Magneto-optical Kerr Spectroscopy Research Articles

Anomalous magneto-optical Kerr hysteresis loops in Fe0.25TaS2

We have performed magneto-optical Kerr spectroscopy measurements on intercalated transition-metal dichalcogenide Fe${}_{0.25}$TaS${}_{2}$ in the polar Kerr geometry as a function of temperature, magnetic field, and wavelength. The Kerr angle exhibits pronounced peaks at $\ensuremath{\sim}$775 nm (1.6 eV) and $\ensuremath{\sim}$515 nm (2.4 eV), which we attribute to spin-dependent interband optical transitions arising from states in the vicinity of the Fermi energy. Below the ferromagnetic transition temperature (165 K) we observe a strongly wavelength- and magnetic-field-dependent Kerr signal. At a fixed wavelength, the magnetic-field dependence of the Kerr angle shows a clear hysteresis loop, but its shape sensitively changes with the wavelength. We propose a model that takes into account contributions from domain walls, which allowed us to derive a mathematical expression that successfully fits all the observed hysteresis loops.

Polar and longitudinal magneto-optical spectroscopy of bismuth substituted yttrium iron garnet films grown by pulsed laser deposition

Ferrimagnetic bismuth substituted yttrium iron garnet Bi x Y 3 − x Fe 5O 12 (BiYIG) films with x = 1 and 2 pulsed laser deposited onto (111) Gd 3Ga 5O 12 (GGG) substrates were studied using magneto-optical (MO) Kerr spectroscopy in the photon energy range of 1.8–5 eV at both polar and longitudinal magnetizations. The interference at lower photon energies provided the refined film thicknesses ranging between 70 and 200 nm. The films were grown under compressive strain and displayed saturation magnetizations ( μ 0 M s) lower than that of their bulk counterparts due to the presence of nanograins forming BiYIG layers and/or magnetically dead interface layers. The trends in the MO spectra agree with those deduced from the published permittivity tensor data for BiYIG using a transfer matrix model applied to a film (BiYIG)–substrate (GGG) system. Due to the reduced μ 0 M s the predicted amplitudes are typically higher. The agreement was improved using effective medium approach or by incorporating into the model MO passive interface layers. The information on MO activity at longitudinal magnetization in the garnet layers below 100 nm presents interest for MO imaging and magnetophotonic devices. The results suggest that the MO Kerr spectroscopy combined with MO Kerr magnetometry may represent a valuable, cheap and nondestructive tool for the characterization of magnetic garnet films less than 200 nm thick.

Above-bandgap magneto-optical Kerr effect in ferromagnetic Ga1−xMnxAs

We performed a systematic magneto-optical Kerr spectroscopy study of Ga${}_{1\ensuremath{-}x}$Mn${}_{x}$As with varying Mn densities as a function of temperature, magnetic field, and photon energy. Unlike previous studies, the magnetization easy axis was perpendicular to the sample surface, allowing us to take remanent polar Kerr spectra in the absence of an external magnetic field. The remanent Kerr angle strongly depended on the photon energy, exhibiting a large positive peak at $~1.7$ eV. This peak increased in intensity and blueshifted with Mn doping and further blueshifted with annealing. Using a 30-band $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ model with antiferromagnetic $s,p$-$d$ exchange interaction, we calculated the dielectric tensor of Ga${}_{1\ensuremath{-}x}$Mn${}_{x}$As in the interband transition region, assuming that our samples are in the metallic regime and the impurity band has merged with the valence band. Our modeling successfully reproduces the observed spectra.

Femtosecond demagnetization and hot-hole relaxation in ferromagneticGa1−xMnxAs

We have studied ultrafast photoinduced demagnetization in GaMnAs via two-color time-resolved magneto-optical Kerr spectroscopy. Below band gap midinfrared pump pulses strongly excite the valence band, while near-infrared probe pulses reveal subpicosecond demagnetization that is followed by an ultrafast $(\ensuremath{\sim}1\text{ }\text{ps})$ partial recovery of the Kerr signal. Through comparison with InMnAs, we attribute the signal recovery to an ultrafast energy relaxation of holes. We propose that the dynamical polarization of holes through $p\text{\ensuremath{-}}d$ scattering is the source of the observed probe signal. These results support the physical picture of femtosecond demagnetization proposed earlier for InMnAs, identifying the critical roles of both energy and spin relaxation of hot holes.

