arXiv subjects

Peter Svedlindh

Publications and source records attributed to Peter Svedlindh.

At least 37 records · Page 2Linked to original sources

arXiv2021

Data-driven design of a new class of rare-earth free permanent magnets

A new class of rare-earth-free permanent magnets is proposed. The parent compound of this class is Co$_3$Mn$_2$Ge, and its discovery is the result of first principles theory combined with experimental synthesis and characterisation. The theory is based on a high-throughput/data-mining search among materials listed in the ICSD database. From ab-initio theory of the defect free material it is predicted that the saturation magnetization is 1.71 T, the uniaxial magnetocrystalline anisotropy is 1.44 MJ/m$^3$, and the Curie temperature is 700 K. Co$_3$Mn$_2$Ge samples were then synthesized and characterised with respect to structure and magnetism. The crystal structure was found to be the MgZn$_2$-type, with partial disorder of Co and Ge on the crystallographic lattice sites. From magnetization measurements a saturation polarization of 0.86 T at 10 K was detected, together with a uniaxial magnetocrystalline anisotropy constant of 1.18 MJ/m$^3$, and the Curie temperature of $T_{\rm C}$ = 359 K. These magnetic properties make Co$_3$Mn$_2$Ge a very promising material as a rare-earth free permanent magnet, and since we can demonstrate that magnetism depends critically on the amount of disorder of the Co and Ge atoms, a further improvement of the magnetism is possible. From the theoretical works, a substitution of Ge by neighboring elements suggest two other promising materials - Co$_3$Mn$_2$Al and Co$_3$Mn$_2$Ga. We demonstrate here that the class of compounds based on $T_3$Mn$_2$X (T = Co or alloys between Fe and Ni; X=Ge, Al or Ga) in the MgZn$_2$ structure type, form a new class of rare-earth free permanent magnets with very promising performance.

cond-mat.mtrl-sci↗

arXiv2020

Field induced crossover in critical behaviour and direct measurement of the magnetocaloric properties of La0.4Pr0.3Ca0.1Sr0.2MnO3

La0.4Pr0.3Ca0.1Sr0.2MnO3 has been investigated as a potential candidate for room temperature magnetic refrigeration. Results from X-ray powder diffraction reveal an orthorhombic structure with Pnma space group. The electronic and chemical properties have been confirmed by X-ray photoelectron spectroscopy and ion-beam analysis. A second-order paramagnetic to ferromagnetic transition was observed near room temperature (289 K), with a mean-field like critical behaviour at low field and a tricritical mean-field like behaviour at high field. The field induced crossover in critical behaviour is a consequence of the system being close to a first-order magnetic transition in combination with a magnetic field induced suppression of local lattice distortions. The lattice distortions consist of interconnected and weakly distorted pairs of Mn-ions, where each pair shares an electron and a hole, dispersed by large Jahn-Teller distortions at Mn3+ lattice sites. A comparatively high value of the isothermal entropy-change (3.08 J/kg-K at 2 T) is observed and the direct measurements of the adiabatic temperature change reveal a temperature change of 1.5 K for a magnetic field change of 1.9 T.

cond-mat.mtrl-sci↗

arXiv2020

Intertwined Magnetic Sub-Lattices in the Double Perovskite Compound LaSrNiReO6

We report a muon spin rotation ($μ^{+}$SR) study of the magnetic properties of the double perovskite compound LaSrNiReO$_{6}$. Using the unique length and time scales of the $μ^{+}$SR technique, we successfully clarify the magnetic ground state of LaSrNiReO$_{6}$, which was previously deemed as a spin glass state. Instead, our $μ^{+}$SR results point towards a long-range dynamically ordered ground state below $T_{\rm C}= 23$ K, for which a static limit is foreseen at $T=0$. Furthermore, between 23 K$ 250$ K) state. Our results reveal how two separate, yet intertwined magnetic lattices interact within the unique double perovskite structure and the importance of using complementary experimental techniques to obtain a complete understanding of the microscopic magnetic properties of complex materials.

cond-mat.str-el↗

arXiv2020

Evolution of Griffiths Phase and Critical Behaviour of La1-xPbxMnO3+-y Solid Solutions

