R. Adur - Academia.edu (original) (raw)

Papers by R. Adur

) material without an accompanying charge current [1-4]. It is widely believed that this pumping ... more ) material without an accompanying charge current [1-4]. It is widely believed that this pumping proceeds exclusively via a short-range exchange interaction at the FM/NM interface [4]. Here we report robust, long-range spin pumping from the ferrimagnetic double perovskite Sr 2 FeMoO 6 (SFMO) into Pt across an insulating barrier up to 200 nm thick, and systematically rule out all known spurious effects. This result demonstrates dynamic spin injection over a distance far beyond the coupling range of the exchange interaction, exposing the need to consider other coupling mechanisms. The characteristic length scale for magnetic textures in Sr 2 FeMoO 6 is approximately 150 nm, resulting from structural antiphase boundaries [5], thus raising the possibility that magnetic dipole coupling underlies the observed long range spin transfer. This discovery reveals a route to dynamic angular momentum transfer between a FM and a NM in the absence of mediation by itinerant electrons and promises new spin-functional devices employing long-range spin pumping.

Applied Physics Letters, 2014

ABSTRACT We present the growth of thin films of the organic-based ferrimagnetic semiconductor V[T... more ABSTRACT We present the growth of thin films of the organic-based ferrimagnetic semiconductor V[TCNE]x (x ∼ 2, TCNE: tetracyanoethylene) via chemical vapor deposition. Under optimized growth conditions, we observe a significant increase in magnetic homogeneity, as evidenced by a Curie temperature above 600 K and sharp magnetization switching. Further, ferromagnetic resonance studies reveal a single resonance with full width at half maximum linewidth of 1.4 G, comparable to the narrowest lines measured in inorganic magnetic materials and in contrast to previous studies that showed multiple resonance features. These characteristics are promising for the development of high frequency electronic devices that take advantage of the unique properties of this organic-based material, such as the potential for low cost synthesis combined with low temperature and conformal deposition on a wide variety of substrates.

Physical Review Letters, 2014

We have investigated spin pumping from Y3Fe5O12 thin films into Cu, Ag, Ta, W, Pt, and Au with va... more We have investigated spin pumping from Y3Fe5O12 thin films into Cu, Ag, Ta, W, Pt, and Au with varying spin-orbit coupling strengths. From measurements of Gilbert damping enhancement and inverse spin Hall signals spanning 3 orders of magnitude, we determine the spin Hall angles and interfacial spin mixing conductances for the six metals. The spin Hall angles largely vary as Z(4) (Z: atomic number), corroborating the role of spin-orbit coupling. Amongst the four 5d metals, the variation of the spin Hall angle is dominated by the sensitivity of the d-orbital moment to the d-electron count, confirming theoretical predictions.

Journal of Applied Physics, 2014

Ferromagnetic resonance (FMR) spin pumping is a rapidly growing field which has demonstrated prom... more Ferromagnetic resonance (FMR) spin pumping is a rapidly growing field which has demonstrated promising results in a variety of material systems. This technique utilizes the resonant precession of magnetization in a ferromagnet to inject spin into an adjacent non-magnetic material. Spin pumping into graphene is attractive on account of its exceptional spin transport properties. This article reports on FMR characterization of cobalt grown on CVD graphene and examines the validity of linewidth broadening as an indicator of spin pumping. In comparison to cobalt samples without graphene, direct contact cobalt-on-graphene exhibits increased FMR linewidth-an often used signature of spin pumping. Similar results are obtained in Co/MgO/graphene structures, where a 1nm MgO layer acts as a tunnel barrier. However, SQUID, MFM, and Kerr microscopy measurements demonstrate increased magnetic disorder in cobalt grown on graphene, perhaps due to changes in the growth process and an increase in defects. This magnetic disorder may account for the observed linewidth enhancement due to effects such as two-magnon scattering or mosaicity. As such, it is not possible to conclude successful spin injection into graphene from FMR linewidth measurements alone.

