The cheap stainless commodity steel AISI 304, which basically consists of Fe, Ni, and Cr, was surface-oxidized by exposure to Cl2 gas. This treatment turned AISI 304 steel into an efficient electrocatalyst for water splitting at pH 7 and pH 13. The overpotential of the anodic oxygen evolution reaction (OER), which typically limits the efficiency of the overall water-splitting process, could be reduced to 260 mV at 1.5 mA/cm2 in 0.1 M KOH. At pH 7, overpotentials of 500–550 mV at current densities of 0.65 mA/cm2 were achieved. These values represent a surprisingly good activity taking into account the simplicity of the procedure and the fact that the starting material is virtually omnipresent. Surface-oxidized AISI 304 steel exhibited outstanding long-term stability of its electrocatalytic properties in the alkaline as well as in the neutral regime, which did not deteriorate even after chronopoteniometry for 150 000 s. XPS analysis revealed that surface oxidation resulted in the formation of Fe oxide and Cr oxide surface layers with a thickness in the range of a few nanometers accompanied by enrichment of Cr in the surface layer. Depending on the duration of the Cl2 treatment, the purity of the Fe oxide/Cr oxide mixture lies between 95% and 98%. Surface oxidation of AISI 304 steel by chlorination is an easy and scalable access to nontoxic, cheap, stable, and efficient electrocatalysts for water splitting.

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 ...

We identify and investigate thermal spin transport phenomena in sputter-deposited Pt/NiFe2O4-x (4 ≥ x ≥ 0) bilayers. We separate the voltage generated by the spin Seebeck effect from the anomalous Nernst effect contributions and even disentangle the intrinsic anomalous Nernst effect (ANE) in the ferromagnet (FM) from the ANE produced by the Pt that is spin polarized due to its proximity to the FM. Further, we probe the dependence of these effects on the electrical conductivity and the band gap energy of the FM film varying from nearly insulating NiFe2O4 to metallic Ni33Fe67. A proximity-induced ANE could only be identified in the metallic Pt/Ni33Fe67 bilayer in contrast to Pt/NiFe2Ox (x > 0) samples. This is verified by the investigation of static magnetic proximity effects via x-ray resonant magnetic reflectivity.In the emerging fields of spintronics Pt is employed frequently for generating and detecting pure spin currents, if adjacent to an FMI, although the possibility of magnetic proximity effects (MPEs) has to be taken into account. Due to its close vicinity to the Stoner criterion [11] the FM can potentially generate a Pt spin polarization at the interface. Consequently, this might induce additional parasitic effects preventing the correct interpretation of the measured ISHE voltage. Therefore, a comprehensive investigation regarding the magnetic properties of the NM/FM interface is required to distinguish the contributions of such parasitic voltages from the ISHE voltage generated by a pure spin current.In the case of SSE, the driving force for the spin current in the FM or FMI is a temperature gradient. When a spin current is generated parallel to a temperature gradient, it is generally attributed to the longitudinal spin Seebeck effect (LSSE) [4,5]. However, when using the ISHE in an adjacent NM for the spin current detection, not only a proximity-induced ANE [12] can contaminate the LSSE signal, but also an additional intrinsic ANE contribution could be present in case of studying ferromagnetic metals (FMMs) or semiconducting ferro(i)magnets [13,14]. Mainly NM/FMI bilayers have been investigated, while LSSE studies on NM/FMM are quite rare.However, Ramos et al. [14][15][16][17] and Wu et al. [18] individually investigated the LSSE in magnetite, which is conducting at room temperature (RT) and, thus, has an intrinsic ANE contribution. They identified the LSSE in Pt/Fe 3 O 4 [14] and CoFeB/Fe 3 O 4 bilayers [18] by using temperatures below the conductor-