Evangelos Th. Papaioannou

Evangelos Th. Papaioannou
Aristotle University of Thessaloniki | AUTH · Department of Applied and Environmental Physics

Professor
Materials science, magnetic nanostructures, THz spintronic emitters, spintronics, antiferromagnetic multilayers

About

120
Publications
17,443
Reads
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2,683
Citations
Additional affiliations
January 2020 - August 2023
Martin Luther University Halle-Wittenberg
Position
  • Researcher
June 2012 - January 2020
RPTU - Rheinland-Pfälzische Technische Universität Kaiserslautern Landau
Position
  • Professor
January 2008 - May 2012
Uppsala University
Position
  • Researcher
Education
July 2002 - July 2006

Publications

Publications (120)
Article
Full-text available
Perpendicular magnetic anisotropy at transition metal/oxide interfaces plays a significant role in technological applications such as magnetic storage and spintronics. In this study, we investigate the effects of thermal annealing and Pt ultrathin interlayers on the magnetic anisotropy in Ni/NiO multilayers. Ni/NiO/Pt multilayers were fabricated vi...
Article
Full-text available
THz radiation emitted by ferromagnetic/non-magnetic bilayers is a new emergent field in ultra-fast spin physics phenomena with a lot of potential for technological applications in the terahertz (THz) region of the electromagnetic spectrum. The role of antiferromagnetic layers in the THz emission process is being heavily investigated at the moment....
Poster
Full-text available
Recently, quite some of research effort has been put on the investigation of perpendicular magnetic anisotropy (PMA) and exchange bias (EB) at transition metal/oxide interfaces and the relevant applications in magnetic storage and ultrafast spintronics. In this work we provide a brief review of the magnetic properties of a few multilayered systems...
Preprint
Full-text available
We show in theory and experiment that in periodically patterned spintronic THz emitters (STE), charge dynamics can modify the emission spectrum in a well-controlled way. Characterization of sub-wavelength patterned STE at frequencies up to 30 THz shows that the STE's emission spectrum systematically changes with emitter size. The spectral intensity...
Article
Thin layers of ferromagnetic/non-magnetic bimetallic heterostructures have become the focal point of spintronics, primarily due to their capacity to convert spin to charge current, leveraging the spin- and inverse spin Hall effects. However, the interfacial properties and morphologies can significantly influence this conversion. Hence, we employed...
Preprint
We present a study of the damping and spin pumping properties of CoFeB/X/Pt systems with $\rm X=Al,Cr$ and $Ta$. We show that the total damping of the CoFeB/Pt systems is strongly reduced when an interlayer is introduced independently of the material. Using a model that considers spin relaxation, we identify the origin of this contribution in the m...
Article
We show that to correctly describe the ultrafast currents in spintronic terahertz emitters it is necessary to take charge equilibration into account. It has been extensively described that in a spintronic terahertz emitter a femtosecond laser pulse can induce a perpendicular spin current that is then converted by the inverse spin Hall effect into a...
Article
Full-text available
Co/CoO multilayers are fabricated by means of radio-frequency magnetron sputtering. For the formation of each multilayer period, a Co layer is initially produced followed by natural oxidation. Platinum is used not only as buffer and capping layers, but also in the form of intermediate ultrathin layers to enhance perpendicular magnetic anisotropy. T...
Article
We present a study of the damping and spin pumping properties of CoFeB/X/Pt systems with X = Al,Cr and Ta. We show that the total damping of the CoFeB/Pt systems is strongly reduced when an interlayer is introduced independently of the material. Using a model that considers spin relaxation, we identify the origin of this contribution in the magneti...
Preprint
Full-text available
We show that to correctly describe the ultrafast currents in spintronic THz emitters it is necessary to take charge equilibration into account. The charge current which is locally induced by a fs laser pulse and the inverse spin-Hall effect (ISHE) leads to ultrafast charging phenomena at the edge of the illuminated area. Subsequent discharging lead...
