We employed micro-focused Brillouin light scattering to study the amplification of the thermal sp... more We employed micro-focused Brillouin light scattering to study the amplification of the thermal spin wave eigenmodes by means of a pure spin current, generated by the spin-Hall effect, in a transversely magnetized Pt(4 nm)/NiFe(4 nm)/SiO 2 (5 nm) layered nanowire with lateral dimensions 500 Â 2750 nm 2 . The frequency and the cross section of both the center (fundamental) and the edge spin wave modes have been measured as a function of the intensity of the injected dc electric current. The frequency of both modes exhibits a clear redshift while their cross section is greatly enhanced on increasing the intensity of the injected dc. A threshold-like behavior is observed for a value of the injected dc of 2.8 mA. Interestingly, an additional mode, localized in the central part of the nanowire, appears at higher frequency on increasing the intensity of the injected dc above the threshold value. Micromagnetic simulations were used to quantitatively reproduce the experimental results and to investigate the complex non-linear dynamics induced by the spin-Hall effect, including the modification of the spatial profile of the spin wave modes and the appearance of the extra mode above the threshold. V C 2015 AIP Publishing LLC.[http://dx.
Fe/ZnSe(001) system is attracting interest because it is one of the rare successful example of fe... more Fe/ZnSe(001) system is attracting interest because it is one of the rare successful example of ferromagnetic metal–semiconductor epitaxy, where both chemistry and magnetic properties of the interfaces remain stables up to 600K. This can be very important in view of the production of spintronics devices. Epitaxial Fe films with thickness in the range between 0.7 and 5nm were deposited on
We report spin wave excitations in a nanopatterned antidot lattice fabricated from a 30-nm thick ... more We report spin wave excitations in a nanopatterned antidot lattice fabricated from a 30-nm thick Ni 80 Fe 20 film. The 250-nm-wide circular holes are arranged in a rhombic unit cell with a lattice constant of 400 nm. By Brillouin light scattering, we find that quantized spin wave modes transform to propagating ones and vice versa by changing the in-plane orientation of the applied magnetic field H by 30 • . Spin waves of either negative or positive group velocity are found. In the latter case, they propagate in narrow channels exhibiting a width of below 100 nm. We use the plane wave method to calculate the spin wave dispersions for the two relevant orientations of H. The theory allows us to explain the wave-vector-dependent characteristics of the prominent modes. Allowed minibands are formed for selected modes only for specific orientations of H and wave vector. The results are important for applications such as spin wave filters and interconnected waveguides in the emerging field of magnonics where the control of spin wave propagation on the nanoscale is key.
We present a Brillouin light scattering investigation of the eigenmode spectrum of nanometric per... more We present a Brillouin light scattering investigation of the eigenmode spectrum of nanometric permalloy rings as a function of the applied magnetic field. In particular, different splitting effects induced by the applied magnetic field on the radial and azimuthal excitations have been observed and explained in terms of either mode localization or symmetry. The dynamical matrix approach has been used
The field-driven reorientation transition of an anisotropic ferromagnetic monolayer is studied wi... more The field-driven reorientation transition of an anisotropic ferromagnetic monolayer is studied within the context of a finite-temperature Green's function theory. The equilibrium state and the field dependence of the magnon energy gap E0 are calculated for static magnetic field H applied in plane along an easy or a hard axis. In the latter case, the in-plane reorientation of the magnetization is shown to be continuous at T = 0, in agreement with free spin wave theory, and discontinuous at finite temperature T > 0, in contrast with the prediction of mean field theory. The discontinuity in the orientation angle creates a jump in the magnon energy gap, and it is the reason why, for T > 0, the energy does not go to zero at the reorientation field. Above the Curie temperature TC, the magnon energy gap E0(H) vanishes for H = 0 both in the easy and in the hard case. As H is increased, the gap is found to increase almost linearly with H, but with different slopes depending on the field orientation. In particular, the slope is smaller when H is along the hard axis. Such a magnetic anisotropy of the spin wave energies is shown to persist well above TC (T ≈ 1.2 TC ).
