Time-resolved scanning Kerr microscopy of flux beam formation in hard disk write heads

Valkass, R. A. J.; Spicer, Timothy; Burgos-Parra, Erick; Hicken, R. J.; Bashir, Muhammad; Gubbins, M.; Czoschke, Peter; Lopusnik, R.

doi:10.1063/1.4954018

Cited by 5 publications

(3 citation statements)

References 18 publications

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“…With regard to magnetic recording, we note that industrial heads have a high saturation induction of 1.8–2.2 T due to the use of FeCo alloy [ 2 , 67 , 68 , 69 ], whereas our alloy free of expensive cobalt has the comparable induction in weaker magnetic fields. This realizes efficient operation with a lower amperage, a smaller cross-section of electrical conductor, and a smaller number of magnetizing winding turns, which allow one to reduce the size and weight of devices while maintaining their operational characteristics.…”

Section: Discussionmentioning

confidence: 99%

FeZrN Films: Magnetic and Mechanical Properties Relative to the Phase-Structural State

et al. 2021

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The paper presents results of investigation of Fe65.3–100Zr34.7–0N7.5–0 films prepared by dc magnetron deposition on glass substrates and subsequent 1-hour annealing at temperatures of 300–600 °C. The influence of the chemical and phase compositions and structure of the films, which were studied by TEM, SEM, XRD, and GDOES, on their mechanical properties determined by nanoindentation and static magnetic properties measured by VSM method is analyzed. The studied films exhibit the hardness within a range of 14–21 GPa, low elastic modulus (the value can reach 156 Gpa), and an elastic recovery of 55–83%. It was shown that the films are strong ferromagnets with the high saturation induction Bs (up to 2.1 T) and low coercive field Hc (as low as 40 A/m). The correlations between the magnetic and mechanical properties, on one hand, and the chemical composition of the films, their phase, and structural states as well, on the other hand, are discussed.

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Section: Discussionmentioning

confidence: 99%

FeZrN Films: Magnetic and Mechanical Properties Relative to the Phase-Structural State

et al. 2021

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“…Here time resolved scanning Kerr microscopy (TRSKM) [20][21][22][23] is used to study NC-SHNO devices. The response to both a radio frequency (RF) current I RF , and a DC current I DC when phase-locked to an injected I RF , are observed.…”

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confidence: 99%

“…The inductive and capacitative arms were used to supply I DC and I RF respectively, while the RF signal from the device was directed into a spectrum analyzer via a circulator and +24 dB pre-amplifier. Stroboscopic TRSKM measurements were performed with a vector quadrant bridge detector that exploits different magneto optical Kerr effect (MOKE) geometries to simultaneously detect the three spatial components of the dynamic magnetization and the optical reflectance 24 . The dynamics must be synchronized, via the injected I RF , to an exact multiple of the 80 MHz repetition rate of the laser within the TRSKM.…”

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confidence: 99%

Time resolved imaging of the non-linear bullet mode within an injection-locked nano-contact spin Hall nano-oscillator

Spicer

Keatley

Dvornik

et al. 2018

Applied Physics Letters

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Time-resolved scanning Kerr microscopy (TRSKM) has been used to image precessional magnetization dynamics excited by a DC current within a nano-contact (NC) spin Hall nano-oscillator (SHNO). Injection of a radio frequency (RF) current was used to phase lock the SHNO to the TRSKM. The out of plane magnetization was detected by means of the polar magneto optical Kerr effect (MOKE). However, longitudinal MOKE images were dominated by an artifact arising from the edges of the Au NCs. Time resolved imaging revealed the simultaneous excitation of a non-linear 'bullet' mode at the centre of the device, once the DC current exceeded a threshold value, and ferromagnetic resonance (FMR) induced by the RF current. However, the FMR response observed for sub-critical DC current values exhibits an amplitude minimum at the centre, which is attributed to spreading of the RF spin current due to the reactance of the device structure. This FMR response can be subtracted to yield images of the bullet mode. As the DC current is increased above threshold, the bullet mode appears to increase in size, suggesting increased translational motion. The reduced spatial overlap of the bullet and FMR modes, and this putative translational motion, may impede the injection locking and contribute to the reduced locking range observed within NC-SHNO devices. This illustrates a more general need to control the geometry of an injection-locked oscillator so that the autonomous dynamics of the oscillator exhibit strong spatial overlap with those resulting from the injected signal.Within a spin torque oscillator (STO), magnetic autooscillations, with MHz to GHz frequencies, are driven by the spin transfer torque (STT) associated with injection of DC spin current. Their frequency and amplitude can be tuned via either the DC electrical bias current or an applied magnetic field, while the magnetoresistance of the constituent materials leads to the generation of voltage oscillations. STOs have strong potential for magnetic sensing, signal processing, and neurmorphic computing applications 1,2 . The ability to lock the frequency and phase of the STO to an injected RF signal is an important property within applications, while arrays of STOs promise increased output power through mutual synchronization. However it is first necessary to understand the character of the underlying magnetization dynamics. More specifically, the dynamics excited by both DC and RF currents must be determined if the conditions required for phase-locking are to be fully understood.Within a spin Hall nano-oscillator (SHNO) the Spin Hall effect (SHE) 3,4 drives a pure spin current from a heavy metal with large spin-orbit interaction into a ferromagnet layer 5-7 . The de-coupling of charge and spin currents opens up new device geometries, for example enabling exploitation of magnetic insulators 8 , and in the present study, allows optical access to the active region of the device.The generation of magnetic auto-oscillations requires a critical spin current density to be exceeded. Within t...

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Time-resolved scanning Kerr microscopy of flux beam formation in hard disk write heads

Valkass

Spicer

Burgos-Parra

et al. 2016

Journal of Applied Physics

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To meet growing data storage needs, the density of data stored on hard disk drives must increase. In pursuit of this aim the magnetodynamics of the hard disk write head must be characterized and understood, particularly the process of "flux beaming". In this study, seven different configurations of perpendicular magnetic recording (PMR) write heads were imaged using time-resolved scanning Kerr microscopy, revealing their detailed dynamic magnetic state during the write process. It was found that the precise position and number of driving coils can significantly alter the formation of flux beams during the write process. These results are applicable to the design and understanding of current PMR and next-generation heat-assisted magnetic recording (HAMR) devices, as well as being relevant to other magnetic devices. a) Corresponding author. rajv202@ex.ac.uk

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Time-resolved scanning Kerr microscopy of flux beam formation in hard disk write heads

Cited by 5 publications

References 18 publications

FeZrN Films: Magnetic and Mechanical Properties Relative to the Phase-Structural State

FeZrN Films: Magnetic and Mechanical Properties Relative to the Phase-Structural State

Time resolved imaging of the non-linear bullet mode within an injection-locked nano-contact spin Hall nano-oscillator

Time-resolved scanning Kerr microscopy of flux beam formation in hard disk write heads

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