Article
Full-text available
Terahertz emission from ferromagnetic/non-magnetic spintronic heterostructures had been demonstrated as pump wavelength-independent. We report, however, the pump wavelength dependence of terahertz emission from an optimized Fe/Pt spintronic bilayer on MgO substrate. Maximum terahertz generation per total pump power was observed in the 1200- to 1800...
Article
Full-text available
Ni0.95Fe0.05/NiFeO multilayers were fabricated by radio frequency magnetron sputtering and natural oxidation. Doping of Ni by only 5 at. % Fe results in enhanced layering quality as X-ray reflectivity reveals. Due to magnetostatic anisotropy, the multilayers were found to be in-plane magnetized. The influence of mild thermal annealing (T = 525 K) o...
Preprint
Full-text available
Recent developments in nanomagnetism and spintronics have enabled the use of ultrafast spin physics for terahertz (THz) emission. Spintronic THz emitters, consisting of ferromagnetic FM / non-magnetic (NM) thin film heterostructures, have demonstrated impressive properties for the use in THz spectroscopy and have great potential in scientific and i...
Article
Full-text available
Recent developments in nanomagnetism and spintronics have enabled the use of ultrafast spin physics for terahertz (THz) emission. Spintronic THz emitters, consisting of ferromagnetic FM / non-magnetic (NM) thin film heterostructures, have demonstrated impressive properties for the use in THz spectroscopy and have great potential in scientific and i...
Article
Full-text available
We study the steering of visible light using a combination of magneto-optical effects and the reconfigurability of magnetic domains in yttrium-iron garnet films. The spontaneously formed stripe domains are used as a field-controlled optical grating, allowing for active spatiotemporal control of light. We discuss the basic ideas behind the approach...
Preprint
Full-text available
We study the steering of visible light using a combination of magneto-optical effects and the reconfigurability of magnetic domains in Yttrium-Iron Garnet films. The spontaneously formed stripe domains are used as a field-controlled optical grating, allowing for active spatiotemporal control of light. We discuss the basic ideas behind the approach...
Article
Full-text available
We report the generation and detection of spin–orbit torque ferromagnetic resonance (STFMR) in micropatterned epitaxial Fe/Pt bilayers grown by molecular beam epitaxy. The magnetic field dependent measurements at an in-plane magnetic field angle of 45° with respect to the microwave-current direction reveal the presence of two distinct voltage peaks...
Poster
Full-text available
In the last decades, research and investment efforts have been made to study the magnetic properties of thin films because of their obvious practical applications, such as perpendicular magnetic anisotropy (PMA). A very promising way to handle the properties of the magnetic thin films is to fabricate heterostructures of them, i.e., combination of m...
Preprint
We report the generation and detection of spin-orbit torque ferromagnetic resonance (STFMR) in micropatterned epitaxial Fe/Pt bilayers grown by molecular beam epitaxy. The magnetic field dependent measurements at an in-plane magnetic field angle of 45 degrees with respect to the microwave-current direction reveal the presence of two distinct voltag...
Article
Full-text available
We have explored the impact of elevated growth and annealing temperatures on the local interfacial structure of thin Fe(12 nm)/Pt(10 nm) spintronic bilayers, epitaxially grown on MgO (100), and their correlation to magnetization reversal and dynamics. Electron-beam evaporation growth and subsequent annealing at 450 °C causes significant roughening...
Article
Full-text available
Ultrathin films of Ni0.9Co0.1 were grown by radio frequency magnetron sputtering. By means of a periodic natural oxidation procedure they were transformed into Ni0.9Co0.1/NiCoO multilayers. Room temperature hysteresis loops recorded via the magneto-optic Kerr effect have revealed over all in-plane magnetic anisotropy due to magnetostatic anisotropy...
Article
Full-text available
The field of THz spintronics is a novel direction in the research field of nanomagnetism and spintronics that combines magnetism with optical physics and ultrafast photonics. The experimental scheme of the field involves the use of femtosecond laser pulses to trigger ultrafast spin and charge dynamics in thin films composed of ferromagnetic and non...
