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We analyze, both experimentally and numerically, the nonlinear regime of the photo-induced coherent magnetization dynamics in cobalt-doped yttrium iron garnet films. Photo-magnetic excitation with femtosecond laser pulses reveals a strongly nonlinear response of the spin subsystem with a significant increase of the effective Gilbert damping. By varying both laser fluence and the external magnetic field, we show that this nonlinearity originates in the anharmonicity of the magnetic energy landscape. We numerically map the parameter workspace for the nonlinear photo-induced spin dynamics below the photo-magnetic switching threshold. Corroborated by numerical simulations of the Landau-Lifshitz-Gilbert equation, our results highlight the key role of the cubic symmetry of the magnetic subsystem in reaching the nonlinear spin precession regime. These findings expand the fundamental understanding of laser-induced nonlinear spin dynamics as well as facilitate the development of applied photo-magnetism.

It has been hypothesized that α-Klotho deficiency might contribute to chronic inflammation in patients with end-stage renal disease (ESRD), especially those on hemodialysis (HD). Serum Klotho levels by some authors are considered a potential predictor of cerebrovascular events. Therefore, we analyzed serum levels of α-Klotho with ELISA and inflammation-related cytokines in HD patients. Sixty-seven HD patients and 19 healthy people were recruited between November 2017 and June 2021. A Cytometric Bead Array (CBA) was used to determine the level of different cytokines: IL-12p70, TNF, IL-10, IL-6, IL-1β, and IL-8. A human Klotho ELISA kit was used to determine the level of α-Klotho in the plasma samples of HD patients. There was no difference in serum levels of α-Klotho between HD patients and healthy people. Patients had increased serum IL-6 and IL-8. Significant positive correlations existed between the concentration of α-Klotho and the serum concentrations of IL-12p70, IL-10, and IL-1β. However, in a multivariable linear regression analysis, only patients’ age was associated independently with α-Klotho level. Serum α-Klotho was not associated with higher mortality risk in HD patients. While these results draw attention to potential relationships between α-Klotho proteins and inflammatory markers in HD patients, our cross-sectional study could not confirm the pathogenic link between α-Klotho, inflammation, and cardiovascular mortality.

The magnetic properties of NiO/Co/Pt as a function of Co layer thickness were investigated by polar magneto-optical Kerr effect (PMOKE) (magnetometry and microscopy) and Brillouin Light Scattering (BLS) spectroscopy. PMOKE measurements revealed strong surface anisotropy (1.8 mJ/m2) favoring perpendicular magnetic anisotropy and asymmetric domain wall propagation explained by anticlockwise chirality. BLS measurements show that this chirality is induced by strong interfacial Dzyaloshinskii–Moriya interaction (+ 2.0 pJ/m). This is one of the highest values reported so far for Co layers surrounded by different layers. The observed chirality is opposite to what has been found in Co/oxide interfaces. These results and data published earlier, indicate that the strength of interfacial Dzyaloshinskii–Moriya interaction increases with the amount of stoichiometric NiO. Therefore, this work shows that NiO is the source of the interfacial Dzyaloshinskii–Moriya interaction.

Recent results showed that the ferrimagnetic compensation point and other characteristic features of Tb/Co ferrimagnetic multilayers can be tailored by He+ ion bombardment. With appropriate choices of the He+ ion dose, we prepared two types of lattices composed of squares with either Tb or Co domination. The magnetization reversal of the first lattice is similar to that seen in ferromagnetic heterostructures consisting of areas with different switching fields. However, in the second lattice, the creation of domains without accompanying domain walls is possible. These domain patterns are particularly stable because they simultaneously lower the demagnetizing energy and the energy associated with the presence of domain walls (exchange and anisotropy). For both lattices, studies of magnetization reversal show that this process takes place by the propagation of the domain walls. If they are not present at the onset, the reversal starts from the nucleation of reversed domains and it is followed by domain wall propagation. The magnetization reversal process does not depend significantly on the relative sign of the effective magnetization in areas separated by domain walls.

Background: Ageing is a complex phenomenon that leads to decreased proliferative activity, loss of function of the cells, and cellular senescence. Senescence of the immune system exacerbates individual’s immune response, both humoral and cellular but increases the frequency of infections. We hypothesized that physiological ageing of adaptive immune system occurs in recipients of allogeneic hematopoietic cells transplant (allo-HCT) at faster rate when compared to their respective donors since the small number of donor cells undergo immense proliferative stress restoring recipients hematopoiesis. We compared molecular characterizations of ageing between recipients and donors of allo-HCT: telomeric length, proinflammatory cytokines concentration, and immunophenotypic changes in main lymphocyte subsets – CD4+, CD8+, CD19+, CD56+.Results: Median telomeric length (TL) of CD8+ lymphocytes was significantly longer in donors compared to recipients (on average 2,1kb and 1,7kb respectively, p = 0,02). Similar trends were observed for CD4+ and CD19+ although the results did not reach statistical significance. We have also found trends in the immunophenotype between recipients and donors in the subpopulations of CD4+ (naïve and effector memory), CD8+ Eomes+ and B-lymphocytes (B1 and B2). When grouped according to the history of infections, there were differences between recipients in the TNF-a and Il-4 concentrations. They were higher in the recipients with lower infection number p=0,05 and p=0,003 respectively. Lower infection risk recipients had also significantly greater percentage of NK cells (22,3%) than high-risk patients (9,3%) p=0,04.Conclusions: Our results support the hypothesis of accelerated ageing of the recipients lymphocytes observed mainly in CD8 subset compared to their respective donors. Quantitative changes in recipients immunophenotype in some lymphocyte subsets resemble physiological ageing-associated changes. No difference in cytokine concentrations suggests that inflammageing does not increase in allo-HCT recipients, however a lower infection numbers in HCT recipients seems to be associated with increased concentration of proinflammatory cytokines and increased percentage of NK cells. The GVHD does not affect the rate of ageing. Therefore, the differences between recipients and donors cells may result from the proliferative stress in the early period after allo-HCT and the difference between hosts and recipients microenvironments, the only other variable that may influence the identical cells originating from donor hematopoiesis.

