Thickness dependent magnetization states of Fe islands on W(110): From single domain to vortex and diamond patterns

Bode, Matthias; Wachowiak, Andre; Wiebe, Jens; Kubetzka, André; Morgenstern, Markus; Wiesendanger, R.

doi:10.1063/1.1644613

Cited by 68 publications

(36 citation statements)

References 14 publications

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“…Fig. 3 (a) layer's reduced thickness, which makes the vortex state energetically unfavorable 21 . As H ll increases from zero the differential resistance decreases gradually as the vortex core approaches the device boundary.…”

Section: Pribiag Et Almentioning

confidence: 99%

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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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Section: Pribiag Et Almentioning

confidence: 99%

“…The thickness of the 60 nm Py layer is chosen to be above the threshold thickness necessary for the nucleation of a magnetic vortex 21 . Electronbeam lithography and ion milling were used to define and etch the spin valves resulting in pillar-shaped devices with 160 nm x 75 nm elliptical cross-section (Fig.…”

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confidence: 99%

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

et al. 2007

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“…13 This growth mode continues to about 2 ML, 32 but, at higher coverage, Stranski-Krastanov growth occurs, with large Fe islands being formed at least ten atomic layers thick on a pseudomorphic Fe monolayer. 33 Capping such Fe stripes and layers with Au at room temperature does not produce any interdiffusion or reaction. 16 The upper left panels of Figs.…”

Section: Resultsmentioning

confidence: 99%

Temperature-dependent magnetic second-harmonic generation from Fe nanostructures grown on vicinal W(110)

et al. 2011

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Temperature-dependent magnetic second-harmonic generation (MSHG) at normal incidence (NI) is used to determine magnetization curves from Au-capped ultrathin Fe nanostructures grown on a vicinal W(110) substrate. Aligned magnetic nanostructures grown on low-symmetry interfaces are generally inhomogeneous, with different magnetic species, such as terrace and step atoms, contributing to the overall magnetic response from the interfacial regions. A phenomenological model of NI MSHG intensity and contrast at magnetic interfaces of 1 m symmetry is used to extract the magnetization information. Two characteristic temperatures are identified for both 0.75 and 2.0 monolayers of Fe, and it is proposed that the increased sensitivity of SHG to step atoms, compared to linear optical techniques, allows the contribution of boundary atoms to the spin block response to be directly detected at lower temperatures. The behavior of boundary spins such as these is expected to be important for atomic-scale magnetic structures.

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“…For Fe deposition on °4 This growth mode continues to about 2 ML [28] but, at higher coverage, Stranski-Krastanov growth occurs, with large Fe islands being formed, at least ten atomic layers thick, on a pseudomorphic Fe monolayer [29]. In addition, it is well established that capping such Fe layers with Au at room temperature does not produce any inter-diffusion or reaction [3].…”

Section: Hysteresis Loops and Curie Curves From Au-capped Fe Nanostrumentioning

confidence: 93%

Magnetic second-harmonic generation from interfaces and nanostructures

McGilp

Carroll

Fleischer

et al. 2010

Journal of Magnetism and Magnetic Materials

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Magneto-optic techniques provide non-contact and non-destructive characterization of magnetic materials. This includes embedded magnetic nanostructures, which are accessible due to the large penetration depth of optical radiation. The linear magneto-optic Kerr effect is widely used in the growth and characterization of ultra-thin magnetic films and can show monolayer sensitivity. Nonlinear magnetic second-harmonic generation (MSHG) is a more difficult and expensive technique but, uniquely, can measure the surface and interface magnetism of centrosymmetric magnetic films with sub-monolayer sensitivity. MSHG is briefly reviewed and examples from high symmetry interfaces and nanostructures described. Low symmetry structures are more difficult to characterize, however, because of the large number of tensor components that may contribute to the signal. An important class of low symmetry systems exploits vicinal substrates to grow aligned magnetic nanostructures by self-organization. These structures have a high proportion of magnetic step or edge atoms relative to the terrace atoms, and the overall magnetic response is expected to contain significant contributions from these different magnetic regions. It is shown that contributions from these different regions can be identified using normal A c c e p t e d m a n u s c r i p t -2 -incidence (NI) MSHG. This new approach is used to determine hysteresis loops from Au-capped Fe monolayers grown on a vicinal W(110) substrate. Temperature-dependent studies of the MSHG contrast also allow Curie temperatures to be determined. This experimental procedure and phenomenology opens up low symmetry magnetic interfaces and aligned nanostructures to characterization by MSHG.

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Thickness dependent magnetization states of Fe islands on W(110): From single domain to vortex and diamond patterns

Cited by 68 publications

References 14 publications

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

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

Temperature-dependent magnetic second-harmonic generation from Fe nanostructures grown on vicinal W(110)

Magnetic second-harmonic generation from interfaces and nanostructures

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