arXiv subjects

M. Cubukcu

Publications and source records attributed to M. Cubukcu.

13 recordsLinked to original sources

arXiv2025

Novel Magnetic Materials for Spintronic Device Technology

Spintronics, a transformative field of research, leverages the spin of electron to revolutionize electronic devices, offering significant advantages over traditional charge-based systems. This chapter highlights the critical role of novel magnetic materials in advancing spintronic technologies by addressing their fundamental properties, fabrication methods, and applications. A diverse range of materials, including ferromagnetic, antiferromagnetic, non-collinear antiferromagnetic, synthetic antiferromagnetic, ferrimagnetic, and multiferroic systems, is explored for their unique contributions to spintronic devices. Advanced fabrication techniques, such as bulk crystal formation, thin-film deposition, and nano-structuring, are detailed along characterization methods including spin-orbit torque analysis and magnetization dynamics studies. Emerging research on three-dimensional spin textures, domain walls, skyrmions, and magnons highlighted for its potential for novel spintronic applications. Additionally, the chapter reviews applications in memory technologies, spintronic nano-oscillators, and neuromorphic computing. Finally, it concludes by examining future research directions, challenges, and opportunities in spintronics, providing insights into breakthroughs that are shaping the future of this rapidly evolving field.

cond-mat.mtrl-sci↗

arXiv2024

Tunable Ultra-Strong Magnon-Magnon Coupling Approaching the Deep-Strong Regime in a van der Waals Antiferromagnet

Antiferromagnetic (AFM) magnons in van der Waals (vdW) materials offer substantial potential for applications in magnonics and spintronics. In this study, we demonstrate ultra-strong magnon-magnon coupling in the GHz regime within a vdW AFM, achieving a maximum coupling rate of 0.91. Our investigation shows the tunability of coupling strength through temperature-dependent magnetic anisotropies. We compare coupling strength values derived from the gap size from the measured spectrum with those calculated directly through the coupling parameter and show that the gap size as a measure of coupling strength is limited for the ultra-strong coupling regime. Additionally, analytical calculations show the possibility to reach the deep-strong coupling regime by engineering the magnetic anisotropy. These findings highlight the potential of vdW AFMs as a model case to study magnetisation dynamics in low-symmetry magnetic materials.

cond-mat.mes-hall↗

arXiv2021

Manipulation of magnetic skyrmions in continuous Ir/Co/Pt multilayers

We show that magnetic skyrmions can be stabilized at room temperature in continuous Ir/Co/Pt multilayers on SiO2/Si substrate without prior application of electric current or magnetic field. While decreasing the Co thickness, tuning of the magnetic anisotropy gives rise to a transition from worm-like domain patterns to long and separate stripes. The skyrmions are clearly imaged in both states using Magnetic Force Microscopy. The density of skyrmions can be significantly enhanced after applying the in-plane field procedure. In addition, we have investigated the phase diagram of a sample deposited in the same run, but onto a SiNx membrane using Lorentz transmission electron microscopy. Interestingly, this sample shows a different behaviour as function of magnetic field hinting to the influence of strain on the phase diagram of skyrmions in thin film multilayers. Our results provide means to manipulate skyrmion, further allowing for optimized engineering of skyrmion-based devices.

cond-mat.mtrl-sci↗

arXiv2021

Tailoring interfacial effect in multilayers with Dzyaloshinskii-Moriya interaction by helium ion irradiation

We show a method to control magnetic interfacial effects in multilayers with Dzyaloshinskii-Moriya interaction (DMI) using helium (He$^{+}$) ion irradiation. We report results from SQUID magnetometry, ferromagnetic resonance as well as Brillouin light scattering results on multilayers with DMI as a function of irradiation fluence to study the effect of irradiation on the magnetic properties of the multilayers. Our results show clear evidence of the He$^{+}$ irradiation effects on the magnetic properties which is consistent with interface modification due to the effects of the He$^{+}$ irradiation. This external degree of freedom offers promising perspectives to further improve the control of magnetic skyrmions in multilayers, that could push them towards integration in future technologies.

cond-mat.mtrl-sci↗

arXiv2019

Spin transport parameters of NbN thin films characterised by spin pumping experiments

We present measurements of ferromagnetic-resonance - driven spin pumping and inverse spin-Hall effect in NbN/Y3Fe5O12 (YIG) bilayers. A clear enhancement of the (effective) Gilbert damping constant of the thin-film YIG was observed due to the presence of the NbN spin sink. By varying the NbN thickness and employing spin-diffusion theory, we have estimated the room temperature values of the spin diffusion length and the spin Hall angle in NbN to be 14 nm and -1.1 10-2, respectively. Furthermore, we have determined the spin-mixing conductance of the NbN/YIG interface to be 10 nm-2. The experimental quantification of these spin transport parameters is an important step towards the development of superconducting spintronic devices involving NbN thin films.

cond-mat.mtrl-sci↗

arXiv2018

Near-field magneto-caloritronic nanoscopy on ferromagnetic nanostructures

Near-field optical microscopy by means of infrared photocurrent mapping has rapidly developed in recent years. In this letter we introduce a near-field induced contrast mechanism arising when a conducting surface, exhibiting a magnetic moment, is exposed to a nanoscale heat source. The magneto-caloritronic response of the sample to near-field excitation of a localized thermal gradient leads to a contrast determined by the local state of magnetization. By comparing the measured electric response of a magnetic reference sample with numerical simulations we derive an estimate of the field enhancement and the corresponding temperature profile induced on the sample surface.

cond-mat.mes-hall↗

arXiv2016

Disruptive effect of Dzyaloshinskii-Moriya interaction on the MRAM cell performance

