The spin polarization of Pt in Pt/NiFe2O4 and Pt/Fe bilayers is studied by interface-sensitive x-ray resonant magnetic reflectivity to investigate static magnetic proximity effects. The asymmetry ratio of the reflectivity was measured at the Pt L3 absorption edge using circular polarized x-rays for opposite directions of the magnetization at room temperature. The results of the 2% asymmetry ratio for Pt/Fe bilayers are independent of the Pt thickness between 1.8 and 20 nm. By comparison with ab initio calculations, the maximum magnetic moment per spin polarized Pt atom at the interface is determined to be (0.6 ± 0.1) µB for Pt/Fe. For Pt/NiFe2O4 the asymmetry ratio drops below the sensitivity limit of 0.02 µB per Pt atom. Therefore, we conclude, that the longitudinal spin Seebeck effect recently observed in Pt/NiFe2O4 is not influenced by a proximity induced anomalous Nernst effect. In spintronics1 and spin caloritronics 2 pure spin currents can be generated in ferromagnetic insulators (FMIs) by spin pumping 3 , the spin Hall effect 4 and the spin Seebeck effect 5 . Since these spin currents play an important role in spintronic applications, an understanding of the generation, manipulation and detection of spin currents is an important topic of research. A common spin current detection technique uses a nonferromagnetic metal (NM) thin film grown on a ferromagnet (FM). The inverse spin Hall effect 6 converts the spin current into a transverse voltage in the NM. Pt is commonly used as NM due to its large spin Hall angle 7 , but has generated some controversy in the interpretation because of its closeness to the Stoner criterion, which can induce, e.g., Hall or Nernst effects due to the proximity to the FM 8 .For a quantitative evaluation of the spin Seebeck effect (thermal generation of spin currents) one has to exclude or separate various parasitic effects. It is reported 5 that in transverse spin Seebeck experiments a spin current is generated perpendicular to the applied temperature gradient which is typically aligned in-plane. For ferromagnetic metals (FMMs) with magnetic anisotropy, the planar Nernst effect 9 can contribute 10 due to the anisotropic magnetothermopower. Furthermore, out-of-plane temperature gradients due to heat flow into the surrounding area 11 or through the electrical contacts 12 can induce an anomalous Nernst effect (ANE) [13][14][15] or even an unintended longitudinal spin Seebeck effect as recently reported 16 .The longitudinal spin Seebeck effect (LSSE) 17 describes a spin current that is generated parallel to the temperature gradient, which is typically aligned outof-plane to drive the parallel spin current directly into the NM material. For FMMs or semiconducting ferromagnets an ANE can also contribute to the measured voltage 18 . Furthermore, for NM materials close to the Stoner criterion a static magnetic proximity effect in the NM at the NM/FMI interface can lead to a proximity induced ANE 8 . If an in-plane temperature gradient is applied, a proximity induced planar Nernst effect ...

The magnetic structure of the Eu 2+ moments in the superconducting EuFe2(As1−xPx)2 sample with x = 0.15 has been determined using element specific x-ray resonant magnetic scattering. Combining magnetic, thermodynamic and scattering measurements, we conclude that the long range ferromagnetic order of the Eu 2+ moments aligned primarily along the c axis coexists with the bulk superconductivity at zero field. At an applied magnetic field ≥ 0.6 T, superconductivity still coexists with the ferromagnetic Eu 2+ moments which are polarized along the field direction. We propose a spontaneous vortex state for the coexistence of superconductivity and ferromagnetism in EuFe2(As0.85P0.15)2.

We have used in-field neutron and x-ray single-crystal diffraction to measure the incommensurability ␦ of the crystal and magnetic structures of multiferroic TbMnO 3 . We show that the flop in the electric polarization at the critical field H C , for field H along the a and b axes, coincides with a first-order transition to a commensurate phase with propagation vector = ͑ 0, 1 4 ,0 ͒ . In-field x-ray diffraction measurements show that the quadratic magnetoelastic coupling breaks down with applied field as shown by the observation of the first harmonic lattice reflections above and below H C . This indicates that magnetic field induces a linear magnetoelastic coupling. DOI: 10.1103/PhysRevB.73.020102 PACS number͑s͒: 77.80.Bh, 64.70.Kb, 75.25.ϩz, 77.22.Ej Control of the spontaneous ferroelectric polarization ͑P s ͒ with an external magnetic field ͑H͒ in a material opens the opportunity for new types of magnetoelectric devices. The realization of such devices is based on multiferroic materials in which magnetism and ferroelectricity are strongly coupled. While available multiferroics are limited, it has been shown that frustrated spin materials may offer a unique class of enhanced multiferroics. [1][2][3] In one of these materials, TbMnO 3 , we find that multiferroic behavior arises as a consequence of the release of frustration with H. Here ferroelectricity arises below the Néel temperature ͑T N ͒ from a coupling to the lattice of an incommensurate ͑IC͒ modulation of the magnetic structure ͓Fig. 1͑a͔͒ that is caused from frustration in the ordering of the Mn d orbitals. 1,3 In this communication we show that magnetic field releases this frustration, inducing a linear magnetoelastic coupling, so that ferroelectricity is no longer a secondary effect. The linear magnetoelastic coupling drives a magnetostructural transition from an IC phase, which has P s along the c axis ͑P ʈ c͒, to a commensurate ͑C͒ phase with P s along the a axis ͑P ʈ a͒.In TbMnO 3 , when a magnetic field is applied along the b axis ͑H ʈ b͒ at 2 K, parallel to the direction of the IC magnetic modulation ͓see Fig. 1͑a͔͒, the electric polarization of the lattice flops from P ʈ c to P ʈ a at the critical field H C b ϳ 4.5 T ͓Fig. 2͑d͔͒. When field is applied along the a axis ͑H ʈ a͒, perpendicular to the magnetic modulation, a similar flop is found but at a higher critical field, H C a ϳ 9 T ͓Fig. 2͑a͔͒. Recently there have been a number of examples of magnetoelastic coupling in complex multiferroic oxides such as TbMn 2 O 5 which exhibit a reversable polarization switch with applied field, 4 and hexagonal HoMnO 3 where one magnetic phase is selected over another by applying an electric field.5 However, TbMnO 3 is unique as it is the only known example of a material that exhibits a field-induced flop of its polarization.In TbMnO 3 the staggered ordering of Mn 3+ 3d 3x 2 −r 2 /3d 3y 2 −r 2 orbitals as found in LaMnO 3 is frustrated partly due to the small ionic size of Tb 3+3 . This leads to an IC spin ordering which drives a ferroelectric lattice...

Resonant x-ray diffraction performed at the L(II) and L(III) absorption edges of Ru has been used to investigate the magnetic and orbital ordering in Ca2RuO4 single crystals. A large resonant enhancement due to electric dipole 2p-->4d transitions is observed at the wave-vector characteristic of antiferromagnetic ordering. Besides the previously known antiferromagnetic phase transition at T(N)=110 K, an additional phase transition, between two paramagnetic phases, is observed around 260 K. Based on the polarization and azimuthal angle dependence of the diffraction signal, this transition can be attributed to orbital ordering of the Ru t(2g) electrons. The propagation vector of the orbital order is inconsistent with some theoretical predictions for the orbital state of Ca2RuO4.

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