Showing papers by "Andrzej Maziewski published in 2010"

Large ultrafast photoinduced magnetic anisotropy in a cobalt-substituted yttrium iron garnet

Abstract: We demonstrate experimentally that excitation of a Co-substituted ferrimagnetic yttrium iron garnet thin film with linearly polarized 100 fs laser pulses triggers large-angle magnetization precession with an amplitude, phase, and frequency determined by the characteristics of the laser pulse. The precession results from a light-induced anisotropy field with a characteristic lifetime of 20 ps, the direction of which is determined by the polarization of the light. Its strength for a pump intensity of $25\text{ }\text{mJ}/{\text{cm}}^{2}$ is 250 G which is comparable to the intrinsic anisotropy of the sample. By choosing the proper laser-pulse parameters, we were able to excite a precession with an amplitude as large as $20\ifmmode^\circ\else\textdegree\fi{}$ and a precession frequency modified by up to 50%.

Magnetization switching in ferromagnetic microwires

Abstract: Magnetization states of amorphous soft ferromagnetic microwires are studied by experiment and theoretically. It is shown that in low applied axial fields, on increasing the circular magnetic field produced by current, the initial homogeneous circular magnetization distribution evolves in three sequential steps: (i) the appearance of a helical magnetization state, (ii) a jump to the helical state with opposite chirality, and (iii) a gradual rotation of magnetization toward the new circular state. An applied, large-enough axial field stabilizes the axial magnetization states, making these transitions continuous and shifting the magnetic hysteresis loops. The origin of these successive magnetization reorientations and switching is explained in the frameworks of the proposed model.

Domain-wall movement control in Co/Au multilayers by He(+)-ion-bombardment-induced lateral coercivity gradients.

Abstract: Defined perpendicular anisotropy gradients in the Co sublayers of a $[\mathrm{Co}(0.6\text{ }\text{ }\mathrm{nm})/\mathrm{Au}(2\text{ }\text{ }\mathrm{nm}){]}_{3}$ sputter-deposited multilayer have been introduced by light ion bombardment through a wedged Au stopper layer. Within such a layer system, domain walls between up- and down-magnetized areas are controllably movable by an external perpendicular homogeneous magnetic field. This method and layer system is very promising for a controlled magnetic particle transport within the stray fields of the moving domain walls.

Direct observation of giant Barkhausen jumps in magnetic microwires

Abstract: Magnetization reversal induced by a circular magnetic field has been studied using the magneto-optical Kerr effect in magnetic microwires. The visualization of the classical effect of a giant Barkhausen jump is reported in a magnetic microwire. It was directly confirmed that the surface giant Barkhausen jump consists of the nucleation of a single circular domain followed by the long distance quick motion of the solitary circular domain walls.

Magnetic states and magnetization reversal in magnetostatically coupled multilayers with low perpendicular anisotropy

Abstract: Multilayers of (F/NF)N composition, where F means a ferromagnetic layer, NF a nonferromagnetic one, and N the number of repetitions, are studied by simulations and theoretically for different magnetic anisotropy characterized by the quality factor, Q (the ratio of the anisotropy energy to be gained by a magnetization along the easy axis perpendicular to the sample surface and the magnetostatic energy of a uniformly magnetized layer along the surface normal). It is shown that the range of the existence of out-of-plane magnetization states could be extended to Q<1 by proper choice of N and the layers thicknesses. The role of magnetostatic interlayer coupling in the formation of vortexlike and sinusoidal-like distributions of the magnetization is revealed. Different magnetization states are mapped onto a (Q,N)-phase diagram. We demonstrate that a (F/NF)N multilayer is a soft magnetic system in which the domain size could be changed by a few orders of magnitude by small variations of Q, N, and/or the NF space...

Formation of magnetic dots in an ultrathin Co film forced by a patterned buffer

Abstract: The novel method for fabricating magnetic dots reported in this work exploits the dependence of the magnetic anisotropy of an ultrathin Co film on its thickness and on the type of the buffer layer. A patterned buffer prepared as self-assembled Au islands with a lateral size of several hundred nanometres grown on a Mo film surface induces mono-domain dots magnetized perpendicularly to the film plane in the epitaxial Co layer. Polar magneto-optical Kerr magnetometry and magnetic force microscopy have been used to investigate the magnetization reversal of the dots. Nucleation of the reversed magnetic domain followed by the unpinned movement of domain walls is discussed as a possible mechanism responsible for magnetization switching.

Domain Structure in (NiFe/Au/Co/Au) $_{10}$ Multilayers With Perpendicular Anisotropy of Co Layers

Abstract: Results of domain structures observation of individual Ni80Fe20 and Co sublayers in sputter deposited (NiFe/Au/Co/Au)10 multilayers, using an element-sensitive method: the photoemission electron microscopy combined with soft X-ray magnetic circular dichroism, are presented. Also, overall domain structures were studied with magnetic force microscopy. The studies allowed us to reveal submicron stripe domains in the investigated samples and the replication of the stripe domains from the Co layers with perpendicular anisotropy to the NiFe layers with easy-plane anisotropy.

Ellipsometric Selective Sensitivity to Magnetic Nanostructures

Abstract: Magneto-optic (MO) ellipsometry of ferromagnetic materials is extremely sensitive to ultra-thin films, multilayers, and nanostructures. It gives a possibility to measure all components of the magnetization vector in the frame of the magneto-optic vector magnetometry and enable us to separate magnetic contributions from different depths and materials in nanostructures, which is reviewed in this article. The method is based on ellipsometric separation using the selective MO Kerr effect. The figure of merit used to quantify the ellipsometric selectivity to magnetic nano structures is defined on the basis of linear matrix algebra. W e show that the method can be also used to separate MO contributions from areas of the same ferromagnetic materials deposited on different buffer layers. The method is demonstrated using both: (i) modeling of the MO ellipsometry response and (ii) MO measurement of ultra-thin Co islands epitaxially grown on self-organized gold islands on Mo/Al2O3 buffer layer prepared using the molecular beam epitaxy at elevated temperatures. The system is studied using longitudinal (in-plane) and polar (perpendicular) MO Kerr effects.