Effective spin-mixing conductance (g up arrow down arrow eff) is a key importance parameter for developing future spintronic devices. Here, we report on giant enhancement of g up arrow down arrow eff due to the mutual spin pumping effect in Co/Re/Co heterostructures with antiferromagnetic interlayer exchange coupling (IEC) between asymmetric Co layers of different thicknesses through Re spacer layer. Both static and dynamic time-resolved magneto-optical Kerr effect measurements, performed as a function of magnetic field for different thickness of Re (dRe), reveal occurrence of maximum IEC at dRe 0.4 nm. Two hybridized magnetization precession modes with frequencies significantly dependent on IEC strength and magnetic anisotropy of the Co sublayers up to second order are well explained within the macrospin precession model applied. Strong antiferromagnetic bilinear exchange coupling, with J1 parameter up to-1.3 +/- 0.1 mJ/m2 at dRe = 0.4 nm and noncollinear magnetization ordering due to biquadratic coupling with J2 up to 0.18 +/- 0.02 mJ/m2, is determined. The dependence of intrinsic Gilbert damping parameter alpha 0 on dRe, inferred from the field dependence of effective damping parameter, exhibits a very strong enhancement at maximum IEC for the system with mixed magnetic anisotropy of the Co layers. A perfect correlation between the alpha 0 enhancement and the magnitude of IEC in the structure is found. Large effective spin-mixing conductance up to g up arrow down arrow eff 1.6 & times; 103 nm-2, exceeding the values for structures containing uncoupled or single Co layers by more than an order of magnitude, within the spin pumping model is estimated. It is inferred that the strong enhancement of the interfacial spin-mixing conductance is not only due to the high IEC strength, but is also related to the mixed magnetic anisotropy in the antiferromagnetically coupled Co sublayers.

The influence of the Co- and W-layer stacking sequence and the Co-layer thickness d Co on the magnetization precession and damping and magnetic anisotropy is investigated using the all-optical time-resolved magneto- optical Kerr (TRMOKE) effect in asymmetric Pt/W/Co/Pt and Pt/Co/W/Pt heterostructures prepared by molecular beam epitaxy. It is found that the reversing of the stacking sequence of the Co and W layers leads to significant changes in the magnetic-field H dependencies of the magnetization precession frequency f and the effective damping parameter alpha eff for different d Co thicknesses. A quantitative analysis of the f (H) dependencies is carried out within the macrospin precession model, and the effective magnetic anisotropy constants K eff are determined. It is shown that, in addition to the first-order coefficient K 1 , also the second-order K 2 uniaxial anisotropy constant must be taken into account for the Pt/Co/W/Pt stack, while K 2 is insignificant for the reversed Pt/W/Co/Pt stack. From the K eff ( d Co ) dependencies, the interface K s and volume K v anisotropy contributions for all heterostructures are obtained. The value of K s = 1.24 mJ/m2 for the Pt/Co/W/Pt stack is found to be over two times larger as compared to K s = 0.55 mJ/m2 for the Pt/W/Co/Pt one. The interfacial anisotropy induced at the bottom Pt/Co interface in the Pt/Co/W/Pt heterostructure is shown to be significantly larger than that induced at the top Co/Pt interface in the Pt/W/Co/Pt stack. From the effective damping parameter alpha eff ( H ) dependencies, the intrinsic damping alpha 0 is extracted, and the interface-induced damping contributions to alpha 0 within the spin-pumping model are derived. It is found that the effective spin-mixing conductance parameter g up arrow down arrow eff for the Pt/Co/W/Pt structure exceeds 100 nm-2 and is about two times larger than for the Pt/W/Co/Pt one, indicating the dominant Pt/Co-bottom interface contribution to the spin-pumping damping. A correlation between the intrinsic damping alpha 0 and anisotropy constant K 1 for all layered structures studied is found and discussed in terms of the dependence of both quantities on the spin-orbit coupling. It is shown that the magnetic anisotropy parameters determined from the dynamic TRMOKE method agree well with those obtained from complementary measurements performed using the static magneto-optical Kerr effect.

