Transverse Kerr Effect Measurements Research Articles

The competition between magnetocrystalline and shape anisotropy on the magnetic and magneto-transport properties of crystallographically aligned CuCr2Se4 thin films

Crystallographically aligned nanocrystalline films of the ferromagnetic spinel CuCr2Se4 were successfully synthesized and their structure and alignment were confirmed by X-ray diffraction and high-resolution transmission electron microscopy. The average size of the crystallites is about 200–250nm, and their (111) crystal planes are parallel to the film plane. A good match of the film’s electronic structure to that of bulk CuCr2Se4 is confirmed by transverse Kerr effect measurements. Four easy 〈111〉 axes are present in the films. One of these axes is oriented perpendicular and three others are oriented at an angle of 19.5° relative to the film plane. The magnetic properties of the films are determined by a competition between the out-of-plane magnetocrystalline anisotropy and the in-plane shape anisotropy. Magnetic measurements show that the dominating type of anisotropy switches from shape to magnetocrystalline anisotropy near 160K, which leads to a switch of the effective easy axis from inside the film plane at room temperature to perpendicular to the film plane as the temperature decreases. At last, a moderately large, negative value of the low-temperature magnetoresistance was observed for the first time in CuCr2Se4 films.

Optical and magneto-optical properties of ferromagneticLa1 − xBaxMnO3 single crystals

The optical and magneto-optical properties of ferromagneticLa1 − xBaxMnO3 singlecrystals with x = 0.15, 0.20 and 0.25 are studied. The components of the permittivity tensor are obtained byspectral ellipsometry techniques and transverse Kerr effect measurements. The Kerr effectspectra depend substantially on the Ba content. The plasma frequency is estimated. In theparamagnetic semiconductor state, the small polarons contribute to conductivity inLa0.85Ba0.15MnO3, inLa0.75Ba0.25MnO3 no evidence for polarons is found even in the semiconductor state. ForLa0.85Ba0.15MnO3 (TC = 214 K), the metallic phase is estimated to occupy less than 1% of the total volume atT = 190 K. It is shownthat in La0.75Ba0.25MnO3, the energy gap vanishes and the metal–semiconductor transition occurs somewhat belowTC ratherthan at T = TC.

Structural and magnetic properties ofCoxSi1−x thin films and multilayers

The structural and magnetic properties of thin films and multilayers based onCoxSi1−x magnetic layers and Si spacers have been studied by surface x-ray diffraction,Auger electron spectroscopy and magneto-optical transverse Kerr effectmeasurements. Surface x-ray diffraction has been used to follow the evolution of theCo lattice as Si is incorporated into the network for the low Si content range,1.00≤x≤0.77, and a contraction of the unit cell, around 0.2% out-of-plane and 0.9% in-plane, has beenfound. No fingerprint of structural anisotropy in the grain size, either parallel orperpendicular to the magnetic easy axis, has been detected. Magneto-optical transverseKerr effect hysteresis loops of single films show both an increase of coercive field and arotation of the magnetic anisotropy axis as Si enters the lattice in the polycrystalline range,1.00≤x≤0.85. For the multilayer case, the loops confirm the formation of antiferromagnetic orderingthrough the layers when the composition of the alloy is tuned to be in the amorphousrange. The corresponding AES signals show asymmetric depth profiles, suggestingthe formation of intermediate compounds at the broader Co-on-Si interfaces.

Manipulation of in-plane uniaxial anisotropy in Fe∕MgO(001) films by ion sputtering

Grazing-incidence Ar+ ion sputtering has been used to produce nanoscale ripples on the surface of the Fe∕Mg(001) system. This way, a uniaxial anisotropy with both controllable strength and orientation can be superimposed on top of the cubic anisotropy, resulting in Fe∕MgO(001) films with unusual anisotropy symmetry. By combining longitudinal and transverse Kerr-effect measurements, different switching processes are revealed. Depending on the orientation of the external magnetic field, one-jump, two-jump, and “reverse” two-jump magnetization reversals can be observed. A simple model, which takes into account the relevant anisotropy energies, is developed to explain the experimentally observed switching fields and to evaluate the domain wall pinning energies of the sputtered sample.

Antiferromagnetic coupling in amorphousCoxSi1−x∕Simultilayers

Antiferromagnetic coupling has been observed in amorphous ${\mathrm{Co}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x}∕\mathrm{Si}$ multilayers prepared by co-sputtering on Si substrates. X-ray reflectivity measurements show that the multilayer structure is well defined, with cumulative roughness values around $0.8\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Alternating gradient magnetometry and magneto-optical transverse Kerr effect measurements show that the films have in-plane uniaxial magnetic anisotropy and that the ${\mathrm{Co}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x}$ layers are antiferromagnetically coupled for Si layer thicknesses lower than $8\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The magnetic field required to switch between antiparallel and parallel configurations is as low as $3\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}$. These results are in contrast with those found in reference polycrystalline $\mathrm{Co}∕\mathrm{Si}$ multilayers, which show no evidence of antiferromagnetic coupling.