The frequencies of spin wave eigenmodes of square permalloy nano-elements with relatively large a... more The frequencies of spin wave eigenmodes of square permalloy nano-elements with relatively large aspect ratio (thickness 20 nm, width 275 nm), fabricated by deep ultraviolet lithography, were measured experimentally using Brillouin light scattering (BLS). The measurements were done in a wide range of bias magnetic fields applied along one of the in-plane sides of the square element. The experimental data have been reproduced using both micromagnetic and analytical calculations, which allowed us to reliably identify the spatial structure of the excited spin wave eigenmodes. It is demonstrated that both purely dipolar sinusoidal and dipole-exchange localized spin wave eigenmodes contribute to the formation of the discrete BLS spectrum of the nano-element. r
We present an experimental investigation of the magnetization reversal process in NiFe/Cu(10 nm)/... more We present an experimental investigation of the magnetization reversal process in NiFe/Cu(10 nm)/Co circular and elliptical nano-elements with different thickness of the magnetic layers. The results obtained using element sensitive X-ray resonant magnetic scattering (XRMS) were compared with the previous measurements showing that the dipolar interlayer coupling favours the antiparallel alignment of the two magnetization layers at remanance. In the case of circular shape, the increased thickness of the ferromagnetic layers stabilizes the antiparallel alignment of the layers over a wider field range. A similar effect, accompanied by a delay in the onset of the antiparallel alignment, is observed in the case of elliptical nano-elements and applying the external field along the longer axis of the elements, due to the additional shape anisotropy.
We present an experimental investigation of the static and dynamical properties of array of Ni80F... more We present an experimental investigation of the static and dynamical properties of array of Ni80Fe20 (10 nm)/Cu (10 nm)/Co (10 nm) disks with diameter of 230 nm and edge-to-edge spacing of 160 nm. Magnetization reversal process studied by superconducting quantum interference device magnetometry, resonant scattering of polarized soft x-ray, and three-dimensional micromagnetic simulations reveals that the interlayer magnetostatic interaction and the different coercivities of the two layers are the key factors that determine the magnetization reversal of the disks through a sequence of antiparallel states. The dynamical properties were studied by Brillouin light scattering and micromagnetic simulations which solve the discretized Landau-Lifshitz-Gilbert equation in the time domain and calculated locally the Fourier transform. The comparison between measurements and simulations allowed us to correlate the field dependence of different modes in each ferromagnetic layer to their localization inside the disk.
We present an experimental study of the static and high frequency dynamic properties of NiFe͑10 n... more We present an experimental study of the static and high frequency dynamic properties of NiFe͑10 nm͒ / Cu͑t Cu ͒ / Co͑10 nm͒ nanometric disks for different values of the Cu spacer thickness ͑t Cu = 0.7, 1.2, and 2.0 nm͒. We found that the exchange interlayer coupling dominates over the dipolar interaction favoring parallel alignment between the two layers of magnetization with formation of vortex states at remanence. Brillouin light scattering technique from thermally excited spin waves was used to estimate the value of the interlayer exchange coupling in the unpatterned NiFe/Cu/Co films as well as to investigate the magnetic normal modes in the corresponding multilayered nanodisks. In the latter case, evidence is given for a discretization of the measured spectrum with reduction in the mode frequency associated to the demagnetizing effect induced by lateral confinement. Micromagnetic simulations indicate that these discrete modes correspond to an in-phase precession of the magnetization in the two ferromagnetic layers while, at variance with the continuous film, no evidence of optical modes is obtained.