Important aspects of exchange-coupled magnetic layered structures are related to the noncollinear arrangement of sublayer magnetizations which can arise from competition between bilinear (BL) and biquadratic (BQ) interlayer exchange coupling (IEC). In this work, the influence of coexisting BL and BQ IEC of different strengths on magnetization precession in layered systems is investigated both experimentally and theoretically. Laser-induced magnetization precession has been studied in the Fe/Si(dSi) multilayers (MLS) as a function of the amplitude (H) and orientation angle (OH) of external magnetic field using time-resolved magneto-optical Kerr (TRMOKE) effect. Strongly changing characters of precession frequency dependencies omega(H, OH) for Fe sublayer thickness dFe = 3 nm and Si spacer-layer thicknesses (dSi) varying in the range of 0.9-2.4 nm have been observed. Analytical formulas for acoustic and optic mode dispersion relations with coexisting BL and BQ IEC, scaled by J1 and J2 parameters, respectively, for the in-plane effective magnetic anisotropy and arbitrary magnetic field direction were derived, and very good agreement with the experimentally observed frequency dependencies has been obtained. It is shown that BQ coexisting with BL IEC significantly influences on the magnitude and form of dispersion relations. From analytical formula derived, it follows that zero-field optical mode frequency tends to zero as |J1| approaches 2J2. The acoustic and optic mode-crossing effect has been observed and it is found that values of crossing fields and frequency gaps strongly increase as OH angles decrease and depend on relative BL and BQ IEC strengths. The BL IEC is of ferromagnetic type with J1 approximate to 1.6 mJ/m2 for the MLS with dSi = 0.9 nm, and changes to antiferromagnetic one with J1 approximate to -0.9 mJ/m2 for the MLS with dSi = 1.4 nm, while the J2 parameter of BQ IEC decreases from 1.8 to 1.0 mJ/m2. The coupling strengths decrease by one to two orders of magnitude for the sample with dSi = 2.4 nm, but both mode frequencies are still observed and well reproduced by the theory. It is shown that J1 and J2 parameters obtained in the TRMOKE experiment coincide within the estimated error bars with the determined from independent measurements of magnetization processes in the static magneto-optical Kerr effect and interpreted with the use of analytical formulas derived. Numerical solutions of coupled Landau-Lifshitz-Gilbert (LLG) equations for acoustic and optic modes, with inclusion of BL IEC, intrinsic Gilbert damping, and spin-pumping damping terms, and extended to include BQ IEC, were performed and fitted to experimental data. It is shown that determined effective damping coefficients on H and OH dependencies for acoustic and optic modes are very well simulated with the use of LLG equation solutions with Gilbert damping, spin-pumping-damping-related effective spin-mixing conductance, and spin-diffusion length parameters included. The dependencies of the parameters on dSi spacer-layer thickness are discussed and compared with available data for other systems.

We studied the electronic structure of $\beta$-Li$_2$IrO$_3$ insulator within the density-functional theory using the generalized gradient approximation with taking into account strong Coulomb correlations in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. The $\beta$-Li$_2$IrO$_3$ undergoes a pressure-induced structural and magnetic phase transitions at $P_c$ $\sim$4 GPa with symmetry lowering to the monoclinic $C2/c$. The structural phase transition is accompanied by the formation of Ir$_2$ dimers on the zigzag chains, with an Ir-Ir distance of $\sim$2.66~\AA, even shorter than that of metallic Ir. The strong dimerization stabilizes the bonding molecular-orbital state, leads to the collapse of the magnetism and opens the energy gap with a concomitant electronic phase transition from a Mott insulator to band insulator. The resonant inelastic x-ray scattering spectra (RIXS) at the Ir $L_3$ edge were investigated theoretically from first principles. The calculated results are in good agreement with the experimental data. We show that the the drastic reconstruction of the RIXS spectral peak at 0.7 eV associated with the structural $Fddd \rightarrow C2/c$ phase transition at $P_c$ can be related to disappearing of the Coulomb correlations in the high-pressure $C2/c$ phase

