimental results, based on conventional magnetometry, ferromagnetic resonance, and magnetic force microscopy, agree well with one-dimensional micromagnetic simulations. We find that the tilt angle is highly tunable (0°–60°) over a small range of NiFe thicknesses (4.8–8 nm). Potential applications for high power, zero-field operation spin torque oscillators are discussed.
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| 5. |
- Nguyen, Thi Ngoc Anh, et al.
(författare)
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Investigation of the Tunability of the Spin Configuration Inside Exchange Coupled Springs of Hard/Soft Magnets
- 2014
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Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 50:6, s. 2004906-
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic multilayer (ML) structures comprising a perpendicular magnetic anisotropy (PMA) layer coupled to an in-plane magnetic anisotropy (IMA) layer are promising materials for zero/low field operating spin-torque oscillators and bit patterned recording media. The magnetization tilt angle can be easily tuned by varying the IMA layer thickness due to the competition between PMA and IMA layers. To explore the underlying magnetization reversal mechanism and to further understand the control of tilt angle and uniformity of the magnetization, the IMA (NiFe, Co, and CoFeB)/PMA (Co/Pd MLs) exchange spring systems are systematically studied. Experimental data obtained from magnetometry show good agreement with 1-D micromagnetic simulations, allowing us to design tunable exchange coupled spring as a function of IMA thickness.
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| 6. |
- Sani, Sohrab R, et al.
(författare)
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Current induced vortices in multi-nanocontact spin-torque devices
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:7, s. 07C913-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate spin transfer torque (STT) switching in multi-nanocontact STT devices fabricated using hole mask colloidal lithography. We also study the STT device resistance and switching properties as a function of applied magnetic field and nanocontact current. At low nanocontact current, magnetoresistance measurements show sharp, single-step switching at low switching fields. When the current is increased, the switching becomes multistep, and the switching field increases dramatically. We explain these results as arising from a transition from a predominantly single domain like switching to switching involving a vortex state. Micromagnetic simulations corroborate this picture, indicating that a single magnetic vortex nucleates in between the nanocontacts through the influence from the total Oersted field generated by the nanocontact ensemble.
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