The dependence of the interlayer coupling on both the soft (FeTaN) and hard (FeSm) layer thicknes... more The dependence of the interlayer coupling on both the soft (FeTaN) and hard (FeSm) layer thickness in FeTaN-FeSm-FeTaN multilayers, deposited by dc magnetron sputtering, has been investigated. The magnetization reversal process is examined experimentally using a magnetooptical Kerr effect. The exchange field ex , which is a measure of the average coupling between the soft and hard layers, was determined from the field shift of the minor hysteresis loop. The value of ex increases as the number of the soft FeTaN layer increases. A significant and fully reversible transverse hysteresis loop was measured indicating that, during the magnetization-reversal process, the magnetic moments in the soft layers rotate reversibly, as typical of exchange-spring systems.
... 390 Properties of CoFe Films: Dependence of Cathode Potentials M. Alper, H. Kockar, T. Sahin... more ... 390 Properties of CoFe Films: Dependence of Cathode Potentials M. Alper, H. Kockar, T. Sahin, and O. Karaagac 393 Thermal and Magnetic Properties in (FeBSi)NbY Bulk Glassy Alloys R. Piccin, M. Baricco, P. Tiberto, N. Lupu, and H. Chiriac ...
ABSTRACT Exchange spring magnets, consisting of a [Co(0.5 nm)/Pd(1 nm)]5 multilayer with perpendi... more ABSTRACT Exchange spring magnets, consisting of a [Co(0.5 nm)/Pd(1 nm)]5 multilayer with perpendicular magnetic anisotropy and a Co20Fe60B20 film with easy plane anisotropy, of variable thickness t CFB, are investigated using Brillouin light scattering. On reducing t CFB in the range 0.8–2.3 nm, the spin-wave frequency gap displays a remarkable increase from nearly 4–48 GHz, reflecting the corresponding rapid growth of the tilting angle of the magnetization with respect to the film normal. These findings are interpreted using a one-dimensional model in which each atomic layer is assumed to be uniformly magnetized, subjected to an effective out-of-plane or easy-plane anisotropy depending on the layer position in the stack, and exchange coupled to its two nearest neighbour atomic layers. With respect to previously investigated [Co/Pd]-NiFe hybrid magnets, a largest frequency tunability, restricted to a narrower range of the soft layer thickness, is observed.
We employed micro-focused Brillouin light scattering to study the amplification of the thermal sp... more We employed micro-focused Brillouin light scattering to study the amplification of the thermal spin wave eigenmodes by means of a pure spin current, generated by the spin-Hall effect, in a transversely magnetized Pt(4 nm)/NiFe(4 nm)/SiO 2 (5 nm) layered nanowire with lateral dimensions 500 Â 2750 nm 2 . The frequency and the cross section of both the center (fundamental) and the edge spin wave modes have been measured as a function of the intensity of the injected dc electric current. The frequency of both modes exhibits a clear redshift while their cross section is greatly enhanced on increasing the intensity of the injected dc. A threshold-like behavior is observed for a value of the injected dc of 2.8 mA. Interestingly, an additional mode, localized in the central part of the nanowire, appears at higher frequency on increasing the intensity of the injected dc above the threshold value. Micromagnetic simulations were used to quantitatively reproduce the experimental results and to investigate the complex non-linear dynamics induced by the spin-Hall effect, including the modification of the spatial profile of the spin wave modes and the appearance of the extra mode above the threshold. V C 2015 AIP Publishing LLC.[http://dx.
Fe/ZnSe(001) system is attracting interest because it is one of the rare successful example of fe... more Fe/ZnSe(001) system is attracting interest because it is one of the rare successful example of ferromagnetic metal–semiconductor epitaxy, where both chemistry and magnetic properties of the interfaces remain stables up to 600K. This can be very important in view of the production of spintronics devices. Epitaxial Fe films with thickness in the range between 0.7 and 5nm were deposited on
We report spin wave excitations in a nanopatterned antidot lattice fabricated from a 30-nm thick ... more We report spin wave excitations in a nanopatterned antidot lattice fabricated from a 30-nm thick Ni 80 Fe 20 film. The 250-nm-wide circular holes are arranged in a rhombic unit cell with a lattice constant of 400 nm. By Brillouin light scattering, we find that quantized spin wave modes transform to propagating ones and vice versa by changing the in-plane orientation of the applied magnetic field H by 30 • . Spin waves of either negative or positive group velocity are found. In the latter case, they propagate in narrow channels exhibiting a width of below 100 nm. We use the plane wave method to calculate the spin wave dispersions for the two relevant orientations of H. The theory allows us to explain the wave-vector-dependent characteristics of the prominent modes. Allowed minibands are formed for selected modes only for specific orientations of H and wave vector. The results are important for applications such as spin wave filters and interconnected waveguides in the emerging field of magnonics where the control of spin wave propagation on the nanoscale is key.