Supplementary Material 1

We investigated the relationship between α-Klotho and cytokines related to inflammation in HD patients. We analyzed levels of α-Klotho with ELISA and inflammatory cytokines with CBA in the serum of HD patients. There was a significant negative correlation between the concentration of serum α-Klotho and patients’ age and the serum concentration of PTH. No correlation has been found between α-Klotho and Ca or Pi. HD time, creatynine or eGFR. However, there were significant positive correlations between the concentration of α-Klotho and the serum concentration of IL-12p70, IL-10, and IL-1β. Furthermore, the concentration of IL-10 and IL-1β was significantly lower in HD patients with low α-Klotho concentrations compared with HD patients with high α-Klotho. However, in a multivariable linear regression analysis, only patients’ age was associated independently with α-Klotho level. While these results draw our attention to potential relationships between α-Klotho proteins and inflammatory markers in HD patients, our cross-sectional study could not fully explain the pathogenic link between α-Klotho and inflammation in these patients. Therefore, further studies are necessary to clarify these relationships. However, this observation aligns with previous studies that confirm a significant relationship between Klotho concentration and human aging.

Modifications of magnetic anisotropy of 30 keV Ga+ ion irradiated ultrathin Co films sandwiched between Au or Pt buffer and capping layers are investigated as a function of magnetic layer thickness, dCo, and the ion fluence, F. Maps (dCo, F) of saturation fields have been derived from local magnetooptical polar Kerr effect (PMOKE) measurements. The areas with increased remanent magnetization and/or saturation fields, which are directly related to the uniaxial anisotropy, adopt linear shapes for the two branches in the maps. They are very distinct, especially for the Pt/Co/Pt system irradiated at lower and higher fluence. Replacement of Pt with Au in the buffer layer results in minor influence on the magnetization properties of the irradiated trilayers. Au as a capping layer significantly decreases the anisotropy in the branch appearing at lower fluence. In the Au/Pt/Au sandwich, a severe reduction of induced anisotropy is observed in both branches. The proposed phenomenological model describing experimentally investigated magnetic anisotropies enables separation of surface and volume contributions to both branches of enhanced anisotropy.

Focused ion beam (FIB) irradiation was applied to an ultrathin Pt/Co/Pt film to create micrometer-sized, square-shaped regions with perpendicular orientation of magnetization embedded in an in-plane magnetized environment. The FIB parameters like ion fluence and scanning direction are used to control the magnetic properties of the irradiated areas. We have studied the magnetic and magnetooptical properties in the irradiated areas as a function of ion fluence by means of component selective magnetooptical Kerr microscopy that measures separately pure polar and pure longitudinal components of magnetization. Two fluence ranges that induce perpendicular magnetization components were observed. In the higher fluence range, four regions with independently inclined out-of-plane magnetization, depending on FIB fast scan direction, and an unexpected magnetic domain structure were distinguished inside the squares irradiated by FIB.

Interlayer magnetic coupling in an Au/Co/Mo/Co/Au system fabricated by molecular beam epitaxy was studied as a function of the thicknesses of the cobalt and molybdenum spacer layers (denoted as dCo and dMo, respectively). Magnetization processes and magnetic domain structures were investigated using magneto-optical techniques. In the investigated thickness ranges, various magnetization configurations of the Co layers were observed: (A) both perpendicular, (B) perpendicular and in-plane, and (C) both in-plane. The interlayer exchange coupling field HIEC was determined as a function of dMo. With increasing dMo, this coupling changed from antiferromagnetic with a huge coupling field of ≈0.27 T to ferromagnetic and again to antiferromagnetic. A coupling oscillation period of around 1.4 nm was deduced by comparing the experimental data with the Ruderman–Kittel–Kasuya–Yosida model. For configurations (B) and (C), oscillations of the saturation magnetic field HSAT(dMo) perpendicular to the sample plane were found. Simplified and precise analytical expressions for HSAT were proposed by considering HIEC as well as the uniaxial magnetic anisotropy of one and both magnetic layers, respectively. Magnetic ordering was numerically modeled taking into account the dependences of layer anisotropy and exchange coupling on dCo and dMo, respectively. This modeling well described the remanent magnetization map (dCo, dMo) determined using the polar Kerr effect. It is also shown that HIEC(dMo) induced magnetization reorientation from in-plane to out-of-plane or from out-of-plane to in-plane magnetization configurations and canted magnetization of the Co layers.

