Time resolved scanning Kerr microscopy of hard disk writer structures with a multilayered yoke

Yu, Wei; Gangmei, P.; Keatley, P. S.; Hicken, R. J.; Gubbins, M.; Czoschke, Peter; Lopusnik, R.

doi:10.1063/1.4802977

Cited by 9 publications

(4 citation statements)

References 15 publications

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“…The flexibility of TRSKM has also permitted dynamical studies of magnetic vortices [24][25][26][27][28][29], rings [30,31], domain walls [32], microwave assisted magnetic switching [33], and hard disk writers for perpendicular media disks [34][35][36]. In the last decade, emerging phenomena in spintronics have also been explored using TRSKM.…”

Section: Introductionmentioning

confidence: 99%

A platform for time-resolved scanning Kerr microscopy in the near-field

Keatley

Loughran

Hendry

et al. 2017

Review of Scientific Instruments

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Time-resolved scanning Kerr microscopy (TRSKM) is a powerful technique for the investigation of picosecond magnetization dynamics at sub-micron length scales by means of the magneto-optical Kerr effect (MOKE). The spatial resolution of conventional (focused) Kerr microscopy using a microscope objective lens is determined by the optical diffraction limit so that the nanoscale character of the magnetization dynamics is lost. Here we present a platform to overcome this limitation by means of a near-field TRSKM that incorporates an atomic force microscope (AFM) with optical access to a metallic AFM probe with a nanoscale aperture at its tip. We demonstrate the near-field capability of the instrument through the comparison of time-resolved polar Kerr images of magnetization dynamics within a microscale NiFe rectangle acquired using both near-field and focused TRSKM techniques at a wavelength of 800 nm. The flux-closure domain state of the in-plane equilibrium magnetization provided the maximum possible dynamic polar Kerr contrast across the central domain wall and enabled an assessment of the magneto-optical spatial resolution of each technique. Line profiles extracted from the Kerr images demonstrate that the near-field spatial resolution was enhanced with respect to that of the focused Kerr images. Furthermore, the near-field polar Kerr signal (∼1 mdeg) was more than half that of the focused Kerr signal, despite the potential loss of probe light due to internal reflections within the AFM tip. We have confirmed the near-field operation by exploring the influence of the tip-sample separation and have determined the spatial resolution to be ∼550 nm for an aperture with a sub-wavelength diameter of 400 nm. The spatial resolution of the near-field TRSKM was in good agreement with finite element modeling of the aperture. Large amplitude electric field along regions of the modeled aperture that lie perpendicular to the incident polarization indicate that the aperture can support plasmonic excitations. The comparable near-field and focused polar Kerr signals suggest that such plasmonic excitations may lead to an enhanced near-field MOKE. This work demonstrates that near-field TRSKM can be performed without significant diminution of the polar Kerr signal in relatively large, sub-wavelength diameter apertures, while development of a near-field AFM probe utilizing plasmonic antennas specifically designed for measurements deeper into the nanoscale is discussed.

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Section: Introductionmentioning

confidence: 99%

A platform for time-resolved scanning Kerr microscopy in the near-field

Keatley

Loughran

Hendry

et al. 2017

Review of Scientific Instruments

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“…However, during pulse cycling, the yoke can also occupy a meta-stable equilibrium state depending upon the driving pulse configuration. 13,14 The dynamic images suggest the formation a multi-domain equilibrium state. The perpendicular channel images reveal a light vertical stripe close to winding C3 up to 3.58 ns delay, after which additional black contrast appears around the stripe before quickly fading again.…”

mentioning

confidence: 99%

“…The increased availability of modelocked pulsed laser systems of improved mode profile has allowed time resolved measurements to be performed with diffraction limited spatial resolution and picosecond temporal resolution. In recent studies [12][13][14] we have shown that yokes with different coil configurations can occupy different meta-stable states during pulse cycling. Pulses of similar amplitude but opposite polarity also caused the pole tip magnetization to exhibit changes of different amplitude, suggesting a complicated influence of the yoke dynamics upon the write field.…”

