Z. Kurant

Irreversible modification of magnetic properties of Pt/Co/Pt ultrathin films by femtosecond laser pulses

Annealing ultrathin Pt/Co/Pt films with single femtosecond laser pulses leads to irreversible spin-reorientation transitions and an amplification of the magneto-optical Kerr rotation. The effect was studied as a function of the Co thickness and the pulse fluence, revealing two-dimensional diagrams of magnetic properties. While increasing the fluence, the creation of two branches of the out-of-plane magnetization state was found.

Magnetic ordering in ultrathin cobalt film covered by an overlayer of noble metals

The spatial distribution of magnetic properties studied by polar Kerr-effect-based magnetometry are carried out on an ultrathin cobalt wedge covered with a silver wedge whose slopes are perpendicular to each other and subsequently capped with a gold layer. The coercivity field was studied as a function of both cobalt thickness d and silver thickness h. A few monolayers of Ag were found to have a substantial influence on the coercivity field. A similar strong influence of silver coverage on the magnetic anisotropy field was observed. Domain structure evolution during magnetization reversal is investigated using an optical microscope. With an increase of the magnetic field, a magnetization reversal process occurs: first by domain nucleation and next by a domain wall movement towards the higher coercivity region of the sample. Changes of the fractal dimension of the domain wall as well as nucleation center density are investigated. A rapid increase of these parameters is observed while d increases towards the value of spin reorientation transition, which goes from easy-axis to easy-plane magnetization. Similar strong changes were observed while decreasing d to the lowest thickness available for observation. The problem discussed here, of tuning magnetic properties by silver–gold structure, is important from both a general physics and an application point of view, especially because of the possibilities for magnetic film patterning.

Ion irradiation induced enhancement of out-of-plane magnetic anisotropy in ultrathin Co films

Ga+ or He+ irradiated MBE grown ultrathin films of sapphire/Pt/Co(dCo)/Pt(dPt) were studied using polar Kerr effect in wide ranges of both cobalt dCo and platinum dPt thicknesses as well as ion fluences F. Two branches of increased magnetic anisotropy and enhanced Kerr rotation angle induced by Ga+ or He+ irradiation are clearly visible in two-dimensional (dCo, LogF) diagrams. Only Ga+ irradiation induces two branches of out-of-plane magnetization state.

Magnetic Domains and Anisotropy in Ultrathin Au/Co/Au Wedges Deposited on Mica Substrates

Ultrathin cobalt films and wedges in gold envelope Au/Co(d Co 0) were determined for samples with different thicknesses. Annealing induced in the sample: (i) flattening of the cobalt surface; (ii) a decrease of the coercivity field and magnetic anisotropy caused a decrease of thickness of reorientation from easy axis state to easy plane one; (iii) an increase of the Barkhausen volume which contains many cobalt islands creating the chains. Approaching the reorientation region, the character of the magnetization reversal drastically changes from that with the preference of domain wall propagation into the one connected to the domain wall nucleation.

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

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.

Modification of magnetic properties of Pt/Co/Pt trilayers driven by nanosecond pulses of extreme ultraviolet irradiation

An irreversible rotation of magnetization from in-plane to an out-of-plane direction was induced in Pt/Co/Pt epitaxial trilayers by single and multiple pulses of extreme ultraviolet (EUV) irradiations. The radial dependence of remanence, coercivity and saturation fields across the irradiated spots was studied with the help of magneto-optical techniques for the samples with various Co and Pt buffer layer thicknesses. The sample surface and magnetic ordering were investigated using atomic force and magnetic force microscopies. Based on magnetic and morphological changes, the residual stress after thermoplastic deformation in the spot area is discussed as a reason for the observed transformation.

Magnetic phases in Pt/Co/Pt films induced by single and multiple femtosecond laser pulses

Ultrathin Pt/Co/Pt trilayers with initial in-plane magnetization were irradiated with femtosecond laser pulses. In this way, an irreversible structural modification was introduced, which resulted in the creation of numerous pulse fluence-dependent magnetic phases. This was particularly true with the out-of-plane magnetization state, which exhibited a submicrometer domain structure. This effect was studied in a broad range of pulse fluences up to the point of ablation of the metallic films. In addition to this single-pulse experiment, multiple exposure spots were also investigated, which exhibited an extended area of out-of-plane magnetization phases and a decreased damage threshold. Using a double exposure with partially overlapped spots, a two-dimensional diagram of the magnetic phases as a function of the two energy densities was built, which showed a strong inequality between the first and second incoming pulses.

