The exchange bias coupling at ferromagnetic/antiferromagnetic interfaces in epitaxially grown Co/CoO layers can intentionally be increased by a factor of up to 3 if the antiferromagnetic CoO layer is diluted by nonmagnetic defects in its volume part away from the interface. Monte Carlo simulations of a simple model of a ferromagnetic layer on a diluted antiferromagnet show exchange bias and explain qualitatively its dilution and temperature dependence. These investigations reveal that diluting the antiferromagnet leads to the formation of volume domains, which cause and control exchange bias.

We report on the first systematic study of spin transport in bilayer graphene (BLG) as a function of mobility, minimum conductivity, charge density and temperature. The spin relaxation time τ s scales inversely with the mobility µ of BLG samples both at room temperature (RT) and at low temperature (LT). This indicates the importance of D'yakonov -Perel' spin scattering in BLG. Spin relaxation times of up to 2 ns at RT are observed in samples with the lowest mobility. These times are an order of magnitude longer than any values previously reported for single layer graphene (SLG). We discuss the role of intrinsic and extrinsic factors that could lead to the dominance of D'yakonov-Perel' spin scattering in BLG. In comparison to SLG, significant changes in the carrier density dependence of τ s are observed as a function of temperature.

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An overview of one-and two-dimensional quantum spin systems based on transition-metal oxides and halides of current interest is given, such as spinPeierls, spin-dimer, geometrically frustrated and ladder systems. The most significant and outstanding contributions of magnetic light scattering to the understanding of these materials are discussed and compared to results of other spectroscopies and thermodynamic measurements.

For a model system consisting of a ferromagnetic layer coupled to a diluted, antiferromagnetic layer extensive Monte Carlo simulations are performed. Exchange bias is observed as a result of a domain state in the antiferromagnetic layer which develops during fiel cooling, carrying an irreversible domain state's magnetization. In agreement with recent experimental observations on Co/CoO bilayers a strong dependence of the exchange bias fiel on dilution of the antiferromagnet is found and it is shown that a variety of typical effects associated with exchange bias, such as positive bias, temperature, and time dependencies as well as the dependence on the thickness of the antiferromagnetic layer can be explained within our model.

We demonstrate injection, transport and detection of spins in spin valve arrays patterned in both copper based chemical vapor deposition (Cu-CVD) synthesized wafer scale single layer (SLG) and bilayer graphene (BLG). We observe spin relaxation times comparable to those reported for exfoliated graphene samples demonstrating that CVD specific structural differences such as nanoripples and grain boundaries do not limit spin transport in the present samples. Our observations make Cu-CVD graphene a promising material of choice for large scale spintronic applications. KEYWORDS Spin transport, Hanle precession, graphene, CVD growth, rippleHigh charge mobility, (1) small spin-orbit coupling, (2) negligible hyperfine interaction, (3) the electric field effect (4) and last but not least the ability to sustain large current densities (5) make graphene an exceptional material for spintronic applications. The demonstration of micrometer long spin relaxation length in exfoliated SLG and BLG even at room temperature (RT) (6)-(12) and spin relaxation times in the order of nanoseconds (11)-(12) may pave the way to realize several of the recently proposed spin based device concepts. (13)- (15) However, for realistic device applications it remains to be seen, if such impressive spin transport properties can also be achieved in wafer scale CVD graphene. Equally important, spin transport studies based on micromechanically exfoliated graphene sheets are often too slow for the quick exploration of the basic spin properties of graphene and for testing potential device architectures. The recent progress in the Cu-based CVD growth of graphene has a strong impact on charge based graphene device applications. (16) However, CVD graphene has a large number of structural differences when compared to exfoliated graphene such as grain boundaries, (17) defects like pentagons, heptagons, octagons, vacancies, 1D line charges (18) and in the case of bilayer graphene possibly interlayer stacking faults. (19)-(20) In addition, the current growth and transfer process introduces residual catalysts, wrinkles, quasi-periodic nanoripple arrays and new classes of organic residues. (19) Despite all of these defects, charge mobilities in CVD graphene field effect transistors (FETs) have been comparable to what has been reported for most exfoliated graphene FETs on Si/SiO 2 substrates. (21) 3 Whether this synthesis route will also play an important role for spin transport studies and large scale spin-based device applications depends on how the same defects affect the spin relaxation times.In this Letter, we demonstrate spin transport in Cu-CVD grown SLG and BLG transferred onto conventional Si/SiO 2 substrates and discuss the role of nano-ripples, a ubiquitous surface structure of Cu-CVD graphene (19) . The growth and transfer of large-scale Cu-CVD graphene are the same as in Ref.(17). By controlling the post-growth annealing time of CVD graphene, we can obtain films with SLG coverage up to 95% or additional BLG coverage up to 40%. The latter...

