The DEIMOS (Dichroism Experimental Installation for Magneto-Optical Spectroscopy) beamline was part of the second phase of the beamline development at French Synchrotron SOLEIL (Source Optimisée de Lumière à Energie Intermédiaire du LURE) and opened to users in March 2011. It delivers polarized soft x-rays to perform x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and x-ray linear dichroism in the energy range 350-2500 eV. The beamline has been optimized for stability and reproducibility in terms of photon flux and photon energy. The main end-station consists in a cryo-magnet with 2 split coils providing a 7 T magnetic field along the beam or 2 T perpendicular to the beam with a controllable temperature on the sample from 370 K down to 1.5 K.

The strong coupling between antiferromagnetism and ferroelectricity at room temperature found in BiFeO3 generates high expectations for the design and development of technological devices with novel functionalities. However, the multi-domain nature of the material tends to nullify the properties of interest and complicates the thorough understanding of the mechanisms that are responsible for those properties. Here we report the realization of a BiFeO3 material in thin film form with single-domain behaviour in both its magnetism and ferroelectricity: the entire film shows its antiferromagnetic axis aligned along the crystallographic b axis and its ferroelectric polarization along the c axis. With this we are able to reveal that the canted ferromagnetic moment due to the Dzyaloshinskii–Moriya interaction is parallel to the a axis. Furthermore, by fabricating a Co/BiFeO3 heterostructure, we demonstrate that the ferromagnetic moment of the Co film does couple directly to the canted moment of BiFeO3.

We report on a combined soft x-ray absorption and magnetic circular dichroism (XMCD) study at the Co-L3,2 on the hybrid 3d/5d solid state oxide Sr2Co0.5Ir0.5O4 with the K2NiF4 structure. Our data indicate unambiguously a pure high spin state (S = 2) for the Co 3+ (3d 6 ) ions with a significant unquenched orbital moment Lz/2Sz = 0.25 despite the sizeable elongation of the CoO6 octahedra. Using quantitative model calculations based on parameters consistent with our spectra, we have investigated the stability of this high spin state with respect to the competing low spin and intermediate spin states.PACS numbers: 71.70. Ch, 75.47.Lx, 78.70.Dm, 72.80.Ga Cobalt compounds have aroused a great deal of attention in the scientific community because of the complex and large diversity of physical phenomena displayed, including metal-insulating transitions 1-3 , superconductivity 4 , large magneto-resistance 5 and high thermoelectric power 6 . This richness of electronic and magnetic properties is closely related not only to the possibility of stabilizing cobalt in different valence states but also to its ability to present different spin states, the so-called spinstate degree of freedom 7,8 . For example, in an octahedral coordination, Co 3+ ions, which have the d 6 configuration, can exist in three possible spin states: a high spin (HS) state (S = 2, t 4 2g e 2 g ), a low spin (LS) state (S = 0, t 6 2g e 0 g ) and even an intermediate spin (IS) state (S = 1, t 5 2g e 1 g ) 7,9,10 . This spin state degree of freedom is evident in LaCoO 3 where the Co 3+ ions have a non-magnetic LS ground state and undergo a gradual transition with increasing temperature to a magnetic spin state [11][12][13] . The nature of the magnetic spin state (IS or HS) was heavily disputed in literature for over four decades, till an XMCD study clearly demonstrated it to be HS 10 . Calculations of the Co 3+ energy level diagram show that the LS (HS) state can be stabilized by a large (small) value of the crystal field 10Dq. The IS is always higher in energy for CoO 6 octahedra close to regular, like in LaCoO 3 10 .However, the IS state, with one electron in the e g states, is Jahn-Teller active and, hence, can gain energy and become the ground state in the presence of a sufficiently large distortion of the local structure 14 . For this reason the spin state of the Co 3+ ions in layered cobaltates, where the elongated distortion of the CoO 6 octahedra favors and may stabilize the IS state, have been subject of intense debate. In the case of layered La 2−x Sr x CoO 4 , contradicting scenarios for the Co 3+ ions were considered to interpret the complex structural, magnetic and transport properties of the system as a function of Sr doping: LS Co 3+ , IS Co 3+ 15-17 , HS-to-IS transition 18 , and mixing of HS/IS 19,20 . Only recently the spin state of Co 3+ in layered La 2−x Sr x CoO 4 was demonstrated by X-ray absorption spectroscopy (XAS) studies to be LS 21,22 for x = 0.5 and a mixture of LS/HS for x ≥ 1 22-24 . Band formation has been proposed to p...

The fundamental important and technologically widely employed exchange bias effect occurs in general in bilayers of magnetic thin films consisting of antiferromagnetic and ferromagnetic layers where the hard magnetization behavior of an antiferromagnetic thin film causes a shift in the magnetization curve of a soft ferromagnetic film. The minimization of the single magnetic grain size to increase the storage density and the subsequent demand for magnetic materials with very high magnetic anisotropy requires a system with high H EB . Here we report an extremely high H EB of 4 Tesla observed in a single amorphous DyCo 4 film close to room temperature. The origin of the exchange bias can be associated with the variation of the magnetic behavior from the surface towards the bulk part of the film revealed by X-ray absorption spectroscopy and X-ray magnetic circular dichroism techniques utilizing the bulk sensitive transmission and the surface sensitive total electron yield modes. The competition between the atomic exchange coupling in the single film and the Zeeman interaction lead to an intrinsic exchanged coupled system and the so far highest exchange bias effect H EB = 4 Tesla reported in a single film, which is accommodated by a partial domain wall formation.Exchange bias effect (EB) was discovered in 1956 by Meiklejohn and Bean when studying Co particles embedded in their native antiferromagnetic oxide 1 . It is generally considered to form from an uncompensated spin configuration at the ferromagnetic/antiferromagnetic (FM/AF) interface 2,3 , as it is the case in small particles, inhomogeneous materials, FM films on AF single crystals and FM on AF thin films 4 with frozen and rotatable spins at their interfaces [5][6][7][8][9] . Phenomenologically, the EB effect in FM/AF systems displays a shift of the hysteresis by an EB field H EB that is achieved by a magnetic field cooling procedure down to the Néel temperature T N of the AF. The experimentally observed value of the H EB in FM/AF systems, however, is in general several orders of magnitude below the theoretical prediction for a perfect EB system 10 . This discrepancy resulted in a heavy debate and the development of sophisticated models for the explanation of the origin of the EB effect and its drastic reduction of the EB effect in real EB systems 4,11,12 . Besides the classical system of AF/FM interfaces, EB and related effects have been observed also in other types of samples, e.g. involving ferrimagnets (FI): AF/FI 13 , FI/FM 14-16 and lately also in FI/FI 17 with a compensated spin structures at the interface. Transition Metal-Rare Earth (TM-RE) alloys, in particular, are nowadays suggested to used as FI materials in magnetic hybrid structures exhibiting strong EB effects 18 . Besides an interfacial exchange between two chemically and magnetically different compositions, a physically induced magnetic phase deviation from the bulk to the surface may also results into an exchange bias effect although there is no obvious chemical interface in the sample. The...

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