Plamen Stamenov

Plamen Stamenov
Trinity College Dublin | TCD · School of Physics

About

52
Publications
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Publications

Publications (52)
Article
Pendant droplets of water and paramagnetic solutions are studied in the presence of uniform and nonuniform magnetic fields produced by small permanent magnet arrays, both in static conditions and during dynamic pinch-off. Static measurements of the droplet shape are analysed in terms of an apparent surface tension γ app or an effective density ρ ef...
Article
In the present study, the liquidus temperature, mixing enthalpy, and atomic mismatch factor are used to predict and empirically evaluate the amorphisation capability of Co-Fe-B alloys fabricated by melt spinning. Based on this approach, five out of seven alloys have an amorphous structure, confirming the capability of the proposed model in predicti...
Article
Repeated uniform switching of the magnetization of thin films of ferrimagnetic amorphous Gd x (FeCo) 1−x in response to single fast laser pulses is well established. Here, we report unusual toggle switching in thin films of sperimagnetic amorphous Dy x Co 1−x and Tb x Co 1−x with x ≈ 0.25 irradiated with single 200 fs pulses of 800 nm laser light....
Article
Perpendicular heterostructures based on a ferrimagnetic Mn2RuxGa (MRG) layer and a ferromagnetic Co/Pt multilayer were examined to understand the effects of different spacer layers (V, Mo, Hf, HfOx and TiN) on the interfaces with the magnetic electrodes, after annealing at 350∘C. Loss of perpendicular anisotropy in MRG is strongly correlated with a...
Preprint
Full-text available
Repeated uniform switching of the magnetization of thin films of ferrimagnetic amorphous Gd$_{x}$(FeCo)$_{1-x}$ in response to single fast laser pulses is well established. Here we report unusual toggle switching in thin films of sperimagnetic amorphous Dy$_x$Co$_{1-x}$ and Tb$_x$Co$_{1-x}$ with $\it{x} \simeq$ 0.25 irradiated with single 200 fs pu...
Article
Three natural specimens of hematite are characterized using X-ray diffraction, magnetometry, IR/Raman and Mössbauer spectroscopy, with focus on the Morin transition. All are exfoliated by grinding and prolonged sonication in dimethylformamide, followed by centrifuging to extract exfoliated debris from the supernatant. This material is characterized...
Article
A thermodynamics-based approach, Calculation of Phase Diagram (CALPHAD), combined with topological instability parameters are proposed and experimentally evaluated, in order to optimise in-situ nanocrystallisation of rapidly quenched CoFeB alloys and exploit their remarkable Bs = 1.57 T. The high Ms of the alloy is attributed to the precipitation o...
Preprint
We investigate the evolution of spin polarization, spontaneous Hall angle (SHA), saturation magnetization and Curie temperature of $B2$-ordered Fe$_{60}$Al$_{40}$ thin films under varying antisite disorder, induced by Ne$^{+}$-ion irradiation. The spin polarization increases monotonically as a function of ion fluence. A relatively high polarization...
Preprint
Full-text available
Perpendicular heterostructures based on a ferrimagnetic Mn2RuxGa (MRG) layer and a ferromagnetic CoPt multilayer were examined to understand the effects of different spacer layers (V, Mo, Hf, HfOx and TiN) on the interfaces with the magnetic electrodes, especially after annealing at 350 C. Loss of perpendicular anisotropy in MRG is strongly correla...
Article
We report on first-principles calculations of spin-transfer torque (STT) in epitaxial magnetic tunnel junctions (MTJs) based on ferrimagnetic tetragonal Mn3Ga electrodes, both as analyzer in a Fe/MgO stack, and also in an analogous stack with a second Mn3Ga electrode (instead of Fe) as polarizer. Solving the ballistic transport problem (NEGF+DFT) f...
Article
Full-text available
We study the demagnetization dynamics of the fully compensated half-metallic ferrimagnet Mn2RuxGa. While the two antiferromagnetically coupled sublattices are both composed of manganese, they exhibit different temperature dependencies due to their differing local environments. The sublattice magnetization dynamics triggered by femtosecond laser pul...
Conference Paper
Dynamic tuning of the luminescence enhancement of fluorescent emitters in the near infrared spectral range is achieved through the coupling of the quantum emitters to noble metal nanostructures on thin film vanadium dioxide (VO 2 ).
Preprint
Full-text available
Compensated ferrimagnets are promising materials for fast spintronic applications based on domain wall motion as they combine the favourable properties of ferromagnets and antiferromagnets. They inherit from antiferromagnets immunity to external fields, fast spin dynamics and rapid domain wall motion. From ferromagnets they inherit straightforward...
Article
Full-text available
The development of high‐density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat‐assisted magnetic recording was developed,...
Article
We present the nanofabrication and transport properties of single silicon nanowires (NWs) having mean widths in the range from sub-30 to 500 nm. Hall effect measurements are undertaken in the magnetic fields of 14 T at 300 K. The NWs are defined by electron-beam lithography (EBL) using the negative tone resist hydrogen silsesquioxane (HSQ) as a mas...
Article
Full-text available
