RESUMEN
Ultrafast demagnetization in diverse materials has sparked immense research activities due to its captivating richness and contested underlying mechanisms. Among these, the two most celebrated mechanisms have been the spin-flip scattering (SFS) and spin transport (ST) of optically excited carriers. In this work, we have investigated femtosecond laser-induced ultrafast demagnetization in perpendicular magnetic anisotropy-based synthetic antiferromagnets (p-SAFs) where [Co/Pt]n-1/Co multilayer blocks are separated by Ru or Ir spacers. Our investigation conclusively shows that the ST of optically excited carriers can have a significant contribution to the ultrafast demagnetization in addition to SFS processes. Moreover, we have also achieved an active control over the individual mechanisms by specially designing the SAF samples and altering the external magnetic field and excitation fluence. Our study provides a vital understanding of the underlying mechanism of ultrafast demagnetization in synthetic antiferromagnets, which will be crucial in future research and applications of antiferromagnetic spintronics.
RESUMEN
Antiferromagnets (AFMs) with zero net magnetization are proposed as active elements in future spintronic devices. Depending on the critical film thickness and measurement temperature, bimetallic Mn-based alloys and transition-metal oxide-based AFMs can host various coexisting ordered, disordered, and frustrated AFM phases. Such coexisting phases in the exchange coupled ferromagnetic (FM)/AFM-based heterostructures can result in unusual magnetic and magnetotransport phenomena. Here, we integrate chemically disordered AFM γ-IrMn3 thin films with coexisting AFM phases into complex exchange coupled MgO(001)/γ-Ni3Fe/γ-IrMn3/γ-Ni3Fe/CoO heterostructures and study the structural, magnetic, and magnetotransport properties in various magnetic field cooling states. In particular, we unveil the impact of rotating the relative orientation of the thermally disordered and reversible AFM moments with respect to the irreversible AFM moments on the magnetic and magnetotransport properties of the exchange coupled heterostructures. We further reveal that the persistence of thermally disordered and reversible AFM moments is crucial for achieving highly tunable magnetic properties and multilevel magnetoresistance states. We anticipate that the presented approach and the heterostructure architecture can be utilized in future spintronic devices to manipulate the thermally disordered and reversible AFM moments at the nanoscale.
RESUMEN
Interfaces separating ferromagnetic (FM) layers from non-ferromagnetic layers offer unique properties due to spin-orbit coupling and symmetry breaking, yielding effects such as exchange bias, perpendicular magnetic anisotropy, spin-pumping, spin-transfer torques, and conversion between charge and spin currents and vice versa. These interfacial phenomena play crucial roles in magnetic data storage and transfer applications, which require the formation of FM nanostructures embedded in non-ferromagnetic matrices. Here, we investigate the possibility of creating such nanostructures by ion irradiation. We study the effect of lateral confinement on the ion-irradiation-induced reduction of nonmagnetic metal oxides (e.g., antiferro- or paramagnetic) to form ferromagnetic metals. Our findings are later exploited to form three-dimensional magnetic interfaces between Co, CoO, and Pt by spatial-selective irradiation of CoO/Pt multilayers. We demonstrate that the mechanical displacement of O atoms plays a crucial role in the reduction from insulating, non-ferromagnetic cobalt oxides to metallic cobalt. Metallic cobalt yields both perpendicular magnetic anisotropy in the generated Co/Pt nanostructures and, at low temperatures, exchange bias at vertical interfaces between Co and CoO. If pushed to the limit of ion-irradiation technology, this approach could, in principle, enable the creation of densely packed, atomic-scale ferromagnetic point-contact spin-torque oscillator (STO) networks or conductive channels for current-confined-path-based current perpendicular-to-plane giant magnetoresistance read heads.
RESUMEN
This work demonstrates nanoscale magnetic imaging using bright circularly polarized high-harmonic radiation. We utilize the magneto-optical contrast of worm-like magnetic domains in a Co/Pd multilayer structure, obtaining quantitative amplitude and phase maps by lensless imaging. A diffraction-limited spatial resolution of 49 nm is achieved with iterative phase reconstruction enhanced by a holographic mask. Harnessing the exceptional coherence of high harmonics, this approach will facilitate quantitative, element-specific, and spatially resolved studies of ultrafast magnetization dynamics, advancing both fundamental and applied aspects of nanoscale magnetism.