| 1. |
- Madami, M., et al.
(författare)
-
Propagating spin waves excited by spin-transfer torque: A combined electrical and optical study
- 2015
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 2469-9950 .- 2469-9969 .- 1550-235X. ; 92:2
-
Tidskriftsartikel (refereegranskat)abstract
- Nanocontact spin-torque oscillators are devices in which the generation of propagating spin waves can be sustained by spin transfer torque. In the present paper, we perform combined electrical and optical measurements in a single experimental setup to systematically investigate the excitation of spin waves by a nanocontact spin-torque oscillator and their propagation in a Ni80Fe20 extended layer. By using microfocused Brillouin light scattering we observe an anisotropic emission of spin waves, due to the broken symmetry imposed by the inhomogeneous Oersted field generated by the injected current. In particular, spin waves propagate on the side of the nanocontact where the Oersted field and the in-plane component of the applied magnetic field are antiparallel, while propagation is inhibited on the opposite side. Moreover, propagating spin waves are efficiently excited only in a limited frequency range corresponding to wavevectors inversely proportional to the size of the nanocontact. This frequency range obeys the dispersion relation for exchange-dominated spin waves in the far field, as confirmed by micromagnetic simulations of similar devices. The present results have direct consequences for spin wave based applications, such as synchronization, computation, and magnonics.
|
|
| 2. |
- Tacchi, S., et al.
(författare)
-
Brillouin light scattering investigations of films and magnetic tunnel junctions with perpendicular magnetic anisotropy at the CoFeB-MgO interface
- 2021
-
Ingår i: Journal of Physics D-Applied Physics. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 54:13
-
Tidskriftsartikel (refereegranskat)abstract
- Alternating gradient force magnetometry and Brillouin light scattering (BLS) experiments were exploited to investigate the perpendicular magnetic anisotropy (PMA) localized at the CoFeB-MgO interface, both in Ta/CoFeB/MgO heterostructures (bottom samples) and in the inverted ones MgO/CoFeB/Ta (top samples). Thermal treatment was found to induce a marked increase of the PMA with respect to the as grown state. Using linear spin wave theory, an analysis of the spin wave frequencies was performed which allowed to estimate the thickness dependence of the PMA in the single CoFeB film. Magnetic tunnel junctions with the Ta/CoFeB/MgO/CoFeB/Ta structure were also studied by BLS. The analysis of the experimental results, performed via the linear spin wave theory, revealed that there is an antiferromagnetic interlayer exchange coupling between the free and the fixed CoFeB layers which increases after the annealing procedure.
|
|
| 3. |
- Tacchi, S., et al.
(författare)
-
Co/Pd -CoFeB exchange spring magnets with tunable gap of spin wave excitations
- 2014
-
Ingår i: Journal of Physics D-Applied Physics. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 47:49
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 4. |
- Tacchi, S., et al.
(författare)
-
Epitaxial Fe films on ZnSe(001): effect of the substrate surface reconstruction on the magnetic anisotropy
- 2012
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:23, s. 236006-
-
Tidskriftsartikel (refereegranskat)abstract
- It is well known that Fe films deposited on a c(2 x 2)-reconstructed ZnSe(001) surface show a strong in-plane uniaxial magnetic anisotropy. Here, the effect of the substrate reconstruction on the magnetic anisotropy of Fe has been studied by in situ Brillouin light scattering. We found that the in-plane uniaxial anisotropy is strongly reduced for Fe films grown on a (1 x 1)-unreconstructed ZnSe substrate while the in-plane biaxial one is nearly unaffected by the substrate reconstruction. Calculations of magnetic anisotropy energies within the framework of ab initio density functional theory reveal that the strong suppression of anisotropy at the (1 x 1) interface occurs due to complex atomic relaxations as well as the competing effects originating from magnetocrystalline anisotropy and dipole-dipole interactions. For both sharp and intermixed c(2 x 2) interfaces, the magnetic anisotropy is enhanced compared to the (1 x 1) case due to the further lowering of symmetry. The theoretical results are in agreement with the experimental findings.
|
|
| 5. |
- Tacchi, S., et al.
(författare)
-
Interfacial Dzyaloshinskii-Moriya Interaction in Pt/CoFeB Films : Effect of the Heavy-Metal Thickness
- 2017
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 118:14
-
Tidskriftsartikel (refereegranskat)abstract
- We report the observation of a Pt layer thickness dependence on the induced interfacial DzyaloshinskiiMoriya interaction in ultrathin Pt(d(Pt))/CoFeB films. Taking advantage of the large spin-orbit coupling of the heavy metal, the interfacial Dzyaloshinskii-Moriya interaction is quantified by Brillouin light scattering measurements of the frequency nonreciprocity of spin waves in the ferromagnet. The magnitude of the induced Dzyaloshinskii-Moriya coupling is found to saturate to a value of 0.45 mJ/m(2) for Pt thicknesses larger than similar to 2 nm. The experimental results are explained by analytical calculations based on the three-site indirect exchange mechanism that predicts a Dzyaloshinskii-Moriya interaction at the interface between a ferromagnetic thin layer and a heavy metal. Our findings open up a way to control and optimize chiral effects in ferromagnetic thin films through the thickness of the heavy-metal layer.
|
|
| 6. |
- Tacchi, S., et al.
(författare)
-
Spin wave excitations in exchange-coupled [Co/Pd]-NiFe films with tunable tilting of the magnetization
- 2013
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:14, s. 144426-
-
Tidskriftsartikel (refereegranskat)abstract
- Brillouin light scattering was applied to measure the evolution of spin waves in exchange-coupled [Co/Pd]-NiFe films with out-of-plane/in-plane magnetic anisotropy. Tunable tilting of the magnetization has important effects on the spin wave frequency gap: a substantial increase is observed with decreasing the soft NiFe thickness, while seemingly insignificant tilting angles cause a strong reduction with respect to a film with only the hard [Co/Pd] component. The spin wave frequency is reproduced also in samples, with increased thickness of the upper Pd layer, where a sudden modification in the tilting at the hard/soft interface is caused by the weakening of interlayer exchange.
|
|