Soft magnetic amorphous materials with ultra-low power loss are highly desirable for high-frequency drive applications. The present work demonstrates the high-frequency power loss performance and underlying loss mechanisms in ultra-thin amorphous alloys. This is achieved by rapid-quenching amorphous alloys of Co-, CoFe- and Fe-rich systems, investi...
Preprint
Full-text available
We report on first principles calculations of spin-transfer torque (STT) in epitaxial magnetic tunnel junctions (MTJs) based on ferrimagnetic tetragonal Mn$_3$Ga electrodes, both as analyser in a Fe/MgO stack, and also in an analogous stack with Mn$_3$Ga electrode (instead of Fe) as polariser. Solving the ballistic transport problem (NEFG+DFT) for...
Preprint
Full-text available
The development of high-density magnetic recording media is limited by the superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat assisted magnetic recording (HAMR) has...
Article
As-cast ingots of Mn100−xZx with Z = Al, Ge, Mn, Fe and Co all have the A13 βMn structure up to some maximum value of x. The magnetic susceptibility of pure βMn is ≈ 9 × 10⁻⁴ from 4 to 400 K, but the field-cooled and zero-field-cooled susceptibilities of all doped samples increase at low temperature and they bifurcate at a spin-freezing temperature...
Article
The mechanisms that limit the power loss performance in melt-spun amorphous ribbons have been investigated through DC and AC magnetic characterization methods. The measured total power loss is resolved into hysteresis, eddy current, and anomalous losses. The anomalous loss is found to account for more than 90% of the total loss, which significantly...
Article
Full-text available
Sm(CoFeCuZr)z permanent magnets are of great technological interest due to their good magnetic performance and excellent thermal stability. The Fe content plays a key role for magnetic properties, determining the maximum energy product and the highest working temperature. Here we investigated the Fe site preferences in Sm(CoFeCuZr)z magnets with Fe...
Article
A flux source with four rotatable permanent magnet rods having access from two perpendicular directions through gaps exceeding the rod diameter can produce a continuously-variable flux density of up to ±300 mT at the centre when high-grade Nd-Fe-B magnets are used. The trade-off between field, access and torque in this mangle design is discussed. T...
Article
Phase transformation driven soft magnetic properties have been correlated through different stages of nano-crystallization of Co-based amorphous alloys, via transverse magnetic annealing, by combining structural, magnetothermal, domain imaging, and AC/DC magnetometry techniques. The nano-crystallization starts by nucleation and growth process of so...
Article
Full-text available
There is an increasing demand for permanent magnets with high‐temperature stability. Normally, the magnets are heat treated above the operating temperature range to saturate the irreversible losses, thereby producing magnets that are stable, but with significantly degraded performance. In addition, uncertainty about the losses in differently shaped...
Article
Full-text available
Due to its negligible spontaneous magnetization, high spin polarization and giant perpendicular magnetic anisotropy, Mn2RuxGa (MRG) is an ideal candidate as an oscillating layer in THz spin-transfer-torque nano-oscillators. Here, the effect of ultrathin Al and Ta diffusion barriers between MRG and MgO in perpendicular magnetic tunnel junctions is i...
Preprint
Full-text available
Antiferromagnets and compensated ferrimagnets offer opportunities to investigate spin dynamics in the 'terahertz gap' because their resonance modes lie in the 0.3 THz to 3 THz range. Despite some inherent advantages when compared to ferromagnets, these materials have not been extensively studied due to difficulties in exciting and detecting the hig...
Article
Ultra-thin soft magnetic amorphous ribbons of Co-Fe-B-Si-Nb alloy were synthesised by a single step rapid-quenching approach to acquire advantage of improved material performance and lower costs over commercial amorphous alloys. The amorphous ribbons of approximately 5.5 µm thicknesses were quenched by a single roller melt spinner in a single-step...
Article
Radio frequency identification (RFID) is a technology permeating both everyday life and scientific applications alike. The most prolific passive tag-based system uses inductively-powered tags with no internal power source [V. Chawla and D. S. Ha, “An overview of passive RFID,” IEEE Commun. Mag. 45(9), 11–17 (2007)]. Here we demonstrate an inductive...
Article
We show how a charge current through a single antiferromagnetic layer can excite and control self-oscillations. Sustained oscillations with tunable amplitudes and frequencies are possible in a variety of geometries using certain classes of noncentrosymmetric materials that exhibit finite dissipative spin-orbit torque. We compute the steady-state ph...
Article
Full-text available
Magnetotransport is investigated in thin films of the half-metallic ferrimagnet Mn2RuxGa in pulsed magnetic fields of up to 58 T. A nonvanishing Hall signal is observed over a broad temperature range, spanning the compensation temperature (155 K), where the net magnetic moment is strictly zero, the anomalous Hall conductivity is 6673Ω−1m−1, and the...
Preprint
Magnetotransport is investigated in thin films of the half-metallic ferrimagnet Mn$_2$Ru$_x$Ga in pulsed magnetic fields of up to 58 T. A non-vanishing Hall signal is observed over a broad temperature range, spanning the compensation temperature 155 K, where the net magnetic moment is strictly zero, the anomalous Hall conductivity is 6673 $\Omega^{...
Preprint