The ultrafast magnetization dynamic processes are investigated in a broad timescale range for different laser pump fluences in Niand Mn-rich Heusler alloy film of Ni54.3Mn31.9Sn13.8 composition using time-resolved magneto-optical Kerr effect (TRMOKE) in perpendicular magnetic field geometry. For all fluences used, two distinct types of magnetization dynamics of different timescales: ultrafast up to 2 picoseconds (range I) and slower from 2 ps to hundreds of ps (range II), were observed. The description of the two-step deand remagnetization processes were performed on the basis of microscopic three-temperature model (M3TM) [1] in the frame of extended eM3TM model [2]. In transition from I to II timescale range, the model parameters: electron-lattice coupling gel and demagnetization rate R decreases over two order of magnitude but weakly depend on the fluence. The calculated spin-flip probability asf decreases over one order of magnitude as well. The reasons for demagnetization slowing down effect observed in the Ni-Mn-Sn film in range II are related with lowering of the exchange interaction and Curie temperature proximity [2]. The model parameters gel, R and asf in range I are of the same order as in Ni metal and can be explained through the electron-phonon-mediated spin-flip scattering processes [1].

The ultrafast magnetization dynamic processes are investigated in a wide time scale range for different laser pump fluences in Ni- and Mn-rich Heusler alloy film of Ni54.3Mn31.9Sn13.8 composition using time-resolved magneto-optical Kerr effect (TR-MOKE) in perpendicular magnetic field geometry. For all fluences used, two distinct types of magnetization dynamics of different time scales: ultrafast up to 2 picoseconds and slower from 2 ps to hundreds of ps, were observed. The description of the two-step de- and remagnetization processes was performed in the frame of modified model developed, based on the microscopic three-temperature model (M3TM). The model is based on the assumption that two magnetic sublattices of the Heusler alloy which are weakly exchange coupled due to Curie temperature proximity are responsible for the fast and slow magnetization dynamics. It is demonstrated excellent agreement of the model prediction with experimental data for all the fluences used. It is shown that the values of model parameters determined - demagnetization rates R and spin-flip probabilities a(sf) for one sublattice are of the order reported for the Ni film. It has been found that R parameter value for the second sublattice related to Mn site is over two orders, and a(sf) is up to one order of magnitude lower than in Ni site. It is shown that strong reduction of the spin-flip probability and electron-phonon coupling, and large magnetic moment in the Mn sublattice as compared to the Ni one is the cause of the observed demagnetization slowing down effect in the Heusler alloy studied.

Electronic structure, X-ray absorption, and magnetic circular dichroism (XMCD) spectra in the CoFeMnSi Heusler alloy were studied from first principles. Fully relativistic Dirac linear muffin-tin orbital band structure method was implemented with various exchange–correlation functionals tested. The supercell approach was used to study the influence of intersite disorder, at the levels of 6.25%, 12.5%, and 25% within transition metal sites, on the XMCD spectra at [Formula: see text] edges and spin polarization (SP) at the Fermi level. It is found that most sensitive to Fe–Mn and Co–Fe disorder are XMCD spectra at [Formula: see text] edges of Fe, while the sensitivity decreases from Mn to Co. It is shown that magnetic moments estimated with the use of magneto-optical (MO) sum rules agree with the ab initio calculated ones to within [Formula: see text], [Formula: see text], and [Formula: see text], for Co, Fe, and Mn, respectively. The calculated SP decreases from 99% for ordered CoFeMnSi alloy, to 96% upon 25% Co–Fe disorder, to 83% for Fe–Mn disorder, and to 42% in the case of Co–Mn disorder. The calculated spectra agree well with the available experimental data. The rich XMCD spectral structures are predicted from first principles at Fe, Co, Mn and Si [Formula: see text] edges.

Laser-induced magnetization dynamics was investigated in Co/Pt/Co trilayer, with 1 nm thick Co-sublayers, as a function of Pt-spacer layer thickness (d(Pt)) using time-resolved magneto-optical Kerr effect. The magnetization precession parameters: frequency (f), amplitude (A) and effective damping parameter (alpha(eff)) dependencies on the external magnetic field (H) were determined as a function of d(Pt). Three different regions of Pt layer thickness: 0-1.3 nm, 1.3-2.5 nm, and 2.5-4 nm, denoted as regions I, II, and III, respectively, exhibiting distinctly different magnetic properties, were distinguished. It is found that as d(Pt) increases reorientation of Co-magnetizations from in-plane to perpendicular direction occurs at d(Pt) around 1.2 nm. For d(Pt) > 2.5 nm magnetization reorientation from parallel to the orthogonal directions due to mixed anisotropies in Co-layers appears. It is found that in the whole d(Pt) range single magnetization precession frequency occurs, despite different effective magnetic anisotropies of Co-sublayers. Simulation of the magnetization precession parameters was performed in an effective magnetic layer model. We found that the observed A(H) behavior is well simulated within the model in region I and III. The alpha(eff) (H) correlations with A(H) in different d(Pt) regions are discussed.

