Magnetization manipulation in (Ga,Mn)As by subpicosecond optical excitation
G. V. AstakhovA. V. KimelG. M. SchottA. TsvetkovA. KirilyukD. R. YakovlevG. KarczewskiW. OssauG. SchmidtL. W. MolenkampTh. Rasing
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Abstract:
We demonstrate complete reversal of a full magnetic hysteresis loop of the magnetic semiconductor (Ga,Mn)As by ultrashort optical excitation with a single subpicosecond light pulse, with obvious implications for ultrafast magneto-optical recording. Our approach utilizes the fourfold magnetic anisotropy of (Ga,Mn)As, in combination with the magnetic linear dichroism of the material.Keywords:
Hysteresis
Magnetic semiconductor
Dichroism
CoO/Fe thin films were grown epitaxially onto vicinal Ag(001) and investigated using magneto-optic Kerr effect, x-ray magnetic circular dichroism (XMCD), and x-ray magnetic linear dichroism (XMLD) techniques. We show that the CoO film in the ultrathin regime does not induce a uniaxial magnetic anisotropy but a coercivity enhancement. This result provides a mechanism for the microscopic origin of the rotatable magnetic anisotropy. XMLD measurement further reveals that the underlying mechanism is that the CoO spins are totally rotatable in the ultrathin regime to follow the Fe magnetization.
Vicinal
Linear dichroism
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The strong perpendicular magnetic anisotropy of L10-ordered FePt has been the subject of extensive studies for a long time. However, it is not known which element, Fe or Pt, mainly contributes to the magnetic anisotropy energy. We have investigated the anisotropy of the orbital magnetic moments of Fe 3d and Pt 5d electrons in L10-ordered FePt thin films by Fe and Pt L2,3-edge x-ray magnetic circular dichroism (XMCD) measurements for samples with various degrees of long-range chemical order S. Fe L2,3-edge XMCD showed that the orbital magnetic moment was larger when the magnetic field was applied perpendicular to the film than parallel to it and that the anisotropy of the orbital magnetic moment increased with S. Pt L2,3-edge XMCD also showed that the orbital magnetic moment was smaller when the magnetic field was applied perpendicular to the film than parallel to it, opposite to the Fe L2,3-edge XMCD results although the anisotropy of the orbital magnetic moment increases with S like the Fe edge. These results are qualitatively consistent with the first-principles calculation by Solovyev et al. [Phys. Rev. B 52, 13419 (1995)], which also predicts the dominant contributions of Pt 5d to the magnetic anisotropy energy rather than Fe 3d due to the strong spin-orbit coupling and the small spin splitting of the Pt 5d bands in L10-ordered FePt.
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To clarify whether or not (Ga,Cr)As is an intrinsic diluted magnetic semiconductor, a systematic study of the magnetic circular dichroism (MCD) was carried out for a series of (Ga,Cr)As epilayers grown by the low-temperature molecular-beam epitaxy technique. The present work provides unambiguous evidence for the intrinsic ferromagnetism of the (Ga,Cr)As epilayers with all the necessary properties in accordance with that of a diluted magnetic semiconductor, especially the hysteresis characteristics, which is opened up in the magnetic field dependence of MCD.
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Hysteresis
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Element-specific magnetic hysteresis measurements on heteromagnetic materials have been achieved by using circularly polarized soft-x-rays. Dramatically different Fe and Co hysteresis curves of Fe/Cu/Co trilayers were obtained by recording the magnetic circular dichroism at their respective L3 white lines as a function of applied magnetic field. The data resolve the complicated hysteresis curves, observed by conventional magnetometry, and determine the individual magnetic moments for the Fe and Co layers. The data show a two-step-like hysteresis loop for all three elements, suggesting that the magnetic properties near the interfaces are very different from those away from the interfaces. The Mn layer was found to be ferromagnetic and aligned with the magnetic direction of Fe and Co. These measurements demonstrate a new application of circularly polarized soft-x-rays in the investigation of magnetic systems.
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Angle-dependent x-ray magnetic circular dichroism (XMCD) experiments performed at both the Co and Pt L2,3 edges for a cubic CoPt3 thin film, which exhibits growth-induced chemical anisotropy, are used to determine the element specific magnetic anisotropy. The large decrease of the 3d orbital moment, observed when the spins are forced out the easy axis of magnetization by the applied magnetic field, is a consequence of a strong magnetocrystalline anisotropy (MCA). In addition, a weak but systematic variation of the Pt orbital moment indicates that the 5d atoms could play an important role in the MCA. These results correlate the microscopic XMCD evaluation of the MCA and the local structural anisotropy as observed with x-ray absorption fine structure (XAFS).
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We study the spin and orbital magnetic moments in Ta/Co0.4Fe0.4B0.2/MgO by x-ray magnetic circular dichroism measurements as well as first-principles calculations, in order to clarify the origin of the perpendicular magnetic anisotropy. Both experimental and theoretical results show that orbital magnetic moment of Fe is more anisotropic than that of Co with respect to the magnetization direction. The anisotropy is larger for thinner CoFeB, indicating that Fe atoms at the interface with MgO contribute more than Co to the observed perpendicular magnetic anisotropy.
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Interface perpendicular magnetic anisotropy (PMA) in ultrathin Fe/MgO (001) has been investigated using angular-dependent x-ray magnetic circular dichroism (XMCD). We found that anisotropic orbital magnetic moments deduced from the analysis of XMCD contribute to the large PMA energies, whose values depend on the annealing temperature. The large PMA energies determined from magnetization measurements are related to those estimated from the XMCD and the anisotropic orbital magnetic moments through the spin-orbit interaction. The enhancement of anisotropic orbital magnetic moments can be explained mainly by the hybridization between the Fe 3dz2 and O 2pz states.
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To avoid the occurrence of doped magnetic ion clustering is a challenge in fabrication of diluted magnetic semiconductors (DMSs). In this work, we report the intrinsic ferromagnetic behavior in Co-doped ZnO DMSs induced by Eu codoping. Both structural parameters and magnetic properties demonstrate the existence of an interaction between Co and Eu ions. The observation of multiplet structures for the localized Co 3d states in x-ray absorption and x-ray magnetic circular dichroism characterization evidences that the codoped Eu plays an important role in facilitating the Co substitution of Zn, leading to intrinsic ferromagnetism.
Magnetic semiconductor
Multiplet
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