Article
The influence of mild thermal annealing and nickel addition on the magnetic properties of Co-CoO multilayers is investigated. Co-CoO and CoNi-CoNiO multilayers were fabricated by radio frequency magnetron sputtering and natural oxidation. Their magnetic properties have been studied via the magneto-optical Kerr effect and a vector network analyzer f...
Preprint
We investigate the THz emission characteristics of ferromagnetic/non-magnetic metallic heterostructures, focusing on thin Fe/Pt bilayers. In particular, we report on the impact of optimized crystal growth of the epitaxial Fe layers on the THz emission amplitude and spectral bandwidth. We demonstrate an enhancement of the emitted intensity along wit...
Preprint
Full-text available
The field of THz spintronics is a novel direction in the research field of spintronics that combines magnetism with optical physics and ultrafast photonics. The experimental scheme of the field involves the use of femtosecond laser pulses to trigger ultrafast spin and charge dynamics in bilayers composed of ferromagnetic (FM) and non-magnetic (NM)...
Conference Paper
The field of THz spintronics is a novel direction in the research field of spintronics that combines magnetism with optical physics and ultrafast photonics. The experimental scheme of the field involves the use of femtosecond laser pulses to trigger ultrafast spin and charge dynamics in bilayers composed of ferromagnetic (FM) and non- magnetic (NM)...
Article
Full-text available
The fundamental phenomenon of Bose–Einstein condensation has been observed in different systems of real particles and quasiparticles. The condensation of real particles is achieved through a major reduction in temperature, while for quasiparticles, a mechanism of external injection of bosons by irradiation is required. Here, we present a new and un...
Preprint
Full-text available
Thin Yttrium Iron Garnet (YIG) is a promising material for integrated magnonics. In order to introduce YIG into nanofabrication processes it is necessary to fabricate very thin YIG films with a thickness well below 100 nm while retaining the extraordinary magnetic properties of the material, especially its long magnon lifetime and spin wave propaga...
Article
Full-text available
We unravel the underlying near-field mechanism of the enhancement of the magneto-optical activity of bismuth-substituted yttrium iron garnet films (Bi:YIG) loaded with gold nanoparticles. The experimental results show that the embedded gold nanoparticles lead to a broadband enhancement of the magneto-optical activity with respect to the activity of...
Article
Full-text available
We investigate spin pumping and the effective spin mixing conductance in heterostructures based on magnetic oxide trilayers composed of La0.7Sr0.3MnO3 (LSMO), LaNiO3 (LNO), and SrRuO3 (SRO). The heterostructures serve as a model system for an estimation of the effective spin mixing conductance at the different interfaces. Our results show that by i...
Article
Full-text available
Thin film Yttrium Iron Garnet (YIG) is a promising material for integrated magnonics. In order to introduce YIG into nanofabrication processes it is necessary to fabricate very thin YIG films with a thickness well below 100 nm while retaining the extraordinary magnetic properties of the material, especially its long magnon lifetime and spin wave pr...
Article
Full-text available
***This is a peer-reviewed paper published in the JOURNAL OF THE JAPAN SOCIETY OF INFRARED SCIENCE AND TECHNOLOGY, Vol. 29, Issue No. 2, pp. 57-62 (February 2020).*** A spintronic bilayer structure, which consists of 2-nm Fe and 3-nm Pt epitaxial grown on 500-µm MgO substrate, was investigated as a terahertz (THz) source for different optical pump...
Conference Paper
Full-text available
Illuminating metallic spintronic heterostructures with ultrafast laser pulses can generate terahertz (THz) radiation due to spin current-to-charge current conversion. Such metallic spintronic heterostructures are essentially ultrathin ferromagnetic and non-ferromagnetic metallic layers stacked on appropriate substrates. They are particularly attrac...
