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We have carried out an experimental and theoretical study of the magnetoresistance MR(H) in the CPP (current perpendicular to the planes) mode for two types of magnetic multilayers that differ only in the ordering of the magnetic layers: [Co(10 A)/Cu(200 A)/Co(60 A)/Cu(200 A)](N) and [Co(10 A)/Cu(200 A)](N)[Co(60 A)/Cu(200 A)](N). The series resistor model predicts that in the CPP mode MR(H) is independent of the ordering of the layers. Nevertheless, the measured MR(H) curves were found to be completely different for the two cases. Calculations based on a realistic band structure and the Kubo formula show that the results are a consequence of a long mean free path.

Charge transfer at metallo-molecular interfaces may be used to design multifunctional hybrids with an emergent magnetization that may offer an eco-friendly and tunable alternative to conventional magnets and devices. Here, we investigate the origin of the magnetism arising at these interfaces by using different techniques to probe 3d and 5d metal films such as Sc, Mn, Cu, and Pt in contact with fullerenes and rf-sputtered carbon layers. These systems exhibit small anisotropy and coercivity together with a high Curie point. Low-energy muon spin spectroscopy in Cu and Sc-C 60 multilayers show a quick spin depolarization and oscillations attributed to nonuniform local magnetic fields close to the metallo-carbon interface. The hybridization state of the carbon layers plays a crucial role, and we observe an increased magnetization as sp 3 orbitals are annealed into sp 2 −π graphitic states in sputtered carbon/copper multilayers. X-ray magnetic circular dichroism (XMCD) measurements at the carbon K edge of C 60 layers in contact with Sc films show spin polarization in the lowest unoccupied molecular orbital (LUMO) and higher π*-molecular levels, whereas the dichroism in the σ*-resonances is small or nonexistent. These results support the idea of an interaction mediated via charge transfer from the metal and dz-π hybridization. Thin-film carbon-based magnets may allow for the manipulation of spin ordering at metallic surfaces using electrooptical signals, with potential applications in computing, sensors, and other multifunctional magnetic devices. emergent magnetism | molecular spintronics | interfacial magnetism | charge transfer | nanocarbon I nterfaces are critical in quantum physics, and therefore we must explore the potential for designer hybrid materials that profit from promising combinatory effects. In particular, the fine-tuning of spin polarization at metallo-organic interfaces opens a realm of possibilities, from the direct applications in molecular spintronics and thin-film magnetism to biomedical imaging or quantum computing. This interaction at the surface can control the spin polarization in magnetic field sensors, generate magnetization spin-filtering effects in nonmagnetic electrodes, or even give rise to a spontaneous spin ordering in nonmagnetic elements such as diamagnetic copper and paramagnetic manganese (1-11).The impact of carbon-based molecules on adjacent ferromagnets is not limited to spin filtering and electronic transport, but extends to induced changes in the metal anisotropy, magnetization, coercivity, and bias (12-14). Charge transfer and d(metal)-π(carbon) orbital coupling at the interface may change the density of states, spin population, and exchange of metallocarbon interfaces (4,15,16). The interaction between the molecule and the metal depends strongly on the morphology and specific molecular geometry (17, 18). It may lead to a change in the density of states at the Fermi energy DOS(E F ) and/or the exchange-correlation integral (I s ) as described by the Stoner criterion for ferr...

We demonstrate an isolated magnetic interface anisotropy in amorphous CoFeB films on (Al)GaAs(001), similar to that in epitaxial films but without a magnetocrystalline anisotropy term. The direction of the easy axis corresponds to that due to the interfacial interaction proposed for epitaxial films. We show that the anisotropy is determined by the relative orbital component of the atomic magnetic moments. Charge transfer is ruled out as the origin of the interface anisotropy, and it is postulated that the spin-orbit interaction in the semiconductor is crucial in determining the magnetic anisotropy.

Time-resolved ellipsometric measurements were made upon Au, Cu, Ag, Ni, Pd, Ti, Zr, and Hf thin films. Using an elliptically polarized pump beam, the decay of the optically induced polarization of the sample was observed. Characteristic relaxation times are extracted and interpreted in terms of scattering of linear and angular momentum of hot electrons. A systematic variation is observed between different metals that reflects their underlying band structure. DOI: 10.1103/PhysRevB.71.233104 PACS number͑s͒: 78.47.ϩp, 42.65.Ϫk, 78.20.Ls Investigations of ultrafast electron dynamics in metals are required to understand and implement phenomena such as ultrafast demagnetization, 1 ultrafast optical generation of magnons, 2 phonons, 3 and optical birefringence and dichroism. 4 The time scales for the linear and angular momentum dynamics of electrons and holes are of particular importance for transport phenomena, where the carrier energy, direction of motion, and spin polarization play a significant role. 5 The corresponding scattering times are determined by the interactions between electrons, holes, and phonons, and by scattering from defects, and are expected to be of the order of a few femtoseconds. 6 Hence, there is a need for time-resolved ͑TR͒ experiments 1-4,7 that have sufficient time resolution to resolve these processes.The interaction between light and matter can be viewed as the creation of a coherent quantum superposition of initial and final electron states that has an associated polarization. Coherence between states with different wave vector requires an intermediate virtual state and the presence of a coherent phonon. A transition may occur when the coherence of the system is broken either due to the finite width of the optical wave packet or by scattering from the environment. The transition results in the absorption of a photon and the creation of a hot electron-hole pair. Values for the decoherence time have been deduced from electronic spectroscopic techniques and TR two-photon photoemission ͑TR 2PPE͒, although their physical interpretation is not straightforward. 7,8 The polarization may persist for a longer time if the hot electron-hole pair retains some memory of the optically induced momentum after a scattering event.TR optical measurements have been used to study the specular inverse Faraday effect ͑SIFE͒ and specular optical Kerr effect 4,9 ͑SOKE͒ in metals, where it has always been assumed that the characteristic relaxation times are so short that the signal shape corresponds to the cross correlation of the pump and probe intensities. In this paper we show that pump-probe measurements of the incoherent part of the SIFE and SOKE may yield relaxation times for the transient polarization in metals that correspond to the relaxation times for the linear and angular momentum of the excited carriers. A correlation between the character of the TR polarization signal and the electronic structure of different groups of metals is revealed.Measurements 10 were performed with 90 fs ͑full width at hal...