ABSTRACT The recent demonstration of the injection of a pure spin current via ferromagnetic reson... more ABSTRACT The recent demonstration of the injection of a pure spin current via ferromagnetic resonance (FMR) in the FM electrode, spin-pumping, with no need for an accompanying charge current, promises low-power high-efficiency spin injection in a wide variety of materials. Here we report the demonstration of FMR spin-pumping in Ferromagnet/Insulator/Non-magnetic materials heterostructures via different spin detection techniques, and characterizations of the dynamically injected spin. Our investigation proves the possibility that one can both utilize the advantages of FMR spin-pumping, and simultaneously overcome the well-known resistance mismatch problem, which usually happens for spin injection through a FM/NM direct contact and drastically suppresses the efficiency of spin injection into NM. Furthermore, by individually and systematically varying the magnetic, electrical and mechanical properties of each element of the FM/I/NM heterostructures, we are able to study the fundamental mechanisms for FMR spin-pumping, e.g. coupling range and strength, and role of and interplay between spin, charge, lattice, magnon and phonon degree of freedoms.

IEEE Transactions on Magnetics, 2000

ABSTRACT The high-frequency response of magneto-optic ferrites for field-sensing applications is ... more ABSTRACT The high-frequency response of magneto-optic ferrites for field-sensing applications is dictated by the ferromagnetic resonance (FMR) frequency. The FMR frequency can be increased by applying an external biasing field or by tuning the internal anisotropies of the material to provide a self-bias. We report the angular dependence of FMR spectra of bismuth-substituted rare-earth iron garnet thin films to extract their uniaxial and cubic anisotropies. These measurements allow us to estimate the characteristic resonant frequency in the self-bias regime, which is equivalent to the high-frequency limit for magnetic field-sensing in these materials when no external field is applied. We find that the frequency limit estimated by FMR agrees with the measured frequency limit of a magneto-optic field sensor utilizing the same garnet composition.

) material without an accompanying charge current [1-4]. It is widely believed that this pumping ... more ) material without an accompanying charge current [1-4]. It is widely believed that this pumping proceeds exclusively via a short-range exchange interaction at the FM/NM interface [4]. Here we report robust, long-range spin pumping from the ferrimagnetic double perovskite Sr 2 FeMoO 6 (SFMO) into Pt across an insulating barrier up to 200 nm thick, and systematically rule out all known spurious effects. This result demonstrates dynamic spin injection over a distance far beyond the coupling range of the exchange interaction, exposing the need to consider other coupling mechanisms. The characteristic length scale for magnetic textures in Sr 2 FeMoO 6 is approximately 150 nm, resulting from structural antiphase boundaries [5], thus raising the possibility that magnetic dipole coupling underlies the observed long range spin transfer. This discovery reveals a route to dynamic angular momentum transfer between a FM and a NM in the absence of mediation by itinerant electrons and promises new spin-functional devices employing long-range spin pumping.

Applied Physics Letters, 2014

ABSTRACT We present the growth of thin films of the organic-based ferrimagnetic semiconductor V[T... more ABSTRACT We present the growth of thin films of the organic-based ferrimagnetic semiconductor V[TCNE]x (x ∼ 2, TCNE: tetracyanoethylene) via chemical vapor deposition. Under optimized growth conditions, we observe a significant increase in magnetic homogeneity, as evidenced by a Curie temperature above 600 K and sharp magnetization switching. Further, ferromagnetic resonance studies reveal a single resonance with full width at half maximum linewidth of 1.4 G, comparable to the narrowest lines measured in inorganic magnetic materials and in contrast to previous studies that showed multiple resonance features. These characteristics are promising for the development of high frequency electronic devices that take advantage of the unique properties of this organic-based material, such as the potential for low cost synthesis combined with low temperature and conformal deposition on a wide variety of substrates.