We present a new fabrication method of graphene spin-valve devices which yields enhanced spin and charge transport properties by improving both the electrode-to-graphene and graphene-to-substrate interface. First, we prepare Co/MgO spin injection electrodes onto Si ++ /SiO 2 . Thereafter, we mechanically transfer a graphene-hBN heterostructure onto the prepatterned electrodes. We show that room temperature spin transport in single-, bi-and trilayer graphene devices exhibit nanosecond spin lifetimes with spin diffusion lengths reaching 10 µm combined with carrier mobilities exceeding 20, 000 cm 2 /Vs.

The spin-dependent electronic structure of thin epitaxial films of magnetite, Fe 3 O 4 (111), has been investigated at room temperature by means of spin-, energy-, and angle-resolved photoemission spectroscopy. Near the Fermi energy E F a spin polarization of Ϫ(80Ϯ5)% is found. The spin-resolved photoemission spectra for binding energies between 1.5 eV and E F show good agreement with spin-split band energies from densityfunctional calculations.PACS number͑s͒: 75.70. Ak, 75.50.Bb, 75.70.Cn, 79.60.Bm The materials class of half-metallic ferromagnets ͑HMF's͒ has attracted renewed interest recently in the search for efficient spin polarizers in spin electronics.1 The intriguing feature of metallic conductivity for one spin component and semiconducting behavior for the other was in most cases theoretically predicted on the basis of electron band structure calculations. An experimental struggle extended over many years and is still ongoing to convincingly verify the truly intrinsic spin-dependent electronic structure of HMF's and consequently the high-spin polarization at the Fermi energy E F . The use of surface-sensitive measurements like spinpolarized photoemission, tunneling into superconductors, or superconducting point-contact spectroscopy imposed severe constraints in addition to problems with sample stoichiometry and homogeneity. In many cases the preparation of highquality thin films was indispensable instead of bulk single crystals which are believed to be superior. Thus, from the first theoretical prediction of, e.g., HMF behavior in Heusler alloys in 1983, 2 it took almost two decades to find evidence for spin polarization values at E F which come close to the expected ones.3 However, problems with the stoichiometry and especially surface composition of the films used are prevailing. [3][4][5] Besides the Heusler alloys, the majority of HMF's have been identified among transition metal oxides on the basis of the local spin-density approximation ͑LSDA͒ to the densityfunctional theory. Predictions have been made for Fe 3 O 4 , 6,7 CrO 2 , 8,9 manganites, 10,11 and the double perovskite Sr 2 FeMoO 6 .12 Only recently, values of the spin polarization of over 90% near E F were found for CrO 2 at 1.8 K using superconducting point-contact spectroscopy, 13,14 although values of 95% had been obtained earlier at 300 K at binding energies of 2 eV below E F using spin-polarized photoemission. 15 The most straightforward evidence of a minority spin gap and a concomitant 95% spin polarization near E F was obtained in La 0.7 Sr 0.3 MnO 3 at 40 K by means of spin-polarized photoemission spectroscopy. 16In this paper we present experimental evidence for the half-metallic ferromagnetic state of magnetite (Fe 3 O 4 ) by means of spin-and angle-resolved vacuum ultraviolet ͑VUV, hϭ21.2 eV͒ photoemission spectroscopy. Using epitaxial Fe 3 O 4 (111) films we obtain at room temperature a negative spin polarization of Ϫ(80Ϯ5)% at E F . This value agrees within 6% with the magnetization at 300 K of a thin Fe 3 O 4 film. 17 M...