The origin of the 90 degree magneto-optical Kerr rotation in CeSb

We calculate the linear magneto-optical Kerr rotation for CeSb in the near-infrared spectral range. Using an exact formula for large Kerr rotation angles and a simplified electronic structure of CeSb we find at \hbar \omega = 0.46 eV a Kerr rotation of 90 degree which then for decreasing \omega jumps to -90 degree as recently observed. We identify the general origin of possible 180 degree polarization rotations as resulting from mainly nonmagnetic optical properties, in particular from the ratio of the dominant interband resonance frequency to the plasma frequency. The dependence of the Kerr rotation on moments and magnetization is discussed.Comment: 6 pages, REVTEX, 5 eps figure

Theory for Spin-Polarized Oscillations in Nonlinear Magneto-Optics due to Quantum Well States

Using an electronic tight-binding theory we calculate the nonlinear magneto-optical response from an x-Cu/1Fe/Cu(001) film as a function of frequency and Cu overlayer thickness (x=3 ... 25). We find very strong spin-polarized quantum well oscillations in the nonlinear magneto-optical Kerr effect (NOLIMOKE). These are enhanced by the large density of Fe $d$ states close to the Fermi level acting as intermediate states for frequency doubling. In good agreement with experiment we find two oscillation periods of 6-7 and 11 monolayers the latter being more pronounced.Comment: 12 pages, Revtex, 3 postscript figure

Electronic Theory for the Nonlinear Magneto-Optical Response of Transition-Metals at Surfaces and Interfaces: Dependence of the Kerr-Rotation on Polarization and on the Magnetic Easy Axis

We extend our previous study of the polarization dependence of the nonlinear optical response to the case of magnetic surfaces and buried magnetic interfaces. We calculate for the longitudinal and polar configuration the nonlinear magneto-optical Kerr rotation angle. In particular, we show which tensor elements of the susceptibilities are involved in the enhancement of the Kerr rotation in nonlinear optics for different configurations and we demonstrate by a detailed analysis how the direction of the magnetization and thus the easy axis at surfaces and buried interfaces can be determined from the polarization dependence of the nonlinear magneto-optical response, since the nonlinear Kerr rotation is sensitive to the electromagnetic field components instead of merely the intensities. We also prove from the microscopic treatment of spin-orbit coupling that there is an intrinsic phase difference of 90$^{\circ }$ between tensor elements which are even or odd under magnetization reversal in contrast to linear magneto-optics. Finally, we compare our results with several experiments on Co/Cu films and on Co/Au and Fe/Cr multilayers. We conclude that the nonlinear magneto-optical Kerr-effect determines uniquely the magnetic structure and in particular the magnetic easy axis in films and at multilayer interfaces.Comment: 23 pages Revtex, preprintstyle, 2 uuencoded figure

Nonlinear Magneto-Optical Response of ss- and dd-Wave Superconductors

The nonlinear magneto-optical response of $s$- and $d$-wave superconductors is discussed. We carry out the symmetry analysis of the nonlinear magneto-optical susceptibility in the superconducting state. Due to the surface sensitivity of the nonlinear optical response for systems with bulk inversion symmetry, we perform a group theoretical classification of the superconducting order parameter close to a surface. For the first time, the mixing of singlet and triplet pairing states induced by spin-orbit coupling is systematically taken into account. We show that the interference of singlet and triplet pairing states leads to an observable contribution of the nonlinear magneto-optical Kerr effect. This effect is not only sensitive to the anisotropy of the gap function but also to the symmetry itself. In view of the current discussion of the order parameter symmetry of High-T$_c$ superconductors, results for a tetragonal system with bulk singlet pairing for various pairing symmetries are discussed.Comment: 21 pages (REVTeX) with 8 figures (Postscript

Nonequilibrium Magnetization Dynamics of Nickel

Ultrafast magnetization dynamics of nickel has been studied for different degrees of electronic excitation, using pump-probe second-harmonic generation with 150 fs/800 nm laser pulses of various fluences. Information about the electronic and magnetic response to laser irradiation is obtained from sums and differences of the SHG intensity for opposite magnetization directions. The classical M(T)-curve can be reproduced for delay times larger than the electron thermalization time of about 280 fs, even when electrons and lattice have not reached thermal equilibrium. Further we show that the transient magnetization reaches its minimum approx. 50 fs before electron thermalization is completed.Comment: 8 pages, 5 figures, revte

