arXiv subjects

M. R. Hajiali

Publications and source records attributed to M. R. Hajiali.

5 recordsLinked to original sources

arXiv2020

Coexistence of exchange bias training effect and spin-orbit torque in IrMn-layer/ferromagnetic-ribbon heterostructures via magnetoimpedance effect

We investigate a possible correlation between spin orbit torque (SOT) and exchange-bias (EB) in IrMn-layer/ferromagnetic-ribbon heterostructure by performing magnetoimpedance (MI) measurements. To uncover this correlation, we benefit from EB training effect probed by MI effect at room temperature. A damping-like SOT driven by ac current through the antiferromagnetic IrMn applies to the ferromagnetic ribbon layer, determined by MI magnetic field and frequency sweeps. Importantly, magnitude of the SOT is observed to remain intact against EB training and decrease of EB through alternative magnetic field sweep cycles. Our results pave the way to better elucidate the EB effect, EB training and the SOT, useful for future spintronic elements.

cond-mat.mes-hall↗

arXiv2019

Controlling Magnetization of Gr/Ni Composite for Application in High Performance Magnetic Sensors

Graphene (Gr), a well-known 2D material, has been under intensive investigation in the last decade due to its high potential applications in industry and advanced technological elements. The Gr, while composed with magnetic materials, has opened new opportunities for further developments of magnetic based devices. Here, we report a mass production of Gr/Ni composite powders using electrochemical exfoliation/deposition method with different magnetic strengths of the final composite material. We applied the magnetic composite materials in a magnetoimpedance (MI) based sensor and observed significant enhancement in the MI effect and its field sensitivity. Such magnetic composites with controlled magnetization strengths are coated on the MI-ribbon sensor surface and different MI responses are observed. The MI response of a ribbon coated with a Gr/Ni layer is theoretically determined based on an electrodynamic model with a qualitative consistency between the experimental results and the theoretical model. Our comprehensive study can be applied in high performance functionalized MI based magnetic sensors and devices.

physics.app-ph↗

arXiv2018

Effect of sputter deposited ZnO thin layers on magnetoimpedance response and field sensitivity of Co-based micro-wires

Semiconductive ZnO has shown to be a fascinating element for application in high-performance sensors. ZnO with various thicknesses (87-500 nm) was deposited on the surface of Co-based amorphous micro-wire (Co68.15Fe4.35Si12.5B15) using magnetron sputtering technique and the magnetoimpedance (MI) response was evaluated. The MI% increases monotonously up to the 240 nm thickness of the ZnO layer. By further increase in the ZnO layer thickness the MI% decreases. MI response and field sensitivity increased from 227% and 1.7 %/Oe for bare micro-wire up to 406% and 4.99 %/Oe for ZnO deposited micro-wire with a thickness of 240 nm. The x-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the structural grown ZnO layers. Vibrating sample magnetometry (VSM) was used to reveal the role of the ZnO thin layer in the MI response. The same trend of increase and decrease in the MI% by thickness was observed for the transverse permeability of the samples determined by VSM. The obtained results address a simple way to achieve high MI response and sensitivity with selective surface sensing.

physics.app-ph↗

arXiv2017

Spin-orbit-torque driven magnetoimpedance in Pt-layer/magnetic-ribbon heterostructures

When a flow of electron passes through a paramagnetic layer with strong spin-orbit-coupling such as platinum (Pt), a net spin current is produced via spin Hall effect (SHE). This spin current can exert a torque on the magnetization of an adjacent ferromagnetic layer which can be probed via magnetization dynamic response, e.g. spin-torque ferromagnetic resonance (ST-FMR). Nevertheless, that effect in lower frequency magnetization dynamic regime (MHz) where skin effect occurs in high permeability ferromagnetic conductors namely the magneto-impedance (MI) effect can be fundamentally important which has not been studied so far. Here, by utilizing the MI effect in magnetic-ribbon/Pt heterostructure with high magnetic permeability that allows the ac current effectively confined at the skin depth of ~100 nm thickness, the effect of spin-orbit-torque (SOT) induced by the SHE probed via MI measurement is investigated. We observed a systematic MI frequency shift that increases by increasing the applied current amplitude and thickness of the Pt layer (varying from 0 nm to 20 nm). In addition, the role of Pt layer in ribbon/Pt heterostructure is evaluated with ferromagnetic resonance (FMR) effect representing standard Gilbert damping increase as the result of presence of the SHE. Our results unveil the role of SOT in dynamic control of the transverse magnetic permeability probed with impedance spectroscopy as useful and valuable technique for detection of future SHE devices.

cond-mat.mes-hall↗

arXiv2017

Current driven second harmonic domain wall resonance in ferromagnetic metal/ nonmagnetic metal bilayer: a field-free method for spin Hall angle measurements

We study the ac current-driven domain wall motion in bilayer ferromagnetic metal (FM)/nonmagnetic metal (NM) nanowire. The solution of the modified Landau-Lifshitz-Gilbert equation including all the spin transfer torques is used to describe motion of the domain wall in presence of the spin Hall effect. We show that the domain wall center has second harmonic frequency response in addition to the known first harmonic excitation. In contrast to the experimentally observed second harmonic response in harmonic Hall measurements of spin-orbit torque in magnetic thin films, this second harmonic response directly originates from spin-orbit torque driven domain wall dynamics. Based on the spin current generated by domain wall dynamics, the longitudinal spin motive force generated voltage across the length of the nanowire is determined. The second harmonic response introduces additionally a new practical field-free and all-electrical method to probe the effective spin Hall angle for FM/NM bilayer structures that could be applied in experiments. Our results also demonstrate the capability of utilizing FM/NM bilayer structure in domain wall based spin torque signal generators and resonators.

cond-mat.mes-hall↗