Size dependent damping in picosecond dynamics of single nanomagnets

The authors use time-resolved cavity-enhanced magneto-optical Kerr spectroscopy to study the damping of magnetization precession in individual cylindrical nickel nanomagnets. A wide range of shapes (diameters of 5μm–125nm and aspect ratio: 0.03–1.2) is investigated. They observe a pronounced difference in damping between the micro- and nanomagnets. Microscale magnets show large damping at low bias fields, whereas nanomagnets exhibit bias field-independent damping. This behavior is explained by the interaction of in-plane and out-of-plane precession modes in microscale magnets that results in additional dissipative channels. The small and robust damping values on the nanoscale are promising for implementation of controlled precessional switching schemes in nanomagnetic devices.

Photoinduced Dynamics of Sublattice Magnetization in Ferrimagnets: FeCr2S4 and CoCr2S4

The photoinduced dynamics of sublattice magnetization in ferrimagnetic compounds, FeCr 2 S 4 and CoCr 2 S 4 , was investigated by time-resolved magneto-optical Kerr spectroscopy probing element-spe...

Ultrafast Quenching of Ferromagnetism in InMnAs Induced by Intense Laser Irradiation

Time-resolved magneto-optical Kerr spectroscopy of ferromagnetic InMnAs reveals two distinct demagnetization processes--fast (<1 ps) and slow (approximately 100 ps). Both components diminish with increasing temperature and are absent above the Curie temperature. The fast component rapidly grows with pump power and saturates at high fluences (>10 mJ/cm(2)); the saturation value indicates a complete quenching of ferromagnetism on a subpicosecond time scale. We attribute this fast dynamics to spin heating through p-d exchange interaction between photocarriers and Mn ions, while the approximately 100 ps component is interpreted as spin-lattice relaxation.

General Features of Photoinduced Spin Dynamics in Ferromagnetic and Ferrimagnetic Compounds

Ultrafast photoinduced spin dynamics has been investigated by time-resolved magneto-optical Kerr spectroscopy for various ferromagnetic and ferrimagnetic compounds: FeCr2S4, CoCr2S4, CuCr2Se4, CdCr2Se4, La0.6Sr0.4MnO3, and SrRuO3. The temporal demagnetization process, which is observed commonly for all the compounds, essentially consists of two components: One is an instantaneous change which originates perhaps from multiple emissions of magnetic excitations during nonradiative decay of photoexcited carriers, and the other is a delayed response due to thermalization of the spin system. The time constant of the delayed change depends strongly on materials and is scaled with the magnetocrystalline anisotropy, indicating that spin-orbit coupling is a dominant interaction for this process.

Excitonic enhancement of spin relaxation in diluted magnetic semiconductor quantum wells

We performed pump-probe magneto-optical Kerr spectroscopy to explore the role of excitonic effects on the electron and hole spin relaxation in Cd1˛xMnxTe-based quantum well structures. Particularly, important information is obtained from detailed interpretation of the temperature and wavelength dependence of the observed transient magneto-optics in specially engineered structures. In manganese-rich wells the electron spin relaxation is found to be strongly enhanced in the exciton due to the increased mass of the bound electron-hole pair, in agreement with earlier predictions. An even stronger enhancement of the relaxation time is found for the hole spin, which is explained by the additional mixing of heavy-hole and light-hole states in the bound state. In structures where Mn is confined to the barrier region, a different behavior is observed, indicative for a competition of various contributions.

