We have observed that CoO films grown on different substrates show dramatic differences in their magnetic properties. Using polarization dependent x-ray absorption spectroscopy at the Co L2,3 edges, we revealed that the magnitude and orientation of the magnetic moments strongly depend on the strain in the films induced by the substrate. We presented a quantitative model to explain how strain together with the spin-orbit interaction determine the 3d orbital occupation, the magnetic anisotropy, as well as the spin and orbital contributions to the magnetic moments. Control over the sign and direction of the strain may therefore open new opportunities for applications in the field of exchange bias in multilayered magnetic films.The discovery of the exchange bias phenomenon in surface-oxidized cobalt particles about 50 years ago [1] marks the beginning of a new research field in magnetism. Since then several combinations of antiferromagnetic (AFM) and ferromagnetic (FM) thin film materials have been fabricated and investigated [2,3], motivated by the potential for applications in information technology. Numerous theoretical [4,5,6,7,8] and experimental [9,10,11,12,13,14] studies have been devoted to unravel the mechanism(s) responsible for exchange biasing. However, no conclusive picture has emerged yet. A major part of the problem lies in the fact that there is insufficient information available concerning the atomic and magnetic structure of the crucial interface between the AFM and FM material. The important issue of, for instance, spin reorientations in the AFM films close to the interface is hardly considered [15,16,17,18,19], and the role of epitaxial strain herein has not been discussed at all.In this paper we study the magnetic properties of CoO thin films epitaxially grown on MnO(100) and on Ag(100), as model systems for an AFM material under either tensile or compressive in-plane stress. Our objective is to establish how the magnetic anisotropy as well as the spin and orbital contributions to the magnetic moments depend on the lowering of the local crystal field symmetry by epitaxial strain. Using polarization dependent x-ray absorption spectroscopy (XAS) at the Co L 2,3 (2p → 3d) edges, we observe that the magnitude and orientation of the magnetic moments in the CoO/MnO(100) system are very different from those in the CoO/Ag(100). We present a quantitative model to calculate how local crystal fields together with the spin-orbit interaction determine the magnetic properties. to 10 −6 mbar. The base pressure of the MBE system is in the low 10 −10 mbar range. The thickness and epitaxial quality of the films are monitored by reflection high energy electron diffraction measurements. With the lattice constant of bulk Ag (4.09Å) being smaller than that of bulk CoO (4.26Å) and MnO (4.444Å), we find from x-ray diffraction that CoO on Ag is slightly compressed in-plane (a ≈ 4.235Å, a ⊥ ≈ 4.285Å), and from reflection high energy electron diffraction (RHEED) that CoO sandwiched by MnO is about 4% expanded in-plane (a ...

Thin films of PbTiO3, a classical ferroelectric, have been grown under tensile strain on single-crystal substrates of DyScO3. The films, of only 5 nm thickness, grow fully coherent with the substrate, as evidenced by synchrotron x-ray diffraction. A mapping of the reciprocal space reveals intensity modulations (satellites) due to regularly spaced polar domains in which the polarization appears rotated away from the substrate normal, characterizing a low-symmetry phase not observed in the bulk material. This could have important practical implications since these phases are known to be responsible for ultrahigh piezoelectric responses in complex systems.

We report on a X-ray absorption spectroscopic (XAS) study on a thin film of La0.7Ce0.3MnO3, a manganite which was previously only speculated to be an electron doped system. The measurements clearly show that the cerium is in the Ce(IV) valence state and that the manganese is present in a mixture of Mn 2+ and Mn 3+ valence states. These data unambiguously demonstrate that La0.7Ce0.3MnO3 is an electron doped colossal magnetoresistive manganite, a finding that may open up new opportunities both for device applications as well as for further basic research towards a better modelling of the colossal magnetoresistance phenomenon in these materials.PACS numbers: 78.70. Dm, 71.28.+d, 72.80.Ga, 75.30.Vn Hole doped rare-earth manganites of the form R 1−x A x MnO 3 (R = rare-earth, A = divalent cation) have been at the focus of attention in recent times in the field of ferromagnetic oxides.1,2 The interest in these compounds stems from a variety of reasons. These compounds exihibit a large magnetoresistance, coined as 'colossal magnetoresistance' (CMR), close to their ferromagnetic transition temperature (T c ) which makes them potential candidates for device applications. These materials exhibit a strong interplay between spin, charge and orbital degrees of freedom, due to the competition of the various relevant energy scales that are of comparable magnitude. All these give rise to a wide variety of phenomena such as electronic phase separation, charge ordering, spin glass order and half metallicity.2 It is therefore of prime fundamental interest to study the rich phase diagram of these compounds as a function of doping x and size of the R/A cation. 3The basic physics of the hole doped rare-earth manganites can be understood from an interplay of a strong Hund's rule coupling in the manganese and the JahnTeller distortion. 3+ is a Jahn-Teller ion. Thus, the basic physics in terms of Hund's rule coupling and JahnTeller effect could operate in the electron doped phase as well. The existence of an electron doped manganite is not merely of academic interest since it also opens up possibilities for fabricating novel bipolar devices using the electron and hole doped manganites where both spin and charge are utilized.The crucial issue that we have to address now is whether it is really possible to electron dope LaMnO 3 . One compound, which displays properties remarkably similar to La 0.7 Ca 0.3 MnO 3 , is the cerium doped manganite La 0.7 Ce 0.3 MnO 3 . La 0.7 Ce 0.3 MnO 3 has a ferromagnetic metallic ground state with T c ∼ 250 K. 6,7,8The ferromagnetic transition is accompanied by a metalinsulator transition and the system has a magnetoresistance (ρ(0) − ρ(H)/ρ(0)) in excess of 70% at a field of 1.5 T.7 It has been shown very recently that a tunnel junction made of the hole doped La 0.7 Ca 0.3 MnO 3 and La 0.7 Ce 0.3 MnO 3 exhibits rectifying characteristics 9 in the polaronic insulating state at temperatures T > T c . While this result may suggest that cerium doping drives the manganese in a mixture of Mn 2+ and Mn 3+ vale...

We describe a possible pathway to new magnetic materials with no conventional magnetic elements present. The substitution of nitrogen for oxygen in simple nonmagnetic oxides leads to holes in N 2p states which form local magnetic moments. Because of the very large Hund's rule coupling of Nitrogen and O 2p electrons and the rather extended spatial extent of the wave functions these materials are predicted to be ferromagnetic metals or small band gap insulators. Experimental studies support the theoretical calculations with regard to the basic electronic structure and the formation of local magnetic moments. It remains to be seen if these materials are magnetically ordered and, if so, below what temperature.

We have detected strong dichroism in the Ni L-2,L-3 x-ray absorption spectra of a monolayer NiO film. The dichroic signal appears to be very similar to the magnetic linear dichroism observed for thicker antiferromagnetic NiO films. Detailed analysis reveals, however, that the dichroism is caused by crystal-field effects in the monolayer film, which is a nontrivial effect because the high spin Ni 3d(8) ground state is not split by low-symmetry crystal fields. We present a practical method for identifying the independent magnetic and crystal-field contributions to the linear dichroic signal in spectra of NiO films with arbitrary thicknesses and lattice strains. Our findings are also relevant for 3d(5) and 3d(3) systems such as LaFeO3, Fe2O3, VO, LaCrO3, Cr2O3, and Mn4+ thin films