In order to increase the thermal stability of a magnetic random access memory (MRAM) cell, materials with high spin-orbit interaction are often introduced in the storage layer. As a side effect, a strong Dzyaloshinskii-Moriya interaction (DMI) may arise in such systems. Here we investigate the impact of DMI on the magnetic cell performance, using micromagnetic simulations. We find that DMI strongly promotes non-uniform magnetization states and non-uniform switching modes of the magnetic layer. It appears to be detrimental for both the thermal stability of the cell and its switching current, leading to considerable deterioration of the cell performance even for a moderate DMI amplitude.

cond-mat.mes-hall↗

arXiv2015

A Dzyaloshinskii-Moriya Anisotropy in Nanomagnets with in-plane Magnetization

We report on a new source of in-plane anisotropy in nanomagnets due to the presence of Dzyaloshinskii-Moriya interaction (DMI). This anisotropy depends on the shape of the magnet, and is orthogonal to the demagnetization shape anisotropy. This effect originates from the DMI energy reduction due to an out-of-plane tilt of the spins at edges oriented perpendicular to the magnetization. Our investigation combining experimental, numerical and analytical results demonstrate that this energy reduction can compensate the demagnetization shape anisotropy energy in magnets of elongated shape, provided that their volumes is small enough and thus that their magnetization is quasi-uniform.

cond-mat.mes-hall↗

arXiv2013

Spin Pumping and Inverse Spin Hall Effect in Germanium

We have measured the inverse spin Hall effect (ISHE) in \textit{n}-Ge at room temperature. The spin current in germanium was generated by spin pumping from a CoFeB/MgO magnetic tunnel junction in order to prevent the impedance mismatch issue. A clear electromotive force was measured in Ge at the ferromagnetic resonance of CoFeB. The same study was then carried out on several test samples, in particular we have investigated the influence of the MgO tunnel barrier and sample annealing on the ISHE signal. First, the reference CoFeB/MgO bilayer grown on SiO$_{2}$ exhibits a clear electromotive force due to anisotropic magnetoresistance and anomalous Hall effect which is dominated by an asymmetric contribution with respect to the resonance field. We also found that the MgO tunnel barrier is essential to observe ISHE in Ge and that sample annealing systematically lead to an increase of the signal. We propose a theoretical model based on the presence of localized states at the interface between the MgO tunnel barrier and Ge to account for these observations. Finally, all of our results are fully consistent with the observation of ISHE in heavily doped $n$-Ge and we could estimate the spin Hall angle at room temperature to be $\approx$0.001.

cond-mat.mtrl-sci↗

arXiv2013

Crossover from spin accumulation into interface states to spin injection in the germanium conduction band

Electrical spin injection into semiconductors paves the way for exploring new phenomena in the area of spin physics and new generations of spintronic devices. However the exact role of interface states in spin injection mechanism from a magnetic tunnel junction into a semiconductor is still under debate. In this letter, we demonstrate a clear transition from spin accumulation into interface states to spin injection in the conduction band of $n$-Ge. We observe spin signal amplification at low temperature due to spin accumulation into interface states followed by a clear transition towards spin injection in the conduction band from 200 K up to room temperature. In this regime, the spin signal is reduced down to a value compatible with spin diffusion model. More interestingly, we demonstrate in this regime a significant modulation of the spin signal by spin pumping generated by ferromagnetic resonance and also by applying a back-gate voltage which are clear manifestations of spin current and accumulation in the germanium conduction band.

cond-mat.mtrl-sci↗

arXiv2010

Effect of picosecond strain pulses on thin layers of the ferromagnetic semiconductor (Ga,Mn)(As,P)

The effect of picosecond acoustic strain pulses (ps-ASP) on a thin layer of (Ga,Mn)As co-doped with phosphorus was probed using magneto-optical Kerr effect (MOKE). A transient MOKE signal followed by low amplitude oscillations was evidenced, with a strong dependence on applied magnetic field, temperature and ps-ASP amplitude. Careful interferometric measurement of the layer's thickness variation induced by the ps-ASP allowed us to model very accurately the resulting signal, and interpret it as the strain modulated reflectivity (differing for $σ_{\pm}$ probe polarizations), independently from dynamic magnetization effects.

cond-mat.mtrl-sci↗

arXiv2009

Phosphorous alloying: controlling the magnetic anisotropy in ferromagnetic (Ga,Mn)(As,P) Layers

Phosphorous alloying of GaMnAs thin films has been used for the manipulation of the magnetic anisotropies in ferromagnetic Ga0.93Mn0.07As1-yPy layers. We have determined the anisotropy constants as a function of temperature for phosphorous alloying levels between 0 and 8.8 at % for a Mn doping level of ~ 7at%. We show that it is possible to obtain layers with robust ferromagnetism and either in-plane or out-of plane easy axes with small barriers for magnetization reorientation by phosphorous alloying with y< 6at% or y> 6at%. The critical temperatures are not significantly increased by the P alloying.

cond-mat.mtrl-sci↗

arXiv2008

Damping and magnetic anisotropy of ferromagnetic GaMnAs thin films

The magnetic properties of annealed, epitaxial Ga0.93Mn0.07As layers under tensile and compressive stress have been investigated by X-band (9GHz) and Q-band (35GHz) ferromagnetic resonance (FMR) spectroscopy. From the analysis of the linewidths of the uniform mode spectra the FMR Gilbert damping factor "alpha" has been determined. At T=4K we obtain a minimum damping factor of "alpha" = 0.003 for the compressively stressed layer. Its value is not isotropic. It has a minimum value for the easy axes orientations of the magnetic field and increases with the measuring temperature. Its average value is for both type of films of the order of 0.01 in spite of strong differences in the inhomogeneous linewidth which vary between 20 Oe and 600 Oe for the layers grown on GaAs and GaInAs substrates respectively.

cond-mat.mtrl-sci↗