Magnetocrystalline Anisotropy Energy of Transition Metal Thin Films: A Non-perturbative Theory

The magnetocrystalline anisotropy energy E(anis) of free-standing monolayers and thin films of Fe and Ni is determined using two different semi-empirical schemes. Within a tight-binding calculation for the 3d bands alone, we analyze in detail the relation between bandstructure and E(anis), treating spin-orbit coupling non-pertubatively. We find important contributions to E(anis) due to the lifting of band degeneracies near the Fermi level by SOC. The important role of degeneracies is supported by the calculation of the electron temperature dependence of the magnetocrystalline anisotropy energy, which decreases with the temperature increasing on a scale of several hundred K. In general, E(anis) scales with the square of the SOC constant. Including 4s bands and s-d hybridization, the combined interpolation scheme yields anisotropy energies that quantitatively agree well with experiments for Fe and Ni monolayers on Cu(001). Finally, the anisotropy energy is calculated for systems of up to 14 layers. Even after including s-bands and for multilayers, the importance of degeneracies persists. Considering a fixed fct-Fe structure, we find a reorientation of the magnetization from perpendicular to in-plane at about 4 layers. For Ni, we find the correct in-plane easy-axis for the monolayer. However, since the anisotropy energy remains nearly constant, we do not find the experimentally observed reorientation.Comment: 15 pages, Revtex, 15 postscript figure

Nonlinear Magneto-Optics of Fe Monolayers from first principles: Structural dependence and spin-orbit coupling strength

We calculate the nonlinear magneto-optical response of free-standing fcc (001), (110) and (111) oriented Fe monolayers. The bandstructures are determined from first principles using a full-potential LAPW method with the additional implementation of spin-orbit coupling. The variation of the spin-orbit coupling strength and the nonlinear magneto-optical spectra upon layer orientation are investigated. We find characteristic differences which indicate an enhanced sensitivity of nonlinear magneto-optics to surface orientation and variation of the in-plane lattice constants. In particular the crossover from onedimensional stripe structures to twodimensional films of (111) layers exhibits a clean signature in the nonlinear Kerr-spectra and demonstrates the versatility of nonlinear magneto-optics as a tool for in situ thin-film analysis.Comment: 28 pages, RevTeX, psfig, submitted to PR

Ab-initio calculation of Kerr spectra for semi-infinite systems including multiple reflections and optical interferences

Based on Luttinger's formulation the complex optical conductivity tensor is calculated within the framework of the spin-polarized relativistic screened Korringa-Kohn-Rostoker method for layered systems by means of a contour integration technique. For polar geometry and normal incidence ab-initio Kerr spectra of multilayer systems are then obtained by including via a 2x2 matrix technique all multiple reflections between layers and optical interferences in the layers. Applications to Co|Pt5 and Pt3|Co|Pt5 on the top of a semi-infinite fcc-Pt(111) bulk substrate show good qualitative agreement with the experimental spectra, but differ from those obtained by applying the commonly used two-media approach.Comment: 32 pages (LaTeX), 5 figures (Encapsulated PostScript), submitted to Phys. Rev.

Symmetry Analysis of Second Harmonic Generation at Surfaces of Antiferromagnets

Using group theory we classify the nonlinear magneto-optical response at low-index surfaces of fcc antiferromagnets, such as NiO. Structures consisting of one atomic layer are discussed in detail. We find that optical second harmonic generation is sensitive to surface antiferromagnetism in many cases. We discuss the influence of a second type of magnetic atoms, and also of a possible oxygen sublattice distortion on the output signal. Finally, our symmetry analysis yields the possibility of antiferromagnetic surface domain imaging even in the presence of magnetic unit-cell doubling.Comment: 23 pages, 10 figures incorporated. Accepted to Phys. Rev. B, scheduled for July'9