The X/Co 3nm/Y (where X, Y=Au, Pt) trilayers with as deposited in-plane magnetization alignment were irradiated with 30 keV Ga+ ions in the wide range of ion fluence. The samples were investigated by means of complementary techniques: magneto-optical magnetometry and spectroscopy (in the photon energy range from 1.2 eV to 4.5 eV), magnetic force microscopy, positron annihilation spectroscopy, X-ray diffraction and reflectivity. Difference in miscibility of interface atoms is clearly manifested in various intermixing extent at Co/Pt and Co/Au interfaces and consequently in magnetic properties of the irradiated trilayers. Low irradiation fluence (~1014 ions/cm2) leads to ~1nm interfaces broadening without visible surface etching for all samples, which is related with a distinct drop of magnetic anisotropy. However, the high irradiation fluence (~5·1015 ions/cm2) results in enhanced interface broadening and significant surface etching (~5 nm) partially removing also Co atoms. Tensile strains (up to 0.5%) were developed in the cover layers. The tensile strain, layers intermixing and the creation of Co-Pt(Au) alloys with different composition formed by irradiation are correlated with the increase of magnetic anisotropy. Moreover it was observed that substitution of Au instead of Pt (as a cap or buffer layer) results in substantial increase of perpendicular magnetic anisotropy. Maximal increase of magnetooptical parameters was observed for Pt/Co/Pt layer. Irradiation induced changes of concentration profiles are revealed using magnetooptical spectra, X-ray reflectivity spectra and simulations with use of binary collision approximation.

Magnetic multilayers of (Ir/Co/Pt)6 with interfacial Dzyaloshinskii-Moriya interaction (IDMI) were deposited by magnetron sputtering with Co thickness d=1.8 nm. Exploiting magneto-optical Kerr effect in longitudinal mode microscopy, magnetic force microscopy, and vibrating sample magnetometry, the magnetic field-driven evolution of domain structures and magnetization hysteresis loops have been studied. The existence of weak stripe domains structure was deduced – tens micrometers size domains with in-plane “core” magnetization modulated by hundred of nanometers domains with out-of-plane magnetization. Micromagnetic simulations interpreted such magnetization distribution. Quantitative evaluation of IDMI was carried out using Brillouin light scattering (BLS) spectroscopy as the difference between Stokes and anti-Stokes peak frequencies Δ f. Due to the additive nature of IDMI, the asymmetric combination of Ir and Pt covers led to large values of effective IDMI energy density Deff. It was found that Stokes and anti-Stokes frequencies as well as Δ f, measured as a function of in-plane applied magnetic field, show hysteresis. These results are explained under the consideration of the influence of IDMI on the dynamics of the in-plane magnetized “core” with weak stripe domains.

We show that it is possible to engineer magnetic multidomain configurations without domain walls in a prototypical rare-earth-transition-metal ferrimagnet using keV He^{+} ion bombardment. We additionally show that these patterns display a particularly stable magnetic configuration due to a deep minimum in the energy of the system caused by flux closure and a corresponding reduction of the magnetostatic energy without an increase in energy by exchange and anisotropy terms across the walls. This occurs because light-ion bombardment affects an element's relative contribution to the properties of the ferrimagnet differently. Therefore, it is possible to control the relative contribution from each magnetic subsystem. The selection of material and the use of light-ion bombardment allow us to engineer domain patterns in continuous magnetic films, which open a way to fabricate them in a much smaller scale than currently possible. Our Letter emphasizes that the right criterion to determine the presence or absence of a domain wall is whether there is a rotation of the spin for each sublattice and that changes of the direction of effective magnetization alone do not constitute an appropriate criterion.

The influence of 30 keV Ga+ ion irradiation in the fluence range 0 ÷ 1·1016 ions/cm2 on magnetic properties of Pt(bottom)/Co(3 nm)/Au(top) trilayers grown by the molecular beam epitaxy was studied. Polar magnetooptical Kerr effect magnetometry and Brillouin light scattering spectrometry were used to measure the magnetic anisotropy and the strength of Dzyaloshinskii-Moriya interaction (DMI). The as-deposited sample exhibits in-plane magnetization with an effective anisotropy field of −0.35 ± 0.02 T. Magnetic anisotropy gradually grows as the ion fluence is increased and out-of-plane magnetic anisotropy appears for the fluence above ∼ 3·1015 ions/cm2. The frequency asymmetry in Stokes and anti-Stokes lines Δf, being a measure of DMI strength, was determined from Brillouin light scattering investigations as a function of applied fluence. The effective DMI constant is equal to −0.48 ± 0.05 mJ/m2 in the as-deposited sample. While increasing fluence the parameter Δf: (i) varies non-monotonically (with two maxima) for F smaller than F≈1015 ions/cm2 and (ii) gradually decreases to zero for higher fluences. Our results can be used for the adjustment of DMI interaction in the manufacturing of magnonic nano-devices.