Laser-induced magnetization precession is investigated in Ni-Mn-Sn Heulser alloy film using pump-probe all-optical technique. The studies are performed as a function of external magnetic field H applied at various angles theta(H) with respect to the sample normal. Strong dependence of precession parameters, frequency f, amplitude A and effective damping alpha(eff) on H and theta(H) was found. For H > 3 kOe and theta(H) < 25 degrees, two precession modes, identified as Damon-Eshbach (DE) and first-order standing spin wave (PSSW) modes were observed. The values of wave vector k = 0.37 mu m(-1) for DE mode and exchange constant alpha(eff) = 0.22 mu erg cm(-1) for PSSW mode have been determined. The theta(H) increases up to six times as OH decreases from 55 degrees to 5 degrees and exhibits a maximum at around H = 1.8 kOe for each OH. From experimentally obtained exponentially decayed alpha(eff)(H) dependencies, intrinsic damping alpha(0)(theta(H)) is estimated to ti 0. 025. The dependencies of the magnetization precession parameters have been well simulated in the frame of phenomenological approach, based on Landau-Lifshitz-Gilbert equation.

The influence of the amplitude of an external magnetic field (H) and femtosecond laser pulse fluence (F) on ultrafast magnetization dynamics has been investigated in a ferromagnetic Ni54.3Mn31.9Sn13.8 Heusler-alloy film using the time-resolved magneto-optical Kerr effect. A large slowing down of the demagnetization process was observed and characteristic parameters of magnetization precession were determined for a wide range of H and F values. Long demagnetization times of the order of hundreds of picoseconds have been found and explained as a result of the Curie temperature (T-C) proximity in the alloy film studied. Effective magnetic anisotropy field (H-k(eff)) and Gilbert damping parameter dependencies were determined. A significant reduction of the precession frequency versus F of the uniform Kittel mode was found. A strong decrease of H-k(eff) with F was well simulated in the frame of an extended version of the microscopic three-temperature model (eM3TM), and explained by the T-C proximity effect. The estimated low values of the eM3TM model parameters, the demagnetization rate and electron-lattice coupling constant, appeared essential to explain the slowing down effect of demagnetization. Precession amplitude dependencies were explained by a phenomenological approach taking into account H-k(eff) and changes of the equilibrium magnetization angles induced by pump-pulse excitation.

We studied the electronic, magnetic, and optical properties of beta-Li2IrO3 insulator within the density-functional theory using the generalized gradient approximation taking into account strong Coulomb correlations (GGA+U) in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. The x-ray absorption spectra and x-ray magnetic circular dichroism (XMCD) at the Ir L-2(,)3 edges were investigated theoretically from first principles. The calculated results are in good agreement with experimental data. We found that the GGA+U approach with Hubbard U-eff = 1.5 eV well describes the optical spectra and XMCD spectra at the Ir L-2(,)3 edges. We investigated the electronic structure of beta-Li2IrO3 under pressure from first principles. The hyperhoneycomb iridate beta-Li2IrO3 is on the border of the magnetic ordering with relatively weak Coulomb electron-electron correlations. The beta-Li2IrO3 undergoes a pressure-induced structural and magnetic phase transitions at P-c = 4.4 GPa with symmetry lowering to the monoclinic C2/c. The structural phase transition is accompanied by a dimerization of the previously equally long x/y Ir-Ir bonds. We find remarkable nonmagnetic ground states of beta-Li2IrO3 at P-c, with a concomitant electronic phase transition from a Mott insulator to band insulators. We found that J(eff) = 1/2 states are still dominant in the low-energy region in high-pressure monoclinic C2/c structure.