Structure and magnetism of single-phase epitaxialγ′−Fe4N

Single phase epitaxial pure ${\ensuremath{\gamma}}^{\ensuremath{'}}\ensuremath{-}{\mathrm{Fe}}_{4}\mathrm{N}$ films are grown on MgO (001) by molecular beam epitaxy of iron in the presence of nitrogen obtained from a radio frequency atomic source. The epitaxial, single phase nature of the films is revealed by x-ray diffraction and by the local magnetic environment investigated by M\"ossbauer spectroscopy. The macroscopic magnetic properties of the ${\ensuremath{\gamma}}^{\ensuremath{'}}\ensuremath{-}{\mathrm{Fe}}_{4}\mathrm{N}$ films are studied in detail by means of transverse Kerr effect measurements. The hysteresis loops are consistent with the cubic atomic structure, displaying easy [100] magnetization directions. The films are single domain at remanence, and the reversal is dominated by 180\ifmmode^\circ\else\textdegree\fi{} or 90\ifmmode^\circ\else\textdegree\fi{} domain wall nucleation and propagation, depending on the applied field direction. When 90\ifmmode^\circ\else\textdegree\fi{} domain walls are responsible for the magnetization reversal, this proceeds in two stages, and the measured coercive fields vary accordingly. Magnetic domain observations reveal the two distinct reversal ---driven by 180\ifmmode^\circ\else\textdegree\fi{} or 90\ifmmode^\circ\else\textdegree\fi{} domain walls--- modes displaying large domains, of the order of mm. From magnetometer techniques, the saturation magnetization, ${\ensuremath{\mu}}_{0}{\mathrm{M}}_{s},$ is measured to be 1.8 T. A magneto-optical torque technique is used to obtain a value of the anisotropy constant of $2.9\ifmmode\times\else\texttimes\fi{}{10}^{4}{\mathrm{J}/\mathrm{m}}^{3}.$

Optical and magneto-optical anomalies for iron on a structured substrate

Measurements of the reflectivity and the transverse Kerr effect for sputtered iron films on flat and structured substrates reveal, for the first time, anomalies in both the optical and magneto-optical behaviour of the structured samples. The presence of anomalies in the transverse Kerr effect measurements, for various orders of diffraction, is much clearer than in those of reflectivity. The results are discussed in terms of the anticipated Rayleigh condition for optical anomalies and the condition for the generation of surface plasmons in iron.

Pulsed laser deposition of Fe thin films in UHV

Pulsed laser deposition has been used to grow oriented iron thin films in ultra high vacuum on a tungsten (110) buffer layer on a substrate of Al 2O 3 (1120). Time-of-flight ion measurements were used to characterise the ablation plume in the fluence range 1.7–6.8 J cm −2, where the ion fraction varied from 0.6 to 0.8 and the average ion energy varied from 120 to 140 eV. The 30 nm iron films were deposited at a fluence of 3.0 J cm −2. In-situ optical reflectivity was used to monitor the film thickness. A substrate temperature of 650°C was found to optimise the crystalline quality of the iron films. Both the tungsten and the iron grow with [110] normal to the substrate. Transverse Kerr effect measurements showed square hysteresis loops with a coercivity of 1.3 kA/m for the iron film grown at 650°C.

Examination of magneto-optic transverse Kerr effect measurements in thin magnetic films exhibiting perpendicular anisotropy

A uniaxial perpendicular magnetic anisotropy is perhaps one of the most important properties exhibited by thin film materials suitable for high-density magneto-optic recording disks. Previous works report studies of this anisotropy in amorphous rare earth-transition metal (RE-TM) alloys using measurements of the polar Kerr magneto-optic effect to provide the basic data. The experimental data so obtained is complementary to that usually provided by torque and VSM magnetometry but are sometimes difficult to analyse and not always unambiguous. The authors describe an examination of the data provided by the transverse Kerr magneto-optic effect in an attempt to provide further useful information concerning the nature of the anisotropy in magneto-optic recording materials.

Magnetic properties of sandwich films based on RCo amorphous alloys (R = rare-earth, Y or Zr)

The magnetic properties of sandwich films, consisting of a soft amorphous CoZr layer placed between two SmCo layers with different coercivities, have been studied. Magnetization reversal in the different layers occurs under different field values and domain walls are then created (or annihilated) at the interface, due to the exchange interactions existing between the Co layers. A peculiar magnetization state has been stabilized in which the magnetization in the two SmCo layers are of opposite directions and a domain wall divides the CoZr central layer into two regions. In this state the magnetization processes are almost completely reversible, in contrast to the irreversible process observed in a single CoZr layer. The magnetization reversal mechanisms in this type of systems have been studied in YCo/GdCo bilayer, using transverse Kerr effect measurements. Nucleation/propagation has been found to occur in all instances.

Vacuum ultraviolet magneto-optical studies of ferromagnetic metals using synchrotron radiation

Magneto-optical spectroscopy of ferromagnetic metals is extended beyond the quartz limit using synchrotron radiation. Real and imaginary parts of the off-diagonal elements of the conductivity tensor are obtained from transverse Kerr effect measurements and optical constants. The magneto-optical spectra for rare-earth metals along with recent vacuum ultraviolet optical data show evidence of 4f excitations, and predict a 4f optical threshold for Gd at 6.1 eV. The magneto-optical spectra of transition metal ferromagnets exhibit primary features resulting from the joint density of states. Structure in the magneto-optical spectra of Ni confirms corresponding peaks observed in recent vacuum ultraviolet optical studies, and assigns the structure to threshold minority spin transitions originating from near the Fermi level. This interpretation agrees with previous conclusions based on infrared magneto-optical studies, and supports the Stoner model description of the magnetic ground state of ferromagnetic Ni.