We present a Brillouin light scattering investigation of the eigenmode spectrum of nanometric per... more We present a Brillouin light scattering investigation of the eigenmode spectrum of nanometric permalloy rings as a function of the applied magnetic field. In particular, different splitting effects induced by the applied magnetic field on the radial and azimuthal excitations have been observed and explained in terms of either mode localization or symmetry. The dynamical matrix approach has been used
The field-driven reorientation transition of an anisotropic ferromagnetic monolayer is studied wi... more The field-driven reorientation transition of an anisotropic ferromagnetic monolayer is studied within the context of a finite-temperature Green's function theory. The equilibrium state and the field dependence of the magnon energy gap E0 are calculated for static magnetic field H applied in plane along an easy or a hard axis. In the latter case, the in-plane reorientation of the magnetization is shown to be continuous at T = 0, in agreement with free spin wave theory, and discontinuous at finite temperature T > 0, in contrast with the prediction of mean field theory. The discontinuity in the orientation angle creates a jump in the magnon energy gap, and it is the reason why, for T > 0, the energy does not go to zero at the reorientation field. Above the Curie temperature TC, the magnon energy gap E0(H) vanishes for H = 0 both in the easy and in the hard case. As H is increased, the gap is found to increase almost linearly with H, but with different slopes depending on the field orientation. In particular, the slope is smaller when H is along the hard axis. Such a magnetic anisotropy of the spin wave energies is shown to persist well above TC (T ≈ 1.2 TC ).
The frequencies of spin wave eigenmodes of square permalloy nano-elements with relatively large a... more The frequencies of spin wave eigenmodes of square permalloy nano-elements with relatively large aspect ratio (thickness 20 nm, width 275 nm), fabricated by deep ultraviolet lithography, were measured experimentally using Brillouin light scattering (BLS). The measurements were done in a wide range of bias magnetic fields applied along one of the in-plane sides of the square element. The experimental data have been reproduced using both micromagnetic and analytical calculations, which allowed us to reliably identify the spatial structure of the excited spin wave eigenmodes. It is demonstrated that both purely dipolar sinusoidal and dipole-exchange localized spin wave eigenmodes contribute to the formation of the discrete BLS spectrum of the nano-element. r
We present an experimental investigation of the magnetization reversal process in NiFe/Cu(10 nm)/... more We present an experimental investigation of the magnetization reversal process in NiFe/Cu(10 nm)/Co circular and elliptical nano-elements with different thickness of the magnetic layers. The results obtained using element sensitive X-ray resonant magnetic scattering (XRMS) were compared with the previous measurements showing that the dipolar interlayer coupling favours the antiparallel alignment of the two magnetization layers at remanance. In the case of circular shape, the increased thickness of the ferromagnetic layers stabilizes the antiparallel alignment of the layers over a wider field range. A similar effect, accompanied by a delay in the onset of the antiparallel alignment, is observed in the case of elliptical nano-elements and applying the external field along the longer axis of the elements, due to the additional shape anisotropy.