We report on the electronic structure and magnetic properties of hybrid heterostructures of the ferromagnetic double perovskite Sr2CrReO6 (SCRO) and ferroelectric BaTiO3 (BTO) calculated in the GGA approach using the fully relativistic spin-polarized Dirac LMTO method. The electronic band structure and optical properties are studied in the BTO and SCRO oxides as well as in SCRO/BTO heterostructures with different supercells: SCRO/BTO monolayered (1 x 1 x 1), (2 x 2 x 1), and (1 x 1 x 2) heterostructures. We investigated theoretically the magnetization, spin and orbital magnetic moments as well as magnetocrystalline anisotropy energy (MAE) in the SCRO on the BTO substrate as a function of the temperature assuming that the finite temperature can be mimicked by the experimental lattice constants corresponding to this temperature. We found that the spin and orbital magnetic moments are monotonic, almost linear functions of temperature but change abruptly at the points of the BTO structural phase transitions. The magnetization M also possesses "jumps" at the structural phase transitions in agreement with the experiment. However, the theoretically predicted jumps in the total magnetic moment are much smaller than the experimentally measured ones. We found that the Cr/Re disorder increases the jump in the magnetic moment by an order of magnitude compared to the calculated data without disorder. The microscopic origin of such huge effect is discussed. The theoretically calculated temperature dependence of the total magnetic moment with 25% of the Cr/Re disorder is in excellent agreement with the critical amplitude, obtained from the fitting of the experimentally measured magnetization M(T). From the theoretically calculated MAE we found that the easy axis of magnetization for the tetragonal and orthorhombic phases is along the < 001 > direction in agreement with the experiment. However, it changes to the < 11 (1) over bar > direction in the rhombohedral phase. The intersite Cr/Re disorder reduces the MAE for the tetragonal and orthorhombic phases and increases it for the rhombohedral phase. We found that the major contribution to the MAE is due to the orbital magnetic anisotropy at the Re site. We also found that the MAE in the monolayered SCRO/BTO heterostructure is significantly increased in comparison with the MAE in SCRO on BTO substrate. The element-specific x-ray absorption spectra as well as the x-raymagnetic circular dichroism at the Ti, Ba, and Re L-2,L-3 edges in SCRO/BTO heterostructures are investigated theoretically from first principles and compared with available experimental spectra.

The work is devoted to studies of ultrafast magnetization dynamics induced by femtosecond laser pulses in ferromagnetic Ni-Mn-Sn shape memory Heusler alloy. We studied epitaxial thin Ni54.3Mn31.9Sn13.8 film deposited on (001) MgO substrate. Spin precession in an external magnetic field was triggered and detected by the time-resolved magneto-optical Kerr effect (TRMOKE) using pump-probe technique in dual color scheme experiment. Measurements were performed as a function of magnetic field H and pulse power P. The measured TRMOKE signal is composed of oscillatory and background components, both decaying exponentially in a nanosecond time scale. The precession frequency was determined and found to be varying in the range of 1-10 GHz with H up to 3 kOe and decreasing linearly with P. The dependence of Gilbert damping parameter alpha on H was determined and discussed.

We report on the electronic structure and magnetic properties of hybrid heterostructures of the ferromagnetic double perovskite Sr2CrReO6 (SCRO) and ferroelectric BaTiO3 (BTO) calculated in the GGA approach using the fully relativistic spin-polarized Dirac LMTO method. The electronic band structure and optical properties are studied in the BTO and SCRO oxides as well as in SCRO/BTO heterostructures with different supercells: SCRO/BTO monolayered (1 × 1 × 1), (2 × 2 × 1), and (1 × 1 × 2) heterostructures. We investigated theoretically the magnetization, spin and orbital magnetic moments as well as magnetocrystalline anisotropy energy (MAE) in the SCRO on the BTO substrate as a function of the temperature assuming that the finite temperature can be mimicked by the experimental lattice constants corresponding to this temperature. We found that the spin and orbital magnetic moments are monotonic, almost linear functions of temperature but change abruptly at the points of the BTO structural phase transitions. The magnetization M also possesses “jumps” at the structural phase transitions in agreement with the experiment. However, the theoretically predicted jumps in the total magnetic moment are much smaller than the experimentally measured ones. We found that the Cr/Re disorder increases the jump in the magnetic moment by an order of magnitude compared to the calculated data without disorder. The microscopic origin of such huge effect is discussed. The theoretically calculated temperature dependence of the total magnetic moment with 25% of the Cr/Re disorder is in excellent agreement with the critical amplitude, obtained from the fitting of the experimentally measured magnetization M (T ). From the theoretically calculated MAE we found that the easy axis of magnetization for the tetragonal and orthorhombic phases is along the 〈001〉 direction in agreement with the experiment. However, it changes to the 〈111̄〉 direction in the rhombohedral phase. The intersite Cr/Re disorder reduces the MAE for the tetragonal and orthorhombic phases and increases it for the rhombohedral phase. We found that the major contribution to the MAE is due to the orbital magnetic anisotropy at the Re site. We also found that the MAE in the monolayered SCRO/BTO heterostructure is significantly increased in comparison with the MAE in SCRO on BTO substrate. The element-specific x-ray absorption spectra as well as the x-ray magnetic circular dichroism at the Ti, Ba, and Re L2,3 edges in SCRO/BTO heterostructures are investigated theoretically from first principles and compared with available experimental spectra.

