F. U. Hillebrecht

Magnetic moment of Mn in the ferromagnetic semiconductor (Ga0.98Mn0.02)As

We have studied the quasibinary ferromagnetic semiconductor (Ga0.98Mn0.02)As by magnetic circular dichroism in x-ray absorption. We find a richly structured Mn absorption spectrum typical for localized 3d electrons. An analysis of the magnetization-averaged and dichroism line shapes shows a local Mn moment of 4.6μB, which is close to the Hund’s rule moment for the half-filled 3d shell. The magnitude of the dichroism reveals that only about 1/7 of the Mn atoms participate in the ferromagnetic order. Our experiment does not show a distinction between the ferro- and paramagnetic Mn atoms.

Antiferromagnetic Coupling of a Cr Overlayer to Fe(100)

The magnetic moment of Cr overlayers deposited on Fe(100) was investigated by spin-resolved core level photoemission. Data for the Cr 3p level show that a monolayer of Cr is ferromagnetically ordered with a magnetic moment oriented antiparallel to the Fe moments. The results suggest that at room temperature the moment of a Cr monolayer on Fe is of the order of 0.5 to 1μB per Cr atom.

Magnetic linear dichroism in soft X-ray core level photoemission from iron

Abstract We have observed magnetic linear dichroism in soft x-ray core-level photo-emission from ferromagnets: With linearly polarized light, the Fe 3p lineshape depends strongly on the relative orientation of the light electric field vector E and the magnetization vector M . For s-polarized light and collinear orientation of E and M the core level line shows a single peak. With E ⊥ M a double-peaked line is observed. We attribute this change to the MLD effect as predicted recently 1 .

Magnetic properties of Cr overlayers on Fe (invited)

The magnetic properties of Cr overlayers deposited on Fe(100) were investigated by spin‐resolved photoemission. Valence band spectra show a reduction of the overall polarization after deposition of Cr. Data of the Cr 3p core level show for Cr coverages up to about 2 monolayers a polarization opposite to that of the Fe 3p core level. Both findings are evidence for an orientation of the Cr moments antiparallel to the Fe moments. The core level as well as the valence band results are consistent with an average moment of about 1 μB per Cr atom, which is significantly smaller than calculated for a monolayer of Cr on Fe.

High-efficiency spin polarimetry by very-low-energy electron scattering from Fe(100) for spin-resolved photoemission

We describe concept, design, and performance of a novel spin polarimeter based on spin-dependent specular reflection of electrons from a Fe(100) surface. The Fe surface is prepared as an ultrathin film on Ag(100). By tuning the energy of the electrons to a critical point in the Fe band structure, a large spin asymmetry combined with a large scattering efficiency is achieved. The polarimeter yields a figure of merit up to 10−2 for the best Fe(100) surfaces.We describe concept, design, and performance of a novel spin polarimeter based on spin-dependent specular reflection of electrons from a Fe(100) surface. The Fe surface is prepared as an ultrathin film on Ag(100). By tuning the energy of the electrons to a critical point in the Fe band structure, a large spin asymmetry combined with a large scattering efficiency is achieved. The polarimeter yields a figure of merit up to 10−2 for the best Fe(100) surfaces.

Spin-polarized electron spectroscopy as a combined chemical and magnetic probe

Abstract Photoelectron spectra of inner core states of magnetic material show polarization features determined by the magnetic properties of the valence electrons. This offers a new possibilty of using electron spectroscopy as a magnetic probe. The low intensity of these photoemission lines led us to use very-low-energy-electron-scattering from Fe as spinpolarimeter with an efficiency about 20 times higher than previously used spin detection techniques. First experiments on the Fe 3p and 3s core levels confirm exchange split lines. For thin Cr overlayers on Fe(001) we find the polarization of the Cr 3p level for Cr coverages up to two monolayers to be opposite to that of the Fe 3p core level. Effects of the film thickness on the spin-resolved core level spectra are discussed.

Observation of in plane magnetization reversal using polarization dependent magneto-optic Kerr effect

We present an experimental setup for in plane two axis magnetometry using the polarization dependent magneto–optic Kerr effect (MOKE). A conventional setup to measure longitudinal MOKE with crossed polarizers is extended by a Faraday cell to compensate for the rotation of the polarization vector caused by a magnetized sample. The shape of the hysteresis loops measured on thin FeNi alloy films depends strongly on the angle between the optical axis of the analyzer and the plane of incidence. We derive expressions for the compensation angle which allow for extraction of vectorial magnetic information from loops detected with oblique polarization. For a small deviation from pure s or p polarization the transverse magnetization is found to be proportional to the difference between the loop obtained with oblique polarization and the one obtained with pure s or p polarization. Thus the complete in plane reversal process split up into longitudinal and transverse components can be observed.

Linear magnetic dichroism in photoemission

Results for the linear magnetic dichroism of Fe 2p spin-resolved photoemission with high energy resolution are reported. The results are qualitatively similar to those for the 3p level, with the advantage that the fine structure split sublevels (j = 1/2 and j = 3/2) are well separated, facilitating comparison with theoretical models. The finite dichroism in the energy region between the two photoemission peaks is not caused by secondaries, but appears to be a nontrivial effect. The 3p dichroism depends on photon energy: it is maximum at 140 eV, and vanishes around 300 eV photon energy.

Magnetic linear dichroism in angle-resolved valence band photoemission from Fe(001)

Abstract We report the observation of magnetic linear dichroism in angle resolved valence band photoemission from Fe(001), manifesting itself in a change of the spectrum upon reversal of the magnetization direction.

Imaging of magnetic domains by photoemission microscopy

Abstract Imaging of ferromagnetic domains by photoemission microscopy based on magnetic dichroism in the total yield is illustrated by various examples. By using different light polarizations, different components of the magnetization near to the surface can be revealed without movement of the sample. Examples include bulk crystals, ferromagnetic alloys, ultrathin films and submonolayer adsorbates. First results of a time-resolved study under an external magnetic field are presented.