Article
Interface induced phenomena in layered magnetic/non-magnetic structures have led to big discoveries, such as giant magnetoresistance, which has defined the field of spintronics. Interfaces are capable of inducing magnetism even in non-magnetic layers, like platinum. Here, we investigated the static magnetic properties of modified interfaces in Fe/P...
Preprint
Full-text available
We investigate spin pumping and the effective spin mixing conductance in heterostructures based on magnetic oxide trilayers composed of La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO), LaNiO$_3$ (LNO), and SrRuO$_3$ (SRO). The heterostructures serve as a model system for an estimation of the effective spin mixing conductance at the different interfaces. Our res...
Article
Full-text available
Spintronic ferromagnetic/non-magnetic heterostructures are novel sources for the generation of THz radiation based on spin-to-charge conversion in the layers. The key technological and scientific challenge of THz spintronic emitters is to increase their intensity and frequency bandwidth. Our work reveals the factors to engineer spintronic Terahertz...
Conference Paper
Metallic spintronic heterostructures consisting of ultrathin ferromagnetic (FM) and non-ferromagnetic (NM) layers emit THz radiation through a distinct and efficient THz generation mechanism, which arises from the conversion of spin current generated in the FM layers into transverse charge current in the NM layers [1, 2]. We have previously demonst...
Preprint
Full-text available
We unravel the underlying near-field mechanism of the enhancement of the magneto-optical activity of bismuth-substituted yttrium iron garnet films (Bi:YIG) loaded with gold nanoparticles. The experimental results show that the embedded gold nanoparticles lead to a broadband enhancement of the magneto-optical activity with respect to the activity of...
Poster
Full-text available
Spintronic heterostructures are emerging and promising THz sources due to their considerable advantages over other conventional THz emitters. In a recent study [6], an Fe/Pt spintronic bilayer structure was observed to be an efficient THz source when using either 800-nm or 1550-nm pump wavelength. In this paper, we performed terahertz (THz)-time do...
Poster
Full-text available
Spintronic heterostructures consisting of layers of ferromagnetic (FM) and nonmagnetic (NM) metals, are promising THz sources. In a previous study [5], an Fe/Pt spintronic bilayer structure was observed to be an effective THz radiation source when using either 800-nm or 1.55-μm excitation wavelengths. In this paper, excitation wavelengths of 400-nm...
Article
Full-text available
Large surface plasmon polariton assisted enhancement of the magneto-optical activity has been observed in the past, through spectral measurements of the polar Kerr rotation in Co hexagonal antidot arrays. Here, we report a strong thickness dependence, which is unexpected given that the Kerr effect is considered a surface sensitive phenomena. The ma...
Preprint
Spintronic ferromagnetic/non-magnetic heterostructures are novel sources for the generation of THz radiation based on the spin-to-charge conversion in the films. The key technological and scientific challenge of THz spintronic emitters is to increase their low intensity and frequency bandwidth. Our work reveals the factors to engineer both by intro...
Article
We present angle-dependent measurements of the damping properties of epitaxial Fe layers with MgO, Al, and Pt capping layers. Based on the preferential distribution of lattice defects following the crystal symmetry, we make use of a model of the defect density to separate the contribution of two-magnon scattering to the damping from the isotropic c...
Preprint
We present angle dependent measurements of the damping properties of epitaxial Fe layers with MgO, Al and Pt capping layers. Based on the preferential distribution of lattice defects following the crystal symmetry, we make use of a model of the defect density to separate the contribution of two-magnon scattering to the damping from the isotropic co...
Preprint
Full-text available
We present angle dependent measurements of the damping properties of epitaxial Fe layers with MgO, Al and Pt capping layers. Based on the preferential distribution of lattice defects following the crystal symmetry, we make use of a model of the defect density to separate the contribution of two-magnon scattering to the damping from the isotropic co...