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confidence: 99%

Time resolved imaging of magnetization dynamics in hard disk writer yokes excited by bipolar current pulses

Keatley

Hicken

et al. 2014

Journal of Applied Physics

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A partially built hard disk writer structure with a NiFe/CoFe/Ru/NiFe/CoFe synthetic antiferromagnetic (SAF) yoke was studied by time and vector resolved scanning Kerr microscopy. All three time dependent components of the magnetization were recorded simultaneously as a bipolar current pulse with 1 MHz repetition rate was delivered to the coil. The component of magnetization parallel to the symmetry axis of the yoke was compared at the pole and above a coil winding in the centre of the yoke. The two responses are in phase as the pulse rises, but the pole piece lags the yoke as the pulse falls. The Kerr signal is smaller within the yoke than within the confluence region during pulse cycling. This suggests funneling of flux into the confluence region. Dynamic images acquired at different time delays showed that the relaxation is faster in the centre of the yoke than in the confluence region, perhaps due to the different magnetic anisotropy in these regions. Although the SAF yoke is designed to support a single domain to aid flux conduction, no obvious flux beaming was observed, suggesting the presence of a more complicated domain structure. The SAF yoke writer hence provides relatively poor flux conduction but good control of rise time compared to single layer and multi-layered yokes studied previously.

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“…8 Previous experimental studies either have concentrated solely on the pole tip region from the perspective of the air-bearing surface 9,10 or have been unable to provide high enough spatial resolution to resolve the pole tip and confluence region. [11][12][13] A stable equilibrium state, particularly in the confluence region and pole tip, is essential for producing a reliable write field while the magnetization dynamics within the yoke can significantly alter the amplitude and temporal form of the write field. 14 In this study, writer structures with a multilayered yoke were imaged with both x-ray photoemission electron microscopy (XPEEM) and time-resolved scanning Kerr microscopy (TRSKM) to provide information about the equilibrium state of the entire writer structure and the dynamic response of the yoke, respectively.…”

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Imaging the equilibrium state and magnetization dynamics of partially built hard disk write heads

Valkass

Shelford

et al. 2015

Applied Physics Letters

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Four different designs of partially built hard disk write heads with a yoke comprising four repeats of NiFe (1 nm)/CoFe (50 nm) were studied by both x-ray photoemission electron microscopy (XPEEM) and time-resolved scanning Kerr microscopy (TRSKM). These techniques were used to investigate the static equilibrium domain configuration and the magnetodynamic response across the entire structure, respectively. Simulations and previous TRSKM studies have made proposals for the equilibrium domain configuration of similar structures, but no direct observation of the equilibrium state of the writers has yet been made. In this study, static XPEEM images of the equilibrium state of writer structures were acquired using x-ray magnetic circular dichroism as the contrast mechanism. These images suggest that the crystalline anisotropy dominates the equilibrium state domain configuration, but competition with shape anisotropy ultimately determines the stability of the equilibrium state. Dynamic TRSKM images were acquired from nominally identical devices. These images suggest that a longer confluence region may hinder flux conduction from the yoke into the pole tip: the shorter confluence region exhibits clear flux beaming along the symmetry axis, whereas the longer confluence region causes flux to conduct along one edge of the writer. The observed variations in dynamic response agree well with the differences in the equilibrium magnetization configuration visible in the XPEEM images, confirming that minor variations in the geometric design of the writer structure can have significant effects on the process of flux beaming.

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Time resolved scanning Kerr microscopy of hard disk writer structures with a multilayered yoke

Abstract: Erratum: "Time resolved scanning Kerr microscopy of hard disk writer structures with a multilayered yoke" [Appl.

Cited by 9 publications

References 15 publications

A platform for time-resolved scanning Kerr microscopy in the near-field

A platform for time-resolved scanning Kerr microscopy in the near-field

Time resolved imaging of magnetization dynamics in hard disk writer yokes excited by bipolar current pulses

Imaging the equilibrium state and magnetization dynamics of partially built hard disk write heads

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