Magnetization processes and magnetic domain structures in Ta/CoFeB/MgO stacks were studied in a series of samples with various CoFeB thicknesses d ranging from 1.24 to 1.60 nm with a step of 0.04 nm, using polar magneto-optical Kerr effect (PMOKE) magnetometry and microscopy. Thickness dependence of the magnetic anisotropy was evaluated and the first and second order anisotropy constants were quantified for each thickness. Accordingly, this dependence was deduced to result in magnetization reorientation from out-of-plane to in-plane through an easy-cone magnetization region (1.39 nm ≤ d ≤ 1.41 nm) as d was increased. PMOKE imaging of the magnetization reversal processes for stacks with out-of-plane easy axis indicated both a significant increase of the density of nucleation centers and a change in domain morphology with increasing d up to the magnetization reorientation thickness. Magnetization reversal dynamics was described by a thermal activation model consistent with a Barkhausen length of about 120 nm. The thinnest films with d = 1.24 and 1.28 nm exhibited straightened narrow stripe domains resulting from magnetic dipolar repulsion. A thorough study of narrow stripe domains was performed via direct and indirect magnetization reversal processes. The application of such structures as spin wave nano-channels could be promising.

Ultrafast photo-magnetism in dielectric garnets reveals a possibility to perform magnetization switching with a single laser pulse. We demonstrate ultrafast photo-magnetic switching in Co-doped iron garnet films at wavelengths relevant to the more-enabled optical L-band window. We studied both photo-induced magnetization precession and switching of magnetization within the near-infrared spectral range using magneto-optical tools. Single laser pulse switching of magnetization around the 1590 nm wavelength has been found in a narrow resonance band using magneto-optical imaging. The high efficiency of this switching, along with a very low-photon absorption in the L-band, makes this phenomenon interesting for both all-optical magnetic recording and data transfer using telecom systems.

Laser-induced irreversible modifications of magnetic properties of molecular beam epitaxy grown X/Co/Y trilayers on Al2O3 substrates were investigated, with combinations of nonmagnetic metals Pt and Au as buffer X and capping layer Y. It is shown that the formation of regions with irreversibly rotated magnetization from in-plane to out-of-plane orientation occurred for Pt/Co/Pt, Pt/Co/Au, and Au/Co/Pt trilayers. In the Au/Co/Au system, the modification of magnetic properties was negligible. Pt/Co/Pt trilayers were also deposited by sputtering on Si/SiO2 substrates. In this case, a significant suppression of laser-induced magnetic modifications was observed and correlated with the lower thermal conductivity of the Si/SiO2 substrate.

The Pt/Co/Pt trilayers irradiated with light pulses of different characteristics and showing the out-of-plane magnetization were investigated by means of the polarized X-ray absorption fine structure technique. The results of studies revealed that the irradiation introduces Co-Pt intermixing and strain in the layers. The Co-Pt alloys composition in the irradiated layer was found to be correlated with the magnetization remanence.

Spatial distribution of magnetization in an ultrathin ferromagnetic Co layer with a lateral gradient of magnetic anisotropy, while approaching spin reorientation transition (SRT) (from perpendicular to in-plane magnetization alignment), has been investigated by means of micromagnetic simulations in the 2-D mode, using OOMMF software. The geometry of the out-of-plane-magnetized domains (parallel stripes, labyrinth, and bubbles) has been found to be dependent on both the initial distribution of magnetization and the direction of the applied magnetic field. A fast decrease in the domain size has been observed while moving toward SRT. In the experiment, Pt/Co/Pt layers with initial in-plane magnetization orientation have been irreversibly modified by femtosecond laser pulses. In the irradiated spot, rings with induced perpendicular magnetic anisotropy have been formed, resulting in an appearance of several local SRTs. Magnetic domain structure in the SRT regions has been visualized using magnetic force microscopy. The experimental observations are qualitatively explained by the results of the micromagnetic simulations.

Amorphous yttrium iron garnet films ranging in thickness from 100 to 600 nm have been produced on single-crystal silicon substrates by sputtering a polycrystalline target with the composition Y3Fe5O12 (yttrium iron garnet) by a mixture of argon and oxygen ions. Before film growth, AlO x or SiO2 buffer layers up to 0.8 μm in thickness were grown on the Si surface. The heterostructures were crystallized by annealing in air at a temperature of 950°C for 30 min. The properties of the films were studied by magneto-optical techniques, using Kerr effect and ferromagnetic resonance measurements. The Gilbert damping parameter reached 2.8 × 10–3 and the effective planar magnetic anisotropy field was independent of the nature of the buffer layer. This suggests that the thin-film heterostructures obtained in this study are potentially attractive for use in spin-wave semiconductor devices.

Context Although allogeneic hematopoietic cells transplantation (allo-HCT) is a well-established, curative option in a variety of hematologic malignancies, its influence on ageing remains poorly understood. Therefore, we launched a comprehensive study, aiming at assessing age-related changes in allo-HCT long-term survivors, compared to their donors. Objective To investigate ageing-associated changes in main lymphocyte subpopulations (CD4, CD8, CD19, CD56), by assessing telomeric shortening and abnormalities in immunophenotype. We hypothesize, that allo-HCT survivors experience, as healthy elderly, telomeric shortening, premature immunosenescence, and inflammaging, caused by clonal expansion required for rebuilding of hematopoiesis. Design Planned duration of the project: August 2019 to August 2020. Material: venous blood. All participants' PBMCs samples undergo telomeric length measurement (qPCR) and immunophenotype assessment. The results will be tested for any correlation with ageing-associated morphological features (such as Klotho protein and calpaincalpastatin system). Patients Population: 20 recipient-donor pairs. To date, we have examined 9 out of 20 scheduled pairs. Allo-HCT recipients had undergone the engraftment due to a variety of hematological malignancies (i.e., AML, ALL, CML, PNH). Median current age of participants — 51.5 years (11 males, 7 females). Enrolled patients are at least 10 years after allo-HCT with intrinsic control of living donors. Main outcome measures The preliminary results suggest an existence of differences in telomeric length between recipients and donors in all lymphocyte subpopulations (2 pairs examined). Results Telomeric length measurement in 2 recipient (R) - donor (D) pairs (average length per chromosome): TCD4+ (R – 11kb, D – 2kb), TCD8+ (R – 8.5kb, D – 6.5kb), CD19+ (R – 9kb, D – 13kb), CD 56+ (R – 4.5kb, D - 9.5kb). Immunophenotype analysis of 9 R-D pairs has shown no statistically significant (p Conclusions The data suggest the differences in telomeric length in all lymphocyte subpopulations tested. We have not found, as yet, any statistically significant differences in immunophenotype. Observed increase in the percentage of NKT-like subpopulation in allo-HTC recipients, similar to that observed in individuals with autoimmune disorders, though interesting, requires further studies. National Science Center, Poland grants: PRELUDIUM (2018/31/N/NZ3/01035), MINIATURA (2019/03/X/NZ3/01848).

Anisotropy of linear and nonlinear magnetooptical (MO) effects in a regular array of Py antidots is studied by means of the MO Kerr effect at the fundamental and second harmonic wavelengths. We have demonstrated that the value of the MO effect, coercivity, and magnetization distribution depend substantially on the azimuthal orientation of the antidots array relatively to the external magnetic field.

We show that it is possible to engineer magnetic multidomain configurations without domain walls in a prototypical rare-earth-transition-metal ferrimagnet using keV He^{+} ion bombardment. We additionally show that these patterns display a particularly stable magnetic configuration due to a deep minimum in the energy of the system caused by flux closure and a corresponding reduction of the magnetostatic energy without an increase in energy by exchange and anisotropy terms across the walls. This occurs because light-ion bombardment affects an element's relative contribution to the properties of the ferrimagnet differently. Therefore, it is possible to control the relative contribution from each magnetic subsystem. The selection of material and the use of light-ion bombardment allow us to engineer domain patterns in continuous magnetic films, which open a way to fabricate them in a much smaller scale than currently possible. Our Letter emphasizes that the right criterion to determine the presence or absence of a domain wall is whether there is a rotation of the spin for each sublattice and that changes of the direction of effective magnetization alone do not constitute an appropriate criterion.

We show that it is possible to engineer magnetic multi-domain configurations without domain walls in a prototypical rare earth/transition metal ferrimagnet using keV He+ ion bombardment. We additionally shown that these patterns display a particularly stable magnetic configuration due to a deep minimum in the free energy of the system which is caused by flux closure and the corresponding reduction of the magnetostatic part of the total free energy. This is possible because light-ion bombardment differently affects an elements relative contribution to the effective properties of the ferrimagnet. The impact of bombardment is stronger for rare earth elements. Therefore, it is possible to influence the relative contributions of the two magnetic subsystems in a controlled manner. The selection of material system and the use of light-ion bombardment open a route to engineer domain patterns in continuous magnetic films much smaller than what is currently considered possible.

In the last decade it was demonstrated that the fastest way to write information employs ultrashort laser pulses. Naturally such experiments raise questions about the ultimate limit of repetition rate at which light can switch a medium between stable bit states. Here the authors demonstrate that with femtosecond pulses it is possible to write and rewrite magnetic bits in iron garnet with a frequency of up to 20 GHz, with the maximum repetition rate being defined by the frequency of ferromagnetic resonance in the field of photoinduced magnetic anisotropy. This finding reveals the principles to be employed in achieving magnetic recording at frequencies far beyond today's state of the art.

Modifications of magnetic and magneto-optical properties of Pt/Co(d Co )/Pt upon Ar+ irradiation (with energy 1.2, 5 and 30 keV) and fluence, F at the range from 2 · 1013-2 · 1016 Ar+ cm-2) were studied. Two 'branches' of increased perpendicular magnetic anisotropy (PMA) and enhanced magneto-optical response are found on 2D (d Co , F) diagrams. The difference in F between 'branches' is driven by ion energy. Structural features correlated with magnetic properties have been analysed thoroughly by x-ray diffraction, Rutherford backscattering spectrometry and positron annihilation spectroscopy. Experimental results are in agreement with TRIDYN numerical calculations of irradiation-induced layers intermixing. Our work discusses particularly structural factors related to crystal lattice defects and strain, created and modified by irradiation, co-responsible for the increase in the PMA.

Modifications of magnetic anisotropy of 30 keV Ga + ion irradiated ultrathin Co films sandwiched between Au or Pt buffer and capping layers are investigated as a function of magnetic layer thickness, d Co , and the ion fluence, F. Maps (d Co , F) of saturation fields have been derived from local magnetooptical polar Kerr effect (PMOKE) measurements. The areas with increased remanent magnetization and/or saturation fields, which are directly related to the uniaxial anisotropy, adopt linear shapes for the two branches in the maps. They are very distinct, especially for the Pt/Co/Pt system irradiated at lower and higher fluence. Replacement of Pt with Au in the buffer layer results in minor influence on the magnetization properties of the irradiated trilayers. Au as a capping layer significantly decreases the anisotropy in the branch appearing at lower fluence. In the Au/Pt/Au sandwich, a severe reduction of induced anisotropy is observed in both branches. The proposed phenomenological model describing experimentally investigated magnetic anisotropies enables separation of surface and volume contributions to both branches of enhanced anisotropy.

The X/Co 3 nm/Y (where X, Y = Au, Pt) trilayers with as deposited in-plane magnetization alignment were irradiated with 30 keV Ga+ ions in the wide range of ion fluence. The samples were investigated by means of complementary techniques: magneto-optical magnetometry and spectroscopy (in the photon energy range from 1.2 eV to 4.5 eV), magnetic force microscopy, positron annihilation spectroscopy, x-ray diffraction and reflectivity. Difference in miscibility of interface atoms is clearly manifested in various intermixing extent at Co/Pt and Co/Au interfaces and consequently in magnetic properties of the irradiated trilayers. Low irradiation fluence (∼1014 ions cm−2) leads to ∼1 nm interfaces broadening without visible surface etching for all samples, which is related with a distinct drop of magnetic anisotropy. However, the high irradiation fluence (∼5 × 1015 ions cm−2) results in enhanced interface broadening and significant surface etching (∼5 nm) partially removing also Co atoms. Tensile strains (up to 0.5%) were developed in the cover layers. The tensile strain, layers intermixing and the creation of Co–Pt(Au) alloys with different composition formed by irradiation are correlated with the increase of magnetic anisotropy. Moreover it was observed that substitution of Au instead of Pt (as a cap or buffer layer) results in substantial increase of perpendicular magnetic anisotropy. Maximal increase of magnetooptical parameters was observed for Pt/Co/Pt layer. Irradiation induced changes of concentration profiles are revealed using magnetooptical spectra, x-ray reflectivity spectra and simulations with use of binary collision approximation.

Asymmetric Ir/Co/Pt and Pt/Co/Ir trilayers with a wedged Co layer (Co thickness d = 0 ÷ 3.6 nm) were deposited by magnetron sputtering on naturally oxidized Si substrates with a Ta/Au buffer. Their magnetic properties have been investigated using magneto-optical polar Kerr effect and Brillouin light scattering (BLS) technique in the Damon-Eshbach geometry. The BLS measurements shows a frequency asymmetry between Stokes and anti-Stokes peaks position, exploited to determine interfacial Dzyaloshinskii-Moriya interaction energy density DS. DS was nearly two times larger for the Ir/Co/Pt trilayer than for the Pt/Co/Ir with opposite chirality. The effective uniaxial magnetic anisotropy and Ds depend non-monotonically on d with a maximum at d ≈ 1.2 nm. The asymmetry in linewidth for Stokes and anti-Stokes peaks is observed for both Ir/Co/Pt and Pt/Co/Ir trilayers for d

The azimuthal anisotropy of the linear and nonlinear magnetooptical Kerr effect has been studied for a structure that is an ordered array with 420-nm-diameter pores in a 30-nm-thick permalloy film on a silicon substrate. The azimuthal anisotropy of the magnetooptical Kerr effect and the coercive force, corresponding to 4 m symmetry of a planar nanopore array, has been established experimentally. The measurements are accompanied with the numerical calculation of the anisotropic magnetization distribution in the structure at different orientations of the applied magnetic field.

The influence of temperature on surface magnetic structure has been studied in Co- and Fe-rich magnetic glass covered microwires. The investigations have been performed using magneto-optical Kerr effect technique with a thermo-controlled system. It was found different types of domain structures depending on the temperature and the microwire composition. These types are characterised by the different domain period and the angle of the inclination of domain walls. It was established the direct correlation between surface domain structures and hysteresis loops. The coexistence of domain walls with different value of mobility has been found. It was observed original mechanism of the domain structure transformation: sharp change in the domain structure without movement of the domain walls.

We report experimental studies on ultrafast laser-induced magnetization dynamics on a picosecond time scale in ultrathin Co/garnet heterostructures. We compare polarization-sensitive nonthermal dynamics in garnet triggered via photoinduced anisotropy with the thermal dynamics in 2 nm Co films. The influence of Gilbert damping on frequency of magnetization precession under an external magnetic field in a garnet film is described. Thermal demagnetization with a 0.81 ps characteristic time is in good agreement with a two-temperature model of electron-lattice coupling.

For the first time, the YIG (2 μm) /TiO2 (0.2 μm) /PZT (400 μm) structures, where YIG is a polycrystalline layer of yttrium-iron garnet (Y3Fe5O12), PZT is an epitaxially mismatched ferroelectric ceramics based on lead zirconate titanate (PbZr0.45Ti0.55O3) were synthesized by means of ion-beam sputtering – deposition technique. Scanning electron microscopy combined by focused ion-beam method indicates the presence of high-quality plane-parallel YIG/TiO2 and TiO2/PZT interfaces. They were obtained by preliminary ion-beam planarization of the substrate surface using an anti-diffusion layer of titanium dioxide TiO2. Atomic force microscopy showed that planarization allows to achieve a surface smoothness of 10 nm. FMR spectroscopy revealed that the ferrite garnet layers are characterized by a resonance absorption linewidth of ~100 Oe. The linewidth broadening is due to the presence of defects and YIG layer roughness because of the substrate imperfection. The calculated values of the spin-wave damping parameter are of the order of 10−3. The obtained YIG/TiO2/PZT structures can serve as media for the spin waves propagation.

We have investigated the magnetization in a ferromagnetic/antiferromagnetic Co/NiO bilayer from room temperature (RT) to 200 °C. Using polar magneto-optical Kerr effect (PMOKE) based magnetometry, we observe the temperature-induced spin reorientation transition of the Co layer at 150 °C (from out-of-plane to in-plane state). Zero field cooling (ZFC) down to RT leads to the appearance of a micrometer size domain structure and demagnetization of the sample. The remanence magnetization after the ZFC process strongly depends on the temperature from which the cooling process starts (onset temperature). The domain structure and its evolution under the external out-of-plane magnetic field were studied with magnetic force and PMOKE microscopies.

International audience; 30 keV Ga + irradiation-induced changes of magnetic and magneto-optical properties of sputtered Pt/Co/Pt ultrathin trilayers films have been studied as a function of the ion fluence. Out-of-plane magnetic anisotropy states with enhanced magneto-optical effects were evidenced for specific values of cobalt thickness and irradiation fluence. Results obtained after uniform or quasi-uniform focused ion beam irradiation on either out-of-plane or in-plane magnetized sputtered pristine trilayers are compared. Similar irradiation-induced magnetic changes are evidenced in quasi-uniformly focused ion beam or uniformly irradiated films, grown either by sputtering or molecular beam epitaxy. We discuss on plausible common mechanisms underlying the observed effects.

Magnonic crystals (metamaterials to control magnetism) are attractive for manipulating spin waves in digital logic and storage applications, but in the end one needs to be able to actually produce them---an interesting challenge in nanotechnology. This work shows how interlayer coupling and magnetization strength can be engineered in Co/Mo/Co ultrathin-film structures by ion irradiation. Modifications of magnetic properties are correlated to and explained by structural evolution, as revealed by numerical simulations. The authors propose numerous types of magnonic crystals that can be fabricated according to these insights.

Modifications of the magnetic properties of Co=Mo=Co films activated by irradiation with 30-keV Ar and 17-keV Ne ion beams are investigated and compared with the influence of 35-keV Ga ions. This system is magnetized in the sample plane and exhibits a twofold anisotropy. The interlayer coupling of magnetization in as-deposited structures is parallel except for the Mo spacer thickness range between 0.5 and 1.0 nm, where the magnetization of the Co layers is antiparallel oriented. The coupling changes and gradually reduced strength of the ferromagnetic properties are compared for all ion types and discussed as a function of the Mo spacer thickness and the ion fluence. The structural evolution of the studied films with increasing fluence determined from TRIDYN simulations is discussed in relation to the observed magnetic changes.We also propose various types of magnonic crystals that can be fabricated by exploiting the results presented in this work.

Because of the importance of the surface magnetic properties for the optimal operation of magnetic sensors based on giant magneto-impedance effect (GMI), for the last few years we have studied the surface magnetization reversal and surface domain structure of glass-coated microwires using the magneto-optical Kerr effect (MOKE) technique [1]. Taking into account that the Curie temperature of Co-based microwires lies in the temperature range of approximately 100–450°C (depending on chemical composition), the surface magnetic structure should experience great transformation in a temperature range higher than room temperature. Moreover internal stresses induced by glass coating are the characteristic feature of glass-coated microwires [2]. Obviously the strength of internal stresses depends on temperature. Therefore now we direct our efforts to a new area of the investigation that is very important for the stable operation of magnetic sensors that use microwires as active elements — the influence of changing temperature on the surface magnetic structure.

Few-nanometers-thick Fe3O4(111) films were epitaxially grown on Pt(111) and Ru(0001) single crystal supports by sequential iron deposition and oxidation in an ultra-high vacuum chamber. The growth of well-ordered magnetite films was confirmed by low energy electron diffraction. The films were covered with a protective Au layer and subjected to magnetic and structural studies in ambient conditions. Magnetic hysteresis loops, recorded using magneto-optical Kerr effect apparatus, confirmed magnetic ordering in both films at room temperature. The Kerr measurements indicated in-plane orientation of magnetization, which was supported by the lack of magnetic contrast in magnetic force microscopy images. Atomic force microscopy revealed significant differences in morphology of the films, tentatively attributed to different lattice mismatch with Pt(111) and Ru(0001) single crystal supports.

The study of the magnetic properties of glass-covered amorphous microwires is reported. This study is focused on the influence of a high frequency electric current and of temperature upon the surface magnetic domain structure. Investigations are performed using the magneto-optical Kerr effect technique, and it is found that the high frequency current and heating process have a great and essential influence upon the surface magnetization reversal and surface domain structure. The induced formation and transformation of the surface magnetic structure are key processes that determine the stable operation of giant magneto-impedance devices.

Magnetic and magneto-optical properties of Pt/Co/Au and Pt/Co/Pt trilayers subjected to 30 keV Ga+ion irradiation are compared. In two-dimensional maps of these properties as a function of cobalt thickness and ion fluence, two branches with perpendicular magnetic anisotropy (PMA) for Pt/Co/Pt trilayers are well distinguished. The replacement of the Pt capping layer with Au results in the two branches still being visible but the in-plane anisotropy for the low-fluence branch is suppressed whereas the high-fluence branch displays PMA. The X-ray absorption spectra and X-ray magnetic circular dichroism (XMCD) spectra are discussed and compared with non-irradiated reference samples. The changes of their shapes and peak amplitude, particularly for the high-fluence branch, are related to the modifications of the local environment of Co(Pt) atoms and the etching effects induced by ion irradiation. Additionally, in irradiated trilayers the XMCD measurements at the PtL2,3-edge reveal an increase of the magnetic moment induced in Pt atoms.

We report the results of a magneto-optical Kerr effect (MOKE) study of the formation and transformation of the surface domain structure in a series of Co- and Fe-rich microwires. The microwires, with a metallic nucleus diameter of 100 μm and glass coating thickness of 20 μm, were studied by highly sensitive MOKE microscopy in the longitudinal geometry. A wide variety of types of surface domain structures was found in two types of microwires examined.

Magnetic polarization of Mo atoms in Co96Mo4 alloy film and Co/Mo multilayered structures has been studied by X-ray magnetic circular dichroism. Samples with Mo spacers of two different thicknesses (0.9 nm and 1.8 nm) were investigated. Mo atoms receive a magnetic moment of −0.21μB in the alloy. In the multilayer with the thinner Mo spacer (d Mo = 0.9 nm) the magnetic moment is much smaller (−0.03μB). In both cases the measured induced moment at the Mo site is oriented antiparallel to the moment at the Co atoms. The presence of the induced moment in the Mo spacer coincides with antiferromagnetic coupling between the Co component slabs. In contrast, neither measurable induced moment at the Mo site nor interlayer coupling between the Co layers has been found for the multilayer with the thicker Mo spacer. Possible mechanisms of the coupling associated with the induced moment are discussed in detail.

This chapter presents different effects of spin wave (SW) optics in patterned thin garnet samples. It focuses on the optical effects of SWs in micrometer yttrium iron garnet (YIG) films, investigated experimentally with aid of the Brillouin light scattering (BLS) technique and simulated numerically, and in nanometer films, investigated theoretically with aid of micromagnetic simulations. Recent fabrication of YIG films with nanometer thickness has opened new frontiers for magnetic studies and made new applications possible because of both the discovery of new effects, such as current-spin wave conversion, or the spin-Seebeck effect, and possibilities for high-quality patterning in submicrometer range, enabling research on SWs of short wavelengths. The SW refraction phenomenon induced by demagnetization field inhomogeneity was proposed as an explanation of the phenomenon of total nonreflection effect of SWs on the antidots line. The chapter discusses SW interactions with different geometrical objects and uses rules known from optics which are based on analysis of iso-frequency dispersion relation lines (IFDRLs).

The application of spin waves in communication with information encoded in amplitude and phase could replace or enhance existing microelectronic and microwave devices with significantly decreased energy consumption. Spin waves (SW) are usually transported in a magnetic material shaped to act as a waveguide. However, the implementation of SW transport and switching in plane homogeneous magnetic films and running as a narrow beam with a small divergence angle still present a challenge. We propose a realization of a strong SW switchers based on a patterned yttrium iron garnet (YIG) film that could serve as a magnonic fundamental building block. Our concept relies on the creation of a narrow beam of relatively short-wavelength SW by effect of a total non-reflection, found to be tied to refraction on the decreasing internal magnetic field, near a line of antidots at YIG. Nonreciprocal SW excitation by a microstrip antenna is used for controlling the direction of the signal flow. We demonstrate unique features of the propagation of microwave-excited SW beams, provide insight into their physics and discuss their potential applications in high-frequency devices.

Magnetic amorphous microwires are the perfect objects for both fundamental studies and technological applications.