Physical Review Letters, 2014

We have investigated spin pumping from Y3Fe5O12 thin films into Cu, Ag, Ta, W, Pt, and Au with va... more We have investigated spin pumping from Y3Fe5O12 thin films into Cu, Ag, Ta, W, Pt, and Au with varying spin-orbit coupling strengths. From measurements of Gilbert damping enhancement and inverse spin Hall signals spanning 3 orders of magnitude, we determine the spin Hall angles and interfacial spin mixing conductances for the six metals. The spin Hall angles largely vary as Z(4) (Z: atomic number), corroborating the role of spin-orbit coupling. Amongst the four 5d metals, the variation of the spin Hall angle is dominated by the sensitivity of the d-orbital moment to the d-electron count, confirming theoretical predictions.

Journal of Applied Physics, 2014

Ferromagnetic resonance (FMR) spin pumping is a rapidly growing field which has demonstrated prom... more Ferromagnetic resonance (FMR) spin pumping is a rapidly growing field which has demonstrated promising results in a variety of material systems. This technique utilizes the resonant precession of magnetization in a ferromagnet to inject spin into an adjacent non-magnetic material. Spin pumping into graphene is attractive on account of its exceptional spin transport properties. This article reports on FMR characterization of cobalt grown on CVD graphene and examines the validity of linewidth broadening as an indicator of spin pumping. In comparison to cobalt samples without graphene, direct contact cobalt-on-graphene exhibits increased FMR linewidth-an often used signature of spin pumping. Similar results are obtained in Co/MgO/graphene structures, where a 1nm MgO layer acts as a tunnel barrier. However, SQUID, MFM, and Kerr microscopy measurements demonstrate increased magnetic disorder in cobalt grown on graphene, perhaps due to changes in the growth process and an increase in defects. This magnetic disorder may account for the observed linewidth enhancement due to effects such as two-magnon scattering or mosaicity. As such, it is not possible to conclude successful spin injection into graphene from FMR linewidth measurements alone.

ABSTRACT The recent demonstration of the injection of a pure spin current via ferromagnetic reson... more ABSTRACT The recent demonstration of the injection of a pure spin current via ferromagnetic resonance (FMR) in the FM electrode, spin-pumping, with no need for an accompanying charge current, promises low-power high-efficiency spin injection in a wide variety of materials. Here we report the demonstration of FMR spin-pumping in Ferromagnet/Insulator/Non-magnetic materials heterostructures via different spin detection techniques, and characterizations of the dynamically injected spin. Our investigation proves the possibility that one can both utilize the advantages of FMR spin-pumping, and simultaneously overcome the well-known resistance mismatch problem, which usually happens for spin injection through a FM/NM direct contact and drastically suppresses the efficiency of spin injection into NM. Furthermore, by individually and systematically varying the magnetic, electrical and mechanical properties of each element of the FM/I/NM heterostructures, we are able to study the fundamental mechanisms for FMR spin-pumping, e.g. coupling range and strength, and role of and interplay between spin, charge, lattice, magnon and phonon degree of freedoms.

IEEE Transactions on Magnetics, 2000

ABSTRACT The high-frequency response of magneto-optic ferrites for field-sensing applications is ... more ABSTRACT The high-frequency response of magneto-optic ferrites for field-sensing applications is dictated by the ferromagnetic resonance (FMR) frequency. The FMR frequency can be increased by applying an external biasing field or by tuning the internal anisotropies of the material to provide a self-bias. We report the angular dependence of FMR spectra of bismuth-substituted rare-earth iron garnet thin films to extract their uniaxial and cubic anisotropies. These measurements allow us to estimate the characteristic resonant frequency in the self-bias regime, which is equivalent to the high-frequency limit for magnetic field-sensing in these materials when no external field is applied. We find that the frequency limit estimated by FMR agrees with the measured frequency limit of a magneto-optic field sensor utilizing the same garnet composition.