Vortex pinning at individual defects in magnetic nanodisks

Rahm, M.; Biberger, J.; Umansky, V.; Weiss, Dieter

doi:10.1063/1.1558255

Cited by 48 publications

(43 citation statements)

References 9 publications

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“…As a result it is important to gain an understanding of domain wall dynamics. The presence of impurities and intrinsic material defects, found in all real samples, affects the mobility of domain walls causing them to be trapped at pinning sites [4][5][6][7][8]. Thin disks composed of soft magnetic materials have been shown to exhibit a ground-state vortex structure, which is characterized by a single large curl of in-plane magnetization and a central vortex core region of magnetization normal to the plane [9][10][11].…”

Section: Introductionmentioning

confidence: 99%

“…Previous work has studied the dynamics of magnetic vortices and their interaction with pinning sites by means of micro-Hall magnetometry [4,14,15], Lorentz transmission electron microscopy [5,16,17], and scanning x-ray transmission microscopy [18]. Optical probing by means of time-resolved Kerr microscopy has allowed for the measurement of gyrotropic frequency suppression in the presence of naturally occurring pinning sites [6,19,20].…”

Section: Introductionmentioning

confidence: 99%

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Magneto-optical imaging of vortex domain deformation in pinning sites

Badea

Frey

Berezovsky

2015

Journal of Magnetism and Magnetic Materials

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a b s t r a c tWe use a sensitive magneto-optical microscopy technique to image the magnetization response of micron-scale ferromagnetic disks to changes in applied magnetic field. This differential technique relies on a modulated applied magnetic field which allows us to measure changes in magnetization 1% < with submicron resolution. The disks are magnetized in single vortex domains, with defects in the material serving to pin the vortex core at particular positions. By applying a small AC magnetic field, we measure the deformation of the magnetization while the core remains pinned. We can also characterize the strength of the pinning site by increasing the AC magnetic field to unpin the vortex core. While pinned, we find that the magnetization away from the core reorients slightly to better align with an applied field. Additionally, an applied field causes the pinned core itself to tilt in the direction of the field. Once the field is large enough to unpin the core, this tilt disappears, and the core instead translates across the disk.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Magneto-optical imaging of vortex domain deformation in pinning sites

Badea

Frey

Berezovsky

2015

Journal of Magnetism and Magnetic Materials

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“…The additional switching near H ll = ±100 Oe corresponds to vortex nucleation, which reduces the GMR from its maximum value in the uniform, antiparallel configuration. Discrete steps in dV/dI are observed for both out-of-plane (not shown) and in-plane applied fields, resulting from intermittent pinning of vortex due to material defects and device shape imperfections 24,25 . Due to the thermally activated nature of the vortex nucleation, in some scans, such as the one shown in Fig.…”

mentioning

confidence: 99%

Magnetic vortex oscillator driven by d.c. spin-polarized current

et al. 2007

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Abstract:Transfer of angular momentum from a spin-polarized current to a ferromagnet provides an efficient means to control the dynamics of nanomagnets. A peculiar consequence of this spin-torque, the ability to induce persistent oscillations of a nanomagnet by applying a dc current, has previously been reported only for spatially uniform nanomagnets. Here we demonstrate that a quintessentially nonuniform magnetic structure, a magnetic vortex, isolated within a nanoscale spin valve structure, can be excited into persistent microwave-frequency oscillations by a spin-polarized dc current. Comparison to micromagnetic simulations leads to identification of the oscillations with a precession of the vortex core. The oscillations, which can be obtained in essentially zero magnetic field, exhibit linewidths that can be narrower than 300 kHz, making these highly compact spin-torque vortex oscillator devices potential candidates for microwave signalprocessing applications, and a powerful new tool for fundamental studies of vortex dynamics in magnetic nanostructures. Pribiag et al.1A spin-polarized electron current can apply a torque on the local magnetization of a ferromagnet. This spin-transfer effect 1,2 provides a new method for manipulating magnetic systems at the nanoscale without the application of magnetic fields and is expected to lead to future data storage and information processing applications 3 . Experiments have demonstrated that spin-torque can be used to induce current-controlled hysteretic switching, as well as to drive persistent microwave dynamics in spin-valve devices 3,4,5,6,7,8,9,10,11,12 . While it is known that spin-torque switching of a magnetic element can sometimes occur via non-uniform magnetic states 13 , a central remaining question is whether spin-torque can be used to efficiently excite steady-state magnetization oscillations in strongly non-uniform magnetic configurations in a manner suitable for fundamental investigations of nanomagnetic dynamics and improved device performance. A relatively simple type of non-uniform magnetic structure is a magnetic vortex, the lowest-energy configuration of magnetic structures just above the singledomain length scale 14 . Previous studies, typically performed on single-layer permalloy (Py) structures, focused on the transient or resonant response of a magnetic vortex to an applied magnetic field and identified the lowest excitation mode of a vortex as a gyrotropic precession of the core 15,16,17,18 . It has also been demonstrated that the vortex core polarization can be efficiently switched by short radio-frequency magnetic field pulses 19 . Recently, the spin-transfer effect has been used to drive a magnetic vortex into resonant precession by means of an alternating current incident on a single Py dot 20 . Here we report by means of direct frequency-domain measurements that a dc spinpolarized current can drive highly coherent gigahertz-frequency steady-state oscillations of the magnetic vortex in a nanoscale magnetic device. The high sensitivity of ou...

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“…The vortex core is pinned by the triangular defect directly as the vortex state is formed in the disk. It is the typical reversal mode similar to the condition of a disk with a hole-shaped defect [26]. As the tilt angle y ¼ 90 3 , there are four jumps appear in the hysteresis loop due to the nucleation, pinning, depinning and annihilation of the vortex core.…”

Section: Modelmentioning

confidence: 79%

“…However, no internal mechanism was reported to be able to induce the change of the intermediate state, which could influence the nucleation process of the vortex. Recently, defects were intentionally incorporated in a disk, affecting the hysteresis trace drastically [26,27]. The change in hysteresis loop is usually associated with the mechanism of vortex pinning by the defects, and usually the shape of the defect investigated is circular, which involves no shape anisotropy [26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Arrangement effects of triangular defects on magnetization reversal process in a permalloy dot

Liu

2011

Journal of Magnetism and Magnetic Materials

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Vortex pinning at individual defects in magnetic nanodisks

Cited by 48 publications

References 9 publications

Magneto-optical imaging of vortex domain deformation in pinning sites

Magneto-optical imaging of vortex domain deformation in pinning sites

Magnetic vortex oscillator driven by d.c. spin-polarized current

Arrangement effects of triangular defects on magnetization reversal process in a permalloy dot

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