Polycrystalline La1-xPbxMnO3+-y (x = 0.3, 0.35, 0.4) solid solutions were prepared by solid state reaction method and their magnetic properties have been investigated. Rietveld refinement of X-ray powder diffraction patterns showed that all samples are single phase and crystallized with the rhombohedral structure in the R-3c space group. A second order paramagnetic to ferromagnetic phase transition was observed for all materials. The Griffiths phase (GP), identified from the temperature dependence of the inverse susceptibility, was suppressed by increasing magnetic field and showed a significant dependence on A-site chemical substitution. The critical behaviour of the compounds was investigated near to their Curie temperatures, using intrinsic magnetic field data. The critical exponents (\b{eta}, γ and δ) are close to the mean-field approximation values for all three compounds. The observed mean-field like behaviour is a consequence of the GP and the formation of ferromagnetic clusters. Long-range ferromagnetic order is established as the result of long-range interactions between ferromagnetic clusters. The magnetocaloric effect was studied in terms of the isothermal entropy change. Our study shows that the material with the lowest chemical substitution (x = 0.3) has the highest potential (among the three compounds) as magnetic refrigerant, owing to its higher relative cooling power (258 J/kg at 5 T field) and a magnetic phase transition near room temperature.

cond-mat.mtrl-sci↗

arXiv2020

Damping-like Torque in Monolayer 1T-TaS$_2$

A damping-like spin orbit torque (SOT) is a prerequisite for ultralow power spin logic devices. Here, we report on the damping-like SOT in just one monolayer of the conducting transition metal dichalcogenide (TMD) TaS$_2$ interfaced with a NiFe (Py) ferromagnetic layer. The charge-spin conversion efficiency is found to be 0.25$\pm$0.03 and the spin Hall conductivity (2.63 $\times$ 10$^5$ $\frac{\hbar}{2e}$ $Ω^{-1}$ m$^{-1}$) is found to be superior to values reported for other TMDs. The origin of this large damping-like SOT can be found in the interfacial properties of the TaS$_2$/Py heterostructure, and the experimental findings are complemented by the results from density functional theory calculations. The dominance of damping-like torque demonstrated in our study provides a promising path for designing next generation conducting TMD based low-powered quantum memory devices.

cond-mat.mes-hall↗

arXiv2019

Impact of the crystal orientation on spin-orbit torques in Fe/Pd bilayers

Spin-orbit torques in ferromagnetic (FM)/non-magnetic (NM) heterostructures offer more energy-efficient means to realize spin-logic devices; however, their strengths are determined by the heterostructure interface. This work examines crystal orientation impact on the spin-orbit torque efficiency in different Fe/Pd bilayer systems. Spin torque ferromagnetic measurements evidence that the damping-like torque efficiency is higher in epitaxial than in polycrystalline bilayer structures while the field-like torque is negligible in all bilayer structures. The strength of the damping-like torque decreases with deterioration of the bilayer epitaxial quality. The present finding provides fresh insight for the enhancement of spin-orbit torques in magnetic heterostructures.

cond-mat.mtrl-sci↗

arXiv2019

Magnetic proximity in a van der Waals heterostructure of magnetic insulator and graphene

Engineering two-dimensional material heterostructures by combining the best of different materials in one ultimate unit can offer a plethora of opportunities in condensed matter physics. Here, in the van der Waals heterostructures of the ferromagnetic insulator Cr2Ge2Te6 and graphene, our observations indicate an out-of-plane proximity-induced ferromagnetic exchange interaction in graphene. The perpendicular magnetic anisotropy of Cr2Ge2Te6 results in significant modification of the spin transport and precession in graphene, which is ascribed to the proximity-induced exchange interaction. Furthermore, the observation of a larger lifetime for perpendicular spins in comparison to the in-plane counterpart suggests the creation of a proximity-induced anisotropic spin texture in graphene. Our experimental results and density functional theory calculations open up opportunities for the realization of proximity-induced magnetic interactions and spin filters in 2D material heterostructures and can form the basic building blocks for future spintronic and topological quantum devices.

cond-mat.mes-hall↗

arXiv2019

Extraordinary efficient spin-orbit torque switching in (W, Ta)/epitaxial-Co60Fe40/TiN heterostructures