We report on the electronic structure of hybrid heterostructure combined the ferromagnetic double perovskite Sr2CrReO6 (SCRO) and ferroelectric BaTiO3 (BTO) calculated in the GGA approach using the fully relativistic spin-polarized Dirac LMTO method. The optical and MO properties as well as the X-ray absorption spectra and Xray magnetic circular dichroism at the Ti, Ba, and Re L-2,L-3 edges and O K edges of the SCRO/BTO heterostructures were investigated theoretically from the first principles. It was shown that the calculations reproduce well available experimental spectra and allow to explain the microscopic origin of the SCRO/BTO heterostructures optical, MO and XMCD spectra.

In this joint experimental and ab initio study, we investigated the influence of chemical composition and martensitic phase transition on the electronic, magnetic, optical and magneto-optical properties of ferromagnetic shape-memory Ni-Mn-Sn alloys. Optical properties and polar magneto-optical Kerr effect (MOKE) spectra for Ni-Mn-Sn alloy film of composition Ni54.3Mn31.9Sn13.8 deposited epitaxially on MgO(0 0 1) substrate were measured over the photon energy range [Formula: see text] eV, and the complete set of optical conductivity tensor elements were determined. To explain the microscopic origin of the optical and magneto-optical spectra, extensive first-principles calculations were made, using the spin-polarized fully relativistic linear-muffin-tin-orbital method. The electronic, magnetic and magneto-optical properties of Ni-Mn-Sn Heusler alloys were investigated for the cubic austenitic and 4O orthorhombic martensitic phases, in stoichiometric and off-stoichiometric compositions. The MOKE properties of Ni-Mn-Sn systems are very sensitive to deviation from stoichiometry. It was shown that the ab initio calculations reproduce experimental spectra well, and help to explain the microscopic origin of Ni-Mn-Sn optical and magneto-optical responses. The interband transitions responsible for the prominent structures in the Ni-Mn-Sn MOKE spectra have been identified-they come from relatively narrow energy intervals at several well-defined vicinities of high-symmetry directions of the Brillouin zone. Significant modification of the MOKE spectra can be considered as a fingerprint of martensitic phase transition in Ni-Mn-Sn alloys.