Near infrared and extreme ultraviolet light pulses induced modifications of ultrathin Co films

We report on comparative study of magnetic properties of Pt/Co/Pt trilayers after irradiation with different light sources. Ultrathin Pt/Co/Pt films were deposited by molecular beam epitaxy technique on sapphire (0001) substrates. Pt buffers were grown at room temperature (RT) and at 750°C (high temperature, HT). The samples were irradiated with a broad range of light energy densities (up to film ablation) using two different single pulse irradiation sources: (i) 40 fs laser with 800 nm wavelength and (ii) 3 ns laser-plasma source of extreme ultraviolet (EUV) with the most intense emission centered at 11 nm. The light pulse-driven irreversible structural and as a consequence, magnetic modifications were investigated using polar magneto-optical Kerr effect-based microscopy and atomic and magnetic force microscopies. The light pulse-induced transitions from the out-of-plane to in-plane magnetization state, and from in-plane to out-of-plane, were observed for both types of samples and irradiation methods. Diagrams of the magnetic states as a function of the Co layer thickness and energy density of the absorbed femtosecond pulses were constructed for the samples with both the RT and HT buffers. The energy density range responsible for the creation of the out-of-plane magnetization was wider for the HT than for RT buffer. This is correlated with the higher (for HT) crystalline quality and much smoother Pt/Co surface deduced from the X-ray diffraction studies. Submicrometer magnetic domains were observed in the irradiated region while approaching the out-of-plane magnetization state. Changes of Pt/Co/Pt structures are discussed for both types of light pulses.We report on comparative study of magnetic properties of Pt/Co/Pt trilayers after irradiation with different light sources. Ultrathin Pt/Co/Pt films were deposited by molecular beam epitaxy technique on sapphire (0001) substrates. Pt buffers were grown at room temperature (RT) and at 750°C (high temperature, HT). The samples were irradiated with a broad range of light energy densities (up to film ablation) using two different single pulse irradiation sources: (i) 40 fs laser with 800 nm wavelength and (ii) 3 ns laser-plasma source of extreme ultraviolet (EUV) with the most intense emission centered at 11 nm. The light pulse-driven irreversible structural and as a consequence, magnetic modifications were investigated using polar magneto-optical Kerr effect-based microscopy and atomic and magnetic force microscopies. The light pulse-induced transitions from the out-of-plane to in-plane magnetization state, and from in-plane to out-of-plane, were observed for both types of samples and irradiation methods. Di...

Tailoring magnetic anisotropy gradients by ion bombardment for domain wall positioning in magnetic multilayers with perpendicular anisotropy

Graded anisotropy magnetic materials possess a coercive field changing laterally with position. A simple fabrication procedure to produce such an anisotropy gradient in a polycrystalline Au/Co layer system without lateral thickness variation and with perpendicular magnetic anisotropy, prototypical for a large variety of thin film systems, is shown. The procedure uses light-ion bombardment without the use of a mask. Magnetization reversal in this polycrystalline layer system takes place by unidirectional movement of a single domain wall only in regions with larger anisotropies and anisotropy gradients. In this anisotropy/anisotropy gradient regime, the domain wall is oriented perpendicular to the coercive field gradient, and it can be positioned along the gradient by an appropriate magnetic field pulse. For smaller anisotropies/anisotropy gradients, the natural anisotropy fluctuations of the polycrystalline layer system induce magnetization reversal dominated by domain nucleation.PACS75.30.Gw; 75.70.Cn; 75.60.Ch

Modifications of the magnetization ordering in Co/Mo/Co layers by Ga+ ion irradiation

Molecular beam epitaxy-grown layered structures Co/Mo/Co exhibit an antiparallel coupling of Co films magnetization in the Mo spacer thickness range between 0.5 nm and 1.0 nm and parallel beyond this range. Magnetic properties are substantially modified by beam irradiation of 35 keV Ga+ ions. With the increase in ion fluence, antiparallel coupling switches to the parallel one. Further increase in fluence results in gradual suppression of ferromagnetic behavior of the system. Experimental results are correlated with numerical simulations of layered structure evolution driven by irradiation.