We present an experimental investigation of the static and dynamical properties of array of Ni80F... more We present an experimental investigation of the static and dynamical properties of array of Ni80Fe20 (10 nm)/Cu (10 nm)/Co (10 nm) disks with diameter of 230 nm and edge-to-edge spacing of 160 nm. Magnetization reversal process studied by superconducting quantum interference device magnetometry, resonant scattering of polarized soft x-ray, and three-dimensional micromagnetic simulations reveals that the interlayer magnetostatic interaction and the different coercivities of the two layers are the key factors that determine the magnetization reversal of the disks through a sequence of antiparallel states. The dynamical properties were studied by Brillouin light scattering and micromagnetic simulations which solve the discretized Landau-Lifshitz-Gilbert equation in the time domain and calculated locally the Fourier transform. The comparison between measurements and simulations allowed us to correlate the field dependence of different modes in each ferromagnetic layer to their localization inside the disk.
We present an experimental study of the static and high frequency dynamic properties of NiFe͑10 n... more We present an experimental study of the static and high frequency dynamic properties of NiFe͑10 nm͒ / Cu͑t Cu ͒ / Co͑10 nm͒ nanometric disks for different values of the Cu spacer thickness ͑t Cu = 0.7, 1.2, and 2.0 nm͒. We found that the exchange interlayer coupling dominates over the dipolar interaction favoring parallel alignment between the two layers of magnetization with formation of vortex states at remanence. Brillouin light scattering technique from thermally excited spin waves was used to estimate the value of the interlayer exchange coupling in the unpatterned NiFe/Cu/Co films as well as to investigate the magnetic normal modes in the corresponding multilayered nanodisks. In the latter case, evidence is given for a discretization of the measured spectrum with reduction in the mode frequency associated to the demagnetizing effect induced by lateral confinement. Micromagnetic simulations indicate that these discrete modes correspond to an in-phase precession of the magnetization in the two ferromagnetic layers while, at variance with the continuous film, no evidence of optical modes is obtained.
The dependence of the interlayer coupling on both the soft (FeTaN) and hard (FeSm) layer thicknes... more The dependence of the interlayer coupling on both the soft (FeTaN) and hard (FeSm) layer thickness in FeTaN-FeSm-FeTaN multilayers, deposited by dc magnetron sputtering, has been investigated. The magnetization reversal process is examined experimentally using a magnetooptical Kerr effect. The exchange field ex , which is a measure of the average coupling between the soft and hard layers, was determined from the field shift of the minor hysteresis loop. The value of ex increases as the number of the soft FeTaN layer increases. A significant and fully reversible transverse hysteresis loop was measured indicating that, during the magnetization-reversal process, the magnetic moments in the soft layers rotate reversibly, as typical of exchange-spring systems.
... 390 Properties of CoFe Films: Dependence of Cathode Potentials M. Alper, H. Kockar, T. Sahin... more ... 390 Properties of CoFe Films: Dependence of Cathode Potentials M. Alper, H. Kockar, T. Sahin, and O. Karaagac 393 Thermal and Magnetic Properties in (FeBSi)NbY Bulk Glassy Alloys R. Piccin, M. Baricco, P. Tiberto, N. Lupu, and H. Chiriac ...
ABSTRACT Exchange spring magnets, consisting of a [Co(0.5 nm)/Pd(1 nm)]5 multilayer with perpendi... more ABSTRACT Exchange spring magnets, consisting of a [Co(0.5 nm)/Pd(1 nm)]5 multilayer with perpendicular magnetic anisotropy and a Co20Fe60B20 film with easy plane anisotropy, of variable thickness t CFB, are investigated using Brillouin light scattering. On reducing t CFB in the range 0.8–2.3 nm, the spin-wave frequency gap displays a remarkable increase from nearly 4–48 GHz, reflecting the corresponding rapid growth of the tilting angle of the magnetization with respect to the film normal. These findings are interpreted using a one-dimensional model in which each atomic layer is assumed to be uniformly magnetized, subjected to an effective out-of-plane or easy-plane anisotropy depending on the layer position in the stack, and exchange coupled to its two nearest neighbour atomic layers. With respect to previously investigated [Co/Pd]-NiFe hybrid magnets, a largest frequency tunability, restricted to a narrower range of the soft layer thickness, is observed.
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Papers by Marco Madami