Magneto-optical (MO) response of the noble metals Cu, Ag, and Au in the joint experimental and ab initio theoretical study is reported. The magneto-optical polar Kerr effect (MOKE) spectra of the noble-metal films were measured with the high sensitivity in the applied magnetic field of 1.5 T over the photon energy range 0.74-5.8 eV. Complete set of the optical conductivity tensor elements was determined precisely from the MOKE and the optical spectra measured at the same energy points. The importance of the off-diagonal intraband Drude-type transitions is demonstrated explicitly for each noble metal and found to be a substantial contribution to the observed spectra. It is shown that the first-principles calculations using the spin-polarized fully relativistic Dirac linear-muffin-tin-orbital method with the inclusion of correlation effects by GGA+U approach reproduce well the experimental spectra and allow to explain the microscopic origin of the noble metals' magneto-optical response in terms of interband transitions. Although the energy band structures of Cu, Ag, and Au are very similar, there are some distinctive differences in bandwidths and the energy positions of the bands (especially in X and L symmetry points), mainly due to different spin-orbit splitting and differences in the spatial extent of 3d, 4d, and 5d valence wave functions of noble metals. It was found that the small differences in the band positions lead to significant differences in the MO properties of three noble metals. Although the spin-orbit interaction in Au is about six times larger than in Cu, and approximately two times larger than in Ag, the absolute value of Kerr rotation in Au is of the same magnitude as in Cu and one order of magnitude smaller as compared to Ag. The sharp Kerr effect spectral peak in Ag is not due to the electronic interband transitions, but rather to the plasma-edge splitting. The band-by-band decomposition of the Cu, Ag, and Au MO spectra is presented and the interband transitions responsible for the prominent structures in the spectra are identified. It has been found that main magneto-optical activity of noble metals in external magnetic field originates from interband transitions at well-defined small-volume regions of Brillouin zone located near the "neck" and "belly" of the Fermi surface.

In this joint experimental and ab initio study, we focused on the influence of the chemical composition and martensite phase transition on the electronic, magnetic, optical, and magneto-optical properties of the ferromagnetic shape-memory Ni-Mn-Ga alloys. The polar magneto-optical Kerr effect (MOKE) spectra for the polycrystalline sample of the Ni-Mn-Ga alloy of ${\mathrm{Ni}}_{60}{\mathrm{Mn}}_{13}{\mathrm{Ga}}_{27}$ composition were measured by means of the polarization modulation method over the photon energy range $0.8\ensuremath{\le}h\ensuremath{\nu}\ensuremath{\le}5.8$ eV in magnetic field up to 1.5 T. The optical properties (refractive index $n$ and extinction coefficient $k)$ were measured directly by spectroscopic ellipsometry using the rotating analyzer method. To complement experiments, extensive first-principles calculations were made with two different first-principles approaches combining the advantages of a multiple scattering Green function method and a spin-polarized fully relativistic linear-muffin-tin-orbital method. The electronic, magnetic, and MO properties of Ni-Mn-Ga Heusler alloys were investigated for the cubic austenitic and modulated 7M-like incommensurate martensitic phases in the stoichiometric and off-stoichiometric compositions. The optical and MOKE properties of Ni-Mn-Ga systems are very sensitive to the deviation from the stoichiometry. It was shown that the ab initio calculations reproduce well experimental spectra and allow us to explain the microscopic origin of the ${\mathrm{Ni}}_{2}\mathrm{MnGa}$ optical and magneto-optical response in terms of interband transitions. The band-by-band decomposition of the ${\mathrm{Ni}}_{2}\mathrm{MnGa}$ MOKE spectra is presented and the interband transitions responsible for the prominent structures in the spectra are identified.

The electronic structure and X-ray magnetic circular dichroism (XMCD) spectra of the Ni2MnGa and Cu doped Ni2MnGa Heusler alloys were investigated theoretically from first principles, using the fully relativistic Dirac linear MT-orbital (LMTO) band structure method. Densities of valence states, orbital and spin magnetic moments are analyzed and discussed. The electronic and magnetic structure of Ni-Mn-Ga Heusler alloys were investigated for the cubic austenitic and modulated 7M-like incommensurate martensitic phases. The X-ray absorption spectra ( XAS) and XMCD at the Mn, Ni, Ga, and Cu L-2,L-3,L- and Mn, Ni, and Ga K edges were investigated theoretically from first principles. The origin of the XMCD spectra in the Ni2MnGa compound is examined. The ab initio calculations reproduce well experimental XAS and XMCD spectra. The XAS at the Mn L-2,L-3 edges remains mostly unchanged through martensitic phase transition. A fingerprint of the martensitic phase transition has been found in the Ni L-2,L-3 XAS spectra. The experimental Ni L-3 XAS has a pronounced shoulder at the L-3 peak at around 853 eV. This peak is nearly suppressed in the martensitic state in comparison with the austenitic phase due to the lifting of the degeneracy in the Ni 3d related unoccupied electronic states. The XMCD of the martensitic phase is increased compared to the XMCD of the austenite phase at the Ni and Mn L-2,L-3 edges. (C) 2016 Elsevier B.V. All rights reserved.