arXiv subjects

H. A. Dürr

Publications and source records attributed to H. A. Dürr.

22 records · Page 2Linked to original sources

arXiv2010

Femtosecond x-ray absorption spectroscopy of spin and orbital angular momentum in photoexcited Ni films during ultrafast demagnetization

We follow for the first time the evolution of the spin and orbital angular momentum of a thin Ni film during ultrafast demagnetization, by means of x-ray magnetic circular dichroism. Both components decrease with a 130 +/- 40 fs time constant upon excitation with a femtosecond laser pulse. Additional x-ray absorption measurements reveal an increase in the spin-orbit interaction by 6 +/- 2 % during this process. This is the experimental demonstration quantifying the importance of spin-orbit mediated processes during the demagnetization.

cond-mat.mtrl-sci↗

arXiv2009

Dual Behavior of Antiferromagnetic Uncompensated Spins in NiFe/IrMn Exchange Biased Bilayers

We present a comprehensive study of the exchange bias effect in a model system. Through numerical analysis of the exchange bias and coercive fields as a function of the antiferromagnetic layer thickness we deduce the absolute value of the averaged anisotropy constant of the antiferromagnet. We show that the anisotropy of IrMn exhibits a finite size effect as a function of thickness. The interfacial spin disorder involved in the data analysis is further supported by the observation of the dual behavior of the interfacial uncompensated spins. Utilizing soft x-ray resonant magnetic reflectometry we have observed that the antiferromagnetic uncompensated spins are dominantly frozen with nearly no rotating spins due to the chemical intermixing, which correlates to the inferred mechanism for the exchange bias.

cond-mat.mtrl-sci↗

arXiv2009

Training Induced Positive Exchange Bias in NiFe/IrMn Bilayers

Positive exchange bias has been observed in the Ni$_{81}$Fe$_{19}$/Ir$_{20}$Mn$_{80}$ bilayer system via soft x-ray resonant magnetic scattering. After field cooling of the system through the blocking temperature of the antiferromagnet, an initial conventional negative exchange bias is removed after training i. e. successive magnetization reversals, resulting in a positive exchange bias for a temperature range down to 30 K below the blocking temperature (450 K). This new manifestation of magnetic training is discussed in terms of metastable magnetic disorder at the magnetically frustrated interface during magnetization reversal.

cond-mat.mtrl-sci↗

arXiv2009

Valence band and core level photoemission spectros-copy of LaFeAsO$_{1-x}$F$_{x}$

We have investigated the electronic structure of LaFeAsO$_{1-x}$F$_{x}$ (x = 0; 0.1; 0.2) by angle-integrated photoemission spectroscopy and local density approximation (LDA) based band structure calculations. The valence band consists of a low energy peak at E = -0.25 eV and a broad structure around E = -5 eV in qualitative agreement with LDA. From the photon energy dependence of these peaks we conclude that the former derives almost exclusively from Fe 3d states. This constitutes experimental evidence for the strong iron character of the relevant states in a broad window around EF and confirms theoretical predictions.

cond-mat.supr-con↗