Terahertz frequency Hall measurement by magneto-optical Kerr spectroscopy in InAs

We report on the time-domain terahertz (THz) magneto-optical Kerr spectroscopy in the frequency range from 0.5 to 2.5 THz. The developed technique employs reflection geometry, enabling high-frequency noncontact Hall measurements in opaque samples. We also present a method to reveal the off-diagonal component of the complex dielectric tensor from the measured polarization-dependent THz wave forms. At a static magnetic field of 0.48 T, a large Kerr rotation over 10° originating from magnetoplasma resonance is observed in an n-type undoped InAs wafer at room temperature. This indicates the strong potential of this material for the polarization modulator in the THz regime.

Effect of Cu thickness in Co/Cu multilayers on polar and longitudinal magneto-optical Kerr spectra

Sputtered Co/Cu multilayers were studied by means of magneto-optical (MO) Kerr spectroscopy. Remarkable changes in the MO spectra were observed for the multilayers where antiferromagnetic coupling take place. This may indicate the changes in the electronic properties of Cu layers. The optical nature of this MO behaviour was verified by ellipsometric measurements.

Optical and magneto-optical investigation on electronic structure of ordered ferromagnetic Fe3Pt

The optical and magneto-optical properties of ordered Fe3Pt have been investigated by spectroscopic ellipsometry and magneto-optical Kerr spectroscopy. The diagonal component of the optical conductivity tensor of the compound exhibits a broad absorption peak at about 2 eV, which is shifted by about 0.5 eV to lower energies from the corresponding one in pure bcc Fe. The Kerr angle spectrum of the compound disperses quite similarly in both spectral trend and magnitude to that of pure Fe below 3.5 eV but differently above it. The lower-energy shift of the 2-eV-absorption structure of the compound is interpreted as due to the shift of the minority-spin Fe-d states toward EF through the hybridization with Pt-d states. The Kerr effect of the compound is attributable to a large spin-orbit coupling in Pt as well as the well-hybridized spin-polarized bands.

Interface effects on the magnetization reversal of Tb/Fe multilayers

The magnetization reversal of multilayers {Tb/Fe/Ag}10(S1), {Fe/Tb/Ag}10(S2), and {Fe/Tb}10(S3) is measured at room and low temperatures using polar magneto-optical Kerr (MOKE) spectroscopy and SQUID magnetometry. The Ag blocking layers in S1 and S2 strongly suppress the perpendicular magnetic anisotropy (PMA) induced by the Fe/Tb interfaces, whereby the Fe-on-Tb interfaces give rise to much stronger PMA than the Tb-on-Fe ones. MOKE ellipticity in the near-infrared reveals an uncoupled soft-magnetic contribution in all samples, S1–S3. It is attributed to amorphous iron segregated within the bulk of the α-Fe layers and contributing to about 10% of their volume.

Comparison of a stoichiometric analysis of Fe 3−δO 4 layers by magneto-optical Kerr spectroscopy with Mössbauer results

The stoichiometry of a series of 300 Å thick Fe 3−δO 4 layers grown by means of molecular beam epitaxy on MgO(100) is been investigated both by magneto-optical Kerr spectroscopy and by Mössbauer spectroscopy. The layers consisted of a 200 Å thick Fe 3−δO 4 layer grown with the 57Fe isotope, sandwiched between two 50 Å thick layers grown with natural Fe. was found that δ varied between 0 and 0.33. From the fits of the polar Kerr spectra of the Fe 3−δO 4 layers measured between 1.4 and 4.0 eV we find, within experimental accuracy, a stoichiometry that is identical to that determined by Mössbauer spectroscopy. This confirms that the magneto-optical Kerr spectra can also be used to determine the stoichiomry of thin Fe 3−δO 4 films.

Investigation of the stoichiometry of MBE-grown Fe 3O 4 layers by magneto-optical Kerr spectroscopy

The polar Kerr spectra between 0.7 and 4.0 eV of single-crystalline layers of Fe 3O 4 grownepitaxially on MgAl 2O 4, SrTiO 3 and MgO (100) substrates by meansof oxidic molecular beam epitaxy are compared to the spectrum of a bulk synthetic single crystal of magnetite to asses the stoichiometry of the layers. Model calculations of the magneto-optical spectra of thin layers are used to explain the differences between the spectra of bulk Fe 3O 4and thin layers of Fe 3O 4. The observed differences are attributed to interference effects and oxidation of the surface of the thin layers. The results are compared to magnetisation and Verwey transition data.

