Kyung-Won Chung

Engineered superparamagnetic Mn0.5Zn0.5Fe2O4 nanoparticles as a heat shock protein induction agent for ocular neuroprotection in glaucoma

Ocular neuroprotection induced by localized heat shock proteins (HSPs) has been paid considerable attention as an efficacious treatment modality for glaucoma. However, the current clinical approaches to induce HSPs in the retinal ganglion cells (RGCs) are limited due to undesirable side effects. Here, we present that the induction of HSPs by local magnetic hyperthermia using engineered superparamagnetic Mn(0.5)Zn(0.5)Fe(2)O(4) nanoparticle agents (EMZF-SPNPAs) with a 5.5 nm mean particle size is promisingly feasible for a physiologically tolerable ocular neuroprotection modality. The sufficiently high specific absorption rate (SAR) (∼256.4 W/g in an agar solution) achieved at the biologically safe range of applied AC magnetic field and frequency as well as the superior biocompatibility of EMZF-SPNPA, which were confirmed from both in-vitro and in-vivo animal pilot studies, allowing it to be considered as a potential localized HSPs agent. Furthermore, the successful demonstration of a newly designed infusion technique, which diffuses the EMZF-SPNPAs through the vitreous body to the retina in a rat eye, more strongly verified the promises of this biotechnical approach to the ocular neuroprotection modality in glaucoma clinics.

Numerical simulation of current density induced magnetic failure for giant magnetoresistance spin valve read sensors

It was numerically demonstrated that current-in-plane (CIP) and current-perpendicular-to-plane (CPP) Ir20Mn80 based giant magnetoresistance spin valve read sensors operating at an extremely high current density (J≥1×108 A/cm2) show completely different electrical and magnetic failure mechanisms: (1) CIP read sensors, electromigration-induced Cu spacer diffusion and correspondingly degraded interlayer coupling were primarily responsible for the failures; while, (2) CPP read sensors, the deterioration of exchange bias due to thermomigration-induced Mn interdiffusion at the Co80Fe20/Ir20Mn80 interface was found to be dominant. The different temperature and current distribution resulting in different mass-transport mechanisms are the main physical reasons for the failure.

Thermomigration-induced magnetic degradation of current perpendicular to the plane giant magnetoresistance spin-valve read sensors operating at high current density

The theoretically analyzed physical mechanism of thermomigration (TM)-induced magnetic degradation that occurred in the current perpendicular to the plane (CPP) Ir20Mn80 exchange biased giant magnetoresistance spin-valve (EBGMR SV) read sensors is presented. The device size was changed from 60×60 to 140×140 nm2 at the fixed aspect ratio of 1(L):1(W), and the operating current density was varied from J=1×108 A/cm2 to J=5×108 A/cm2 in a current control mode. It was numerically confirmed that the Mn atomic interdiffusion through the Ir20Mn80/Co80Fe20 interface due to the thermally induced mass transport and the “Villari magnetic reversal” of the CoFe pinned layer due to the thermally induced stress are mainly responsible for the serious degradation of exchange bias and magnetoresistance. Furthermore, the TM-induced magnetic degradation of CPP EBGMR SV read sensors was found to become severe by increasing the operating current density. However, interestingly, this undesirable magnetic degradation was dramatic...

Numerical failure analysis of current-confined-path current perpendicular-to-plane giant magnetoresistance spin-valve read sensors under high current density

Thermomigration (TM)-induced failures occurred in the current-confined-path (CCP) current perpendicular-to-the plane (CPP) giant magnetoresistance spin valve (GMR SV) read sensors with Cu nanopillar metal paths (∼5 nm in diameter) operating at a high current density (J>2×107 A/cm2) have been numerically studied to explore the magnetic and electrical stability. The Cu interdiffusion (migration) from nanopillars into adjacent magnetic layers (e.g., CoFe) due to thermally induced mass transport was found to be the main physical reason for the magnetic failures of CCP-CPP GMR SV read sensors including the change in interlayer coupling and the reduction in exchange bias field as well as MR. Furthermore, it was numerically verified that the TM-induced failures are more dominant than the electromigration-induced failures at the higher current density beyond J=6×107 A/cm2 in the CCP-CPP GMR SV read sensors. However, all the numerical calculation results demonstrated in this study clearly suggest that these undesi...

Hall effect-induced acceleration of electromigration failures in spin valve multilayers under magnetic field

It was observed that electromigration (EM)-induced failures in spin valve multilayers were severely accelerated by an externally applied magnetic field. The theoretical and experimental analysis results confirmed that Hall effect-induced Lorentz force applied to the perpendicular-to-the-film-plane direction is primarily responsible for the severe acceleration of the EM failures due to its dominant contribution to abruptly increasing local temperature and current density. The proposed failure model and the theoretical calculations were demonstrated to agree well with the experimental observations.

Effects of media stray field on electromigration characteristics in current-perpendicular-to-plane giant magnetoresistance spin-valve read sensors

Effects of magnetic stray field retrieved from both longitudinal and perpendicular magnetic recording media (denoted by “media stray field”) on electromigration (EM) characteristics of current-perpendicular-to-plane (CPP) giant magnetoresistance spin-valve (GMR SV) read sensors have been numerically studied to explore the electrical and magnetic stability of the read sensor under real operation. The mean-time-to-failure (MTTF) of the CPP GMR SV read sensors was found to have a strong dependence on the physical parameters of the recording media and recorded information status, such as the pulse width of media stray field, the bit length, and the head moving velocity. According to the numerical calculation results, it was confirmed that in the longitudinal media, the shorter the stray field pulse width (i.e., the sharper the media transition) allows for the longer MTTF of the CPP GMR SV read sensors; while in the perpendicular media, the sharper the media transition gives rise to a shorter MTTF. Interesting...

Electromigration in Giant Magnetoresistance Spin Valve Read Sensors Under Pulsed DC Magnetic Field: An Analytical and Numerical Study

A theoretical model is proposed to investigate the electromigration (EM) behavior in giant magnetoresistance spin valve (GMR SV) read sensors under pulsed direct current (dc) magnetic field during sensor operation. It was found that the externally applied magnetic field gives rise to a more severe Joule heating and consequently raises the device temperature leading to EM acceleration. Blacks equation was modified based on Greens function method and the Boltzmann equation to more precisely interpret the EM mean time to failure (MTTF) of GMR SV read sensors under pulsed dc magnetic field. The physical validity of this proposed model was confirmed by the comparisons with experimental results.