Spin-orbit torques can control antiferromagnetic dynamics. We determine the form of the reactive and dissipative spin-orbit torques (SOT) in the non-centrosymmetric material CuMnAs, and show how a charge current in a single antiferromagnetic layer can excite and control self-oscillations. We predict that sustained oscillations with tunable amplitud...
Article
Full-text available
With the continuous shrinkage of the footprint of inductors and transformers in modern power supplies, higher flux, while still low-loss metallic replacements of traditional ferrite materials are becoming an intriguing alternative. One candidate replacement strategy is based on amorphous CoFeBSi soft-magnetic alloys, in their metallic glass form. H...
Article
Full-text available
Ionic liquid gating is a versatile method for inducing a metal-insulator transition in field-effect transistor device structures. The mechanism of carrier doping in metal oxide films is under debate. Ionic liquid gating of a WO3 film-based field effect transistor is discussed in this report. Flat and relatively smooth WO3 films were deposited on Sr...
Article
Ferrimagnetic Mn2FexGa(0.26≤x≤1.12) thin films have been characterized by x-ray diffraction, magnetometry, x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and Mössbauer spectroscopy with the aim of determining the structure and site-specific magnetism of this tetragonal, D022-structure Heusler compound. High-quality epitaxial film...
Article
Full-text available
Ferrimagnetic Mn$_2$Fe$_x$Ga $(0.26 \leq x \leq 1.12)$ thin films have been characterised by X-ray diffraction, SQUID magnetometry, X-ray absorption spectroscopy, X-ray magnetic circular dichroism and M\"{o}ssbauer spectroscopy with the aim of determining the structure and site-specific magnetism of this tetragonal, D0$_{22}$-structure Heusler comp...
Article
Switching of magnetization via spin-orbit torque provides an efficient alternative for nonvolatile memory and logic devices. However, to achieve deterministic switching of perpendicular magnetization, an external magnetic field collinear with the current is usually required, which makes these devices inappropriate for practical applications. In thi...
Article
Both polycrystalline and single-crystal films of iron-substituted strontium titanate, Sr(Ti0.65Fe0.35)O3−δ, prepared by pulsed laser deposition, show room-temperature magnetism and Faraday rotation, with the polycrystalline films exhibiting higher saturation magnetization and Faraday rotation. The magnetic properties vary with the oxygen pressure a...
Article
The polar corundum structure type offers a route to new room temperature multiferroic materials, as the partial LiNbO3-type cation ordering that breaks inversion symmetry may be combined with long range magnetic ordering of high spin d5 cations above room temperature in the AFeO3 system. We report the synthesis of a polar corundum GaFeO3 by a high-...
Article
An increase in microwave permeability is a prerequisite for reducing the thickness of radar absorber coatings. The aim of this paper is to increase the magnetic loss of commercial carbonyl iron particles for fabricating wideband microwave absorbers with a multilayer structure. For this purpose, carbonyl iron particles were milled and their static a...
Article
Manipulation of the magnetization of a perpendicular ferromagnetic free layer by spin-orbit torque (SOT) is an attractive alternative to spin-transfer torque (STT) in oscillators and switches such as magnetic random-access memory (MRAM) where a high current is passed across an ultrathin tunnel barrier. A small symmetry-breaking bias field is usuall...
Article
Full-text available
The Heusler compound Mn2RuxGa (MRG) may well be the first compensated half metal. Here, the structural, magnetic and transport properties of thin films of MRG are discussed. There is evidence of half-metallicity up to x = 0.7, and compensation of the two Mn sublattice moments is observed at specific compositions and temperatures, leading to a zero-...
Article
Enhanced magnetostriction in iron-rich Fe–Ga alloys has been attributed to a heterogeneous nanostructure with tetragonal inclusions, although direct experimental evidence for their structure was lacking. Here we use transmission electron microscopy to show that melt-spun, (001) textured Fe83Ga17 ribbons contain 3 nm inclusions with c-axis Ga–Ga pai...
Article
Full-text available
Magnetization reversal of a perpendicular ferromagnetic free layer by spin-orbit torque (SOT) is an attractive alternative to spin-transfer torque (STT) switching in magnetic random-access memory (MRAM) where the write process involves passing a high current across an ultrathin tunnel barrier. A small symmetry-breaking bias field is usually needed...
Article
Full-text available
Ferrimagnetic Mn3Ga exhibits a unique combination of low saturation magnetization (Ms = 0.11 MA m-1) and high perpendicular anisotropy with a uniaxial anisotropy constant of Ku = 0.89 MJ m-3. Epitaxial c-axis films exhibit spin polarization as high as 58%, measured using point contact Andreev reflection. These epitaxial films will be able to suppor...
Article
Ferromagnetic magnetization curve of certain oxide thin films, whether undoped or doped 3d ions, shows a characteristic anhysteretic approach to saturation of the form M Mstanh(H/H0), which is independent of temperature below RT. There is no magnetic ordering of the dopant ions, but ferromagnetism is associated with Stoner splitting of a defect-rel...

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