The giant spin Hall effect in magnetic heterostructures along with low spin memory loss and high interfacial spin mixing conductance are prerequisites to realize energy efficient spin torque based logic devices. We report giant spin Hall angle (SHA) of 28.67 (5.09) for W (Ta) interfaced epi- Co60Fe40/TiN structures. The spin-orbit torque switching current density (J_Crit) is as low as 1.82 (8.21) MA/cm2 in W (Ta)/Co60Fe40(t_CoFe)/TiN structures whose origin lies in the epitaxial interfaces. These structures also exhibit very low spin memory loss and high spin mixing conductance. These extraordinary values of SHA and therefore ultra-low J_Crit in semiconducting industry compatible epitaxial materials combinations open up a new direction for the realization of energy efficient spin logic devices by utilizing epitaxial interfaces.

cond-mat.mtrl-sci↗

arXiv2019

Spin pumping and spin torque in interfacial tailored Co2FeAl/\b{eta}-Ta layers

The Heusler ferromagnetic (FM) compound Co2FeAl interfaced with a high-spin orbit coupling non-magnetic (NM) layer is a promising candidate for energy efficient spin logic circuits. The circuit potential depends on the strength of angular momentum transfer across the FM/NM interface; hence, requiring low spin memory loss and high spin-mixing conductance. To highlight this issue, spin pumping and spin-transfer torque ferromagnetic resonance measurements have been performed on Co_2FeAl/β-Ta heterostructures tailored with Cu interfacial layers. The interface tailored structure yields an enhancement of the effective spin-mixing conductance. The interface transparency and spin memory loss corrected values of the spin-mixing conductance, spin Hall angle and spin diffusion length are found to be 3.40 \pm 0.01 \times 10^{19} m^{-2}, 0.029 \pm 0.003, and 2.3 \pm 0.5 nm, respectively. Furthermore, a high current modulation of the effective damping of around 2.1 % has been achieved at an applied current density of 1 \times 10^9 A/m^2 , which clearly indicates the potential of using this heterostructure for energy efficient control in spin devices

cond-mat.mtrl-sci↗

arXiv2019

Engineering of spin mixing conductance in Ru/FeCo/Ru interfaces: Effect of Re Doping

We have deposited polycrystalline Re doped $(Fe_{65}Co_{35})_{100-x}Re_{x}$ (0 $\leq$ x $\leq$ 12.6 at\%) thin films grown under identical conditions and sandwiched between thin layers of Ru in order to study the phenomenon of spin pumping as a function of Re concentration. In-plane and out-of-plane ferromagnetic resonance spectroscopy results show an enhancement of the Gilbert damping with an increase in Re doping. We found evidence of an increase in the real part of effective spin mixing conductance [Re($g^{\uparrow\downarrow}_{eff}$)] with the increase in Re doping of 6.6 at\%, while a decrease is evident at higher Re doping. The increase in Re($g^{\uparrow\downarrow}_{eff}$) can be linked to the Re doping induced change of the interface electronic structure in the non-magnetic Ru layer and the effect interfacial spin-orbit coupling has on the effective spin-mixing conductance. The lowest and highest values of Re($g^{\uparrow\downarrow}_{eff}$) are found to be 9.883(02) $nm^{-2}$ and 19.697(02) $nm^{-2}$ for 0 at\% and 6.6 at\% Re doping, respectively. The saturation magnetization decreases with increasing Re doping, from 2.362(13) T for the undoped film to 1.740(03) T for 12.6 at\% Re doping. This study opens a new direction of tuning the spin-mixing conductance in magnetic heterostructures by doping of the ferromagnetic layerr, which is essential for the realization of energy efficient operation of spintronic devices.

cond-mat.mtrl-sci↗

arXiv2019

Enhanced Gilbert Damping in Re doped FeCo Films: A Combined Experimental and Theoretical Study

The effects of rhenium doping in the range 0 to 10 atomic percent on the static and dynamic magnetic properties of Fe65Co35 thin films have been studied experimentally as well as with first principles electronic structure calculations focusing on the change of the saturation magnetization and the Gilbert damping parameter. Both experimental and theoretical results show that the saturation magnetization decreases with increasing Re doping level, while at the same time Gilbert damping parameter increases. The experimental low temperature saturation magnetic induction exhibits a 29 percent decrease, from 2.31 T to 1.64 T, in the investigated doping concentration range, which is more than predicted by the theoretical calculations. The room temperature value of the damping parameter obtained from ferromagnetic resonance measurements, correcting for extrinsic contributions to the damping, is for the undoped sample 0.0027, which is close to the theoretically calculated Gilbert damping parameter. With 10 atomic percent Re doping, the damping parameter increases to 0.0090, which is in good agreement with the theoretical value of 0.0073. The increase in damping parameter with Re doping is explained by the increase in density of states at Fermi level, mostly contributed by the spin-up channel of Re. Moreover, both experimental and theoretical values for the damping parameter are observed to be weakly decreasing with decreasing temperature.

cond-mat.mtrl-sci↗

arXiv2019

Collective magnetization dynamics in nano-arrays of thin FePd discs

We report on the magnetization dynamics of a square array of mesoscopic discs, fabricated from an iron palladium alloy film. The dynamics properties were explored using ferromagnetic resonance measurements and micromagnetic simulations. The obtained spectra exhibit features resulting from the interactions between the discs, with a clear dependence on both temperature and the direction of the externally applied field. We demonstrate a qualitative agreement between the measured and calculated spectra. Furthermore, we calculated the mode profiles of the standing spin waves excited during a time-dependent magnetic field excitations. The resulting maps confirm that the features appearing in the ferromagnetic resonance absorption spectra originate from the temperature and directional dependent inter-disc interactions.

cond-mat.mes-hall↗

arXiv2018

Non-Reciprocal Spin Pumping in Asymmetric Magnetic Trilayers

In magnetic trilayer systems, spin pumping is generally addressed as a reciprocal mechanism characterized by one unique spin mixing conductance common to both interfaces. However, this assumption is questionable in cases where different types of interfaces are present in the material. Here, we present a general theory for analyzing spin pumping in cases with more than one unique interface. The theory is applied to analyze layer-resolved ferromagnetic resonance experiments on the trilayer system Ni$_{20}$Fe$_{80}$/Ru/Fe$_{49}$Co$_{49}$V$_2$ where the Ru spacer thickness is varied to tune the indirect exchange coupling. The results show that the spin pumping in trilayer systems with dissimilar magnetic layers is non-reciprocal, with a surprisingly large difference between spin-pumping induced damping of different interfaces. Our findings have importance on dynamics of spintronic devices based on magnetic multilayer materials.

cond-mat.mes-hall↗

arXiv2018

Magnetocrystalline anisotropy of Fe5PB2 and its alloys with Co and 5d elements: a combined first-principles and experimental study

The Fe$_5$PB$_2$ compound offers tunable magnetic properties via the possibility of various combinations of substitutions on the Fe and P-sites. Here, we present a combined computational and experimental study of the magnetic properties of (Fe$_{1-x}$Co$_{x}$)$_5$PB$_2$. Computationally, we are able to explore the full concentration range, while the real samples were only obtained for 0 <= x <= 0.7. The calculated magnetic moments, Curie temperatures, and magnetocrystalline anisotropy energies (MAEs) are found to decrease with increasing Co concentration. Co substitution allows for tuning the Curie temperature in a wide range of values, from about six hundred to zero kelvins. As the MAE depends on the electronic structure in the vicinity of Fermi energy, the geometry of the Fermi surface of Fe$_5$PB$_2$ and the k-resolved contributions to the MAE are discussed. Low temperature measurements of an effective anisotropy constant for a series of (Fe$_{1-x}$Co$_{x}$)$_5$PB$_2$ samples determined the highest value of 0.94 MJ m$^{-3}$ for the terminal Fe$_5$PB$_2$ composition, which then decreases with increasing Co concentration, thus confirming the computational result that Co alloying of Fe$_5$PB$_2$ is not a good strategy to increase the MAE of the system. However, the relativistic version of the fixed spin moment method reveals that a reduction in the magnetic moment of Fe$_5$PB$_2$, by about 25%, produces a fourfold increase of the MAE. Furthermore, calculations for (Fe$_{0.95}$X$_{0.05}$)$_5$PB$_2$ (X = 5$d$ element) indicate that 5% doping of Fe$_5$PB$_2$ with W or Re should double the MAE. These are results of high interest for, e.g., permanent magnet applications, where a large MAE is crucial.

cond-mat.mtrl-sci↗

arXiv2018

Revisiting Goodenough-Kanamori rules in a new series of double perovskites LaSr$_{1-x}$Ca$_x$NiReO$_6$

The magnetic ground state in highly ordered double perovskites LaSr$_{1-x}$Ca$_x$NiReO$_6$ ($x$ = 0.0, 0.5, 1.0) were studied in view of the Goodenough-Kanamori rules of superexchange interactions. In LaSrNiReO$_6$, Ni and Re sublattices are found to exhibit curious magnetic states, but do not show any long range magnetic ordering. The magnetic transition at $\sim$ 255 K is identified with the Re sublattic magnetic ordering. The sublattice interactions are tuned by modifying the Ni-O-Re bond angles via changing the lattice structure through Ca doping. Upon Ca doping, the Ni and Re sublattices start to display a ferrimagnetically ordered state at low temperature. The neutron powder diffraction reveals a canted alignment between the Ni and the Re sublattices, while the individual sublattice is ferromagnetic. The transition temperature of the ferrimagnetic phase increases monotonically with increasing Ca concentration.

cond-mat.str-el↗

arXiv2018

Exchange dependent ultrafast magnetization dynamics in Fe$_{1-x}$Ni$_{x}$ alloys

Element specific ultrafast demagnetization was studied in Fe$_{1-x}$Ni$_{x}$ alloys, covering the concentration range between $0.1<x<0.9$. For all compositions, we observe a delay in the onset of Ni demagnetization relative to the Fe demagnetization. We find that the delay is correlated to the Curie temperature and hence also the exchange interaction. The temporal evolution of demagnetization is fitted to a magnon diffusion model based on the presupposition of enhanced ultrafast magnon generation in the Fe sublattice. The spin wave stiffness extracted from this model correspond well to known experimental values.

cond-mat.mtrl-sci↗

arXiv2018

Effect of in-situ electric field assisted growth on anti-phase boundaries in epitaxial Fe3O4 thin films on MgO

Anti-phase boundaries (APBs) normally form as a consequence of the initial growth conditions in all spinel ferrite thin films. The presence of APBs in epitaxial films of the inverse spinel Fe3O4 alters their electronic and magnetic properties due to strong antiferromagnetic (AF) interactions across these boundaries. The effect of using in-situ electric field assisted growth on the migration of APBs in hetero epitaxial Fe3O4(100)/MgO(100) thin films have been explored in the present work. The electric field assisted growth is found to reduce the AF interactions across APBs and as a consequence APBs free thin film like properties are obtained, which have been probed by electronic, magnetic and structural characterization. An increase in energy associated with the nucleation and/or early stage of the growth and, therefore, a corresponding increase in surface mobility of the ad-atoms play a critical role in controlling the density of APBs. This innovative technique can be employed to grow epitaxial spinel thin films with controlled AF interactions across APBs.

cond-mat.mtrl-sci↗

arXiv2017

Spin Pumping in Ion-beam Sputtered Co_{2}FeAl/Mo Bilayers:Interfacial Gilbert Damping

The spin pumping mechanism and associated interfacial Gilbert damping are demonstrated in ion-beam sputtered Co2FeAl (CFA) /Mo bilayer thin films employing ferromagnetic resonance spectroscopy. The dependence of the net spin current transportation on Mo layer thickness, 0 to 10 nm, and the enhancement of the net effective Gilbert damping are reported. The experimental data has been analyzed using spin pumping theory in terms of spin current pumped through the ferromagnet /nonmagnetic metal interface to deduce the effective spin mixing conductance and the spin-diffusion length, which are estimated to be 1.16(0.19)x10^19 m^-2 and 3.50(0.35)nm, respectively. The damping constant is found to be 8.4(0.3)x10^-3 in the Mo(3.5nm) capped CFA(8nm) sample corresponding to a ~42% enhancement of the original Gilbert damping (6.0(0.3)x10^-3) in the uncapped CFA layer. This is further confirmed by inserting a Cu dusting layer which reduces the spin transport across the CFA /Mo interface. The Mo layer thickness dependent net spin current density is found to lie in the range of 1-3 MAm^-2, which also provides additional quantitative evidence of spin pumping in this bilayer thin film system.

cond-mat.mes-hall↗