Experimental and theoretical study of the magneto-optical properties of multilayers

DC sputtered Co Pt multilayers have been investigated using magneto-optical (MO) Kerr spectroscopy and SPR LMTO calculations of the MO properties of model Co Pt multilayers have been performed. The results obtained show that the strong MO activity in the UV range is due to alloying effects at the sublayer interface.

HCP-FCC Phase Transition in Co-Ni Alloys Studied With Magneto-Optical Kerr Spectroscopy

ABSTRACTWe have studied 100nm thick electron beam evaporated Co1-xNix alloy films in the composition range 0 ≤ x ≥ 1 using magneto-optical spectroscopy and magnetic anisotropy measurements. For films with x ≈ 0.2 we have also investigated the dependence of these quantities on the growth temperature, which was varied in the range 27 ≤ TG ≥ 408°C. Both as function of the Ni content x and the growth temperature TG we observe the anticipated hcp → fcc phase transition, e.g. by monitoring the magneto-crystalline anisotropy constant Ku, 1, which changes continuously from values of ≈ 0.3MJ/m3 for Co rich hcp alloys (0 ≤ x ≥ 0.25) to ≈ -0.05MJ/m3 for Ni rich fcc alloy films, in good agreement with bulk literature data. The new and most striking result, however, is observed in the polar magneto-optical Kerr and ellipticity spectra, which were measured in the photon energy range 0.8 ≤ hv ≥ 5.5eV. Changes by up to about 40% in Kerr rotation for films of constant composition and magnetization are observed when the structure changes from hcp → fcc. This demonstrates the sensitivity of magneto-optical effects to structural changes, making Kerr spectroscopy a useful electronic and physical structure probe.

Magneto Optical Kerr Spectroscopy as a Probe of Chemical Ordering in CoPt

AbstractWe demonstrate that the photon energy dependence of the polar Kerr effect can be used as a sensitive probe of chemical ordering effects in binary intermetallic alloys. We demonstrate this effect in the Co50Pt50 alloy, which is known to have a Ll0 phase (critical temperature ∼825°C). Kerr spectra of the ordered and disordered phases of the Co50Pt50 alloy composition differ drastically from each other and the ordered phase shows an unprecedented, new peak at 2.2eV photon energy. The intensity of this new peak correlates with the degree of chemical ordering and the magnetic anisotropy in these films.

Magneto-Optical Spectroscopy of RE/TM Alloys and TM/CO Multilayers

ABSTRACTThis paper reviews on magneto-optical spectroscopy of alloys, metallic multilayers and interference enhancement structures for magneto-optic (MO) recording. Mainly rare earth transition metal (RE-TM) alloys and Co/transition metal (Co/X) multilayers will be discussed. The read out performance in MO write/read tests is given by tile reflectivity and Kerr rotation strongly depends on the wavelength. While the magneto-optical transitions in the near infrared (IR:≈820nm) are dominated by tile 3d magnetic transition metals Fe and Co, the properties in the ultraviolet (UV: &lt;400nm) can be dominated by either rare earths like Nd or Pr in RE-TM alloys or by exchange polarized Pt or Pd in Co/X multilayers and their respective alloys.In an attempt to correlate the magneto-optic Kerr effect to electronic properties we have systematically investigated alloys and multilayers with x-ray photoemission (XPS) and polar magneto-optical Kerr spectroscopy (0.5–5.3eV range). It is found that electronic 4f levels in Nd or Pr contribute to the Kerr elffct via Γ→, d transitions in the order of 0.3°. Exchange polarized Pd and Pt in Co/X multilayers give rise to a room temperature Kerr rotation in the same order of magnitude via excitations of the 4d and 5d bands, respectively. These effects clearly depend on film compositions and thickness ratios.,