Poster
Full-text available
In this work, we will demonstrate that an optimized spintronic bilayer of iron and platinum thin films is a versatile and convenient source of terahertz (THz) radiation. We will discuss the mechanism for spintronic THz emission and report efficient THz generation using 1550-nm (communication wavelength) optical pump pulses from a femtosecond fiber...
Article
Full-text available
We report on the determination of the spin Hall angle and the identification of the role of the interface roughness for the inverse spin Hall effect (ISHE) in ultra-clean, defect-reduced epitaxial Pt films. By applying vector network analyzer ferromagnetic resonance spectroscopy to a series of single crystalline Fe (12 nm) /Pt (t$_\text{Pt}$) bilay...
Article
Full-text available
Recent studies in spintronics have highlighted ultrathin magnetic metallic multilayers as a novel and very promising class of broadband terahertz radiation sources. Such spintronic multilayers consist of ferromagnetic (FM) and non-magnetic (NM) thin films. When triggered by ultrafast laser pulses, they generate pulsed THz radiation due to the inver...
Conference Paper
Spintronic heterostructures consisting of ferromagnetic and non-magnetic metal thin films have been demonstrated as novel and highly promising sources of broadband THz radiation. Such spintronic THz emitters had only been intensively investigated so far at 800-nm excitation wavelength using femtosecond Ti:sapphire lasers. In this work, we demonstra...
Article
Full-text available
We report on efficient generation of pulsed broadband terahertz radiation utilizing the inverse spin hall effect in Fe/Pt bilayers on MgO and sapphire substrates. The emitter was optimized with respect to layer thickness, growth parameters, substrates and geometrical arrangement. The experimentally determined optimum layer thicknesses were in quali...
Article
Full-text available
The optical and magneto-optical behavior in periodically nanostructured surfaces at the threshold of surface continuity is revealed. We address Co films that evolve from an island-like array to a connecting network of islands that form a membrane pattern. The analysis of magneto-optical spectra as well as numerical simulations show significant diff...
Article
Full-text available
We propose a microscopic mechanism to explain and unify the many recent observations of spin pumping in metallic spintronic systems. The mechanism invokes parallels with the physics of Dynamic Nuclear Polarisation and it predicts that microwave spin pumping is equally viable - albeit with different efficiencies - in magnetic and non-magnetic metals...
Article
Full-text available
We investigate spin pumping phenomena in polycrystalline CoFeB/Pt and CoFeB/Ta bilayers and the correlation between the effective spin-mixing conductance g ↑↓ eff and the obtained voltages generated by the spin-to-charge current conversion via the inverse spin Hall effect in the Pt and Ta layers. For this purpose, we measure the in-plane angular de...
Article
Full-text available
The spin-pumping mechanism is probed through a tunnelling MgO interlayer in Fe/Pt bilayers. We show by ferromagnetic resonance technique and spin-pumping experiments that spin currents can tunnel through the MgO interlayer for thickness up to 2~{nm} and can produce significant voltages in the Pt layer. The electrical detection of spin-pumping furth...
Article
We quantify the relative weight of inverse spin Hall and spin rectification effects occurring in RF-sputtered polycrystalline permalloy, molecular beam epitaxy-grown epitaxial iron and liquid phase epitaxy-grown yttrium-iron-garnet bilayer systems with different capping materials. To distinguish the spin rectification signal from the inverse spin H...
Article
Full-text available
We investigate spin pumping phenomena in polycrystalline CoFeB/Pt and CoFeB/Ta bilayers and the correlation between the effective spin mixing conductance $g^{\uparrow\downarrow}_{\rm eff}$ and the obtained voltages generated by the spin-to-charge current conversion via the inverse spin Hall effect in the Pt and Ta layers. For this purpose we measur...
Article
Full-text available
We reveal the influence of the thickness of the ferromagnetic layer on the surface plasmon polariton assisted enhancement of the polar magneto-optic Kerr effect. The optical and magneto-optical response is strongly altered by the thickness of the magnetic layer as shown in specular reflectivity and polar magneto-optical Kerr effect measurements. Th...