Muhammad Asif Bashir

Measuring broadband magnetic fields on the nanoscale using a hybrid quantum register

The generation and control of fast switchable magnetic fields with large gradients on the nanoscale is of fundamental interest in material science and for a wide range of applications. However, it has not yet been possible to characterize those fields at high bandwidth with arbitrary orientations. Here, we measure the magnetic field generated by a hard-disk-drive write head with high spatial resolution and large bandwidth by coherent control of single electron and nuclear spins. We are able to derive field profiles from coherent spin Rabi oscillations close to the gigahertz range, measure magnetic field gradients on the order of 1 mT nm-1 and quantify axial and radial components of a static and dynamic magnetic field independent of its orientation. Our method paves the way for precision measurement of the magnetic fields of nanoscale write heads, which is important for future miniaturization of these devices.The generation and control of nanoscale magnetic fields are of fundamental interest in material science and a wide range of applications. Nanoscale magnetic resonance imaging quantum spintronics for example require single spin control with high precision and nanoscale spatial resolution using fast switchable magnetic fields with large gradients. Yet, characterizing those fields on nanometer length scales at high band width with arbitrary orientation has not been possible so far. Here we demonstrate single electron and nuclear spin coherent control using the magnetic field of a hard disc drive write head. We use single electron spins for measuring fields with high spatial resolution and single nuclear spins for large band width measurements. We are able to derive field profiles from coherent spin Rabi oscillations close to GHz in fields with gradients of up to 10 mT/nm and measure all components of a static and dynamic magnetic field independent of its orientation. Our method paves the way for precision measurement of the magnetic fields of nanoscale write heads important for future miniaturization of the devices.

Dynamic Field Gradient and Erasure After Write for High Data Rate Recording

Extensive micromagnetic simulations are performed to investigate the impact of the current overshoot amplitude (OSA) on the writer dynamics. The field risetime, dynamic gradient, bubble width, as well as erasure risk due to large stray fields in the neighbouring tracks during the switching are all shown to be very sensitive to the OSA. Numerical results show that increasing OSA can sharply improve the field risetime. However, it also leads to a larger write bubble expansion during switching which could result in a wider track width and reduce track per inch (TPI) capability. The risk of side track erasure for different overshoot conditions are evaluated and also tend to increase with higher OSA. Futhermore, results for remnant fields in the media produced by the writer are shown to be extremely sensitive to the choice of damping parameter used in the simulations.

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

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 devices, as well as being relevant to other magnetic devices.

Study of Trailing Edge Shield Magnetic Properties for Writer Performance Improvement for Perpendicular Magnetic Recording

Micromagnetic modeling is used to evaluate the effect of trailing edge shield (TES) magnetic properties on the dynamic performance of a writer used in perpendicular magnetic recording with wrapped around shield at air bearing surface. The gradient of the field increased with the increase in the TES saturation flux density and thickness; however the writer bubble width and field decreased as more flux turned toward the TES. The improvement of gradient can be vital for recording as the field can be traded-off until its just above the media switching field helping form sharp transitions between bits and reduce the bit-error-rate. The reduction in the bubble width enables higher track density. Additionally, the manipulation of the anisotropy in TES can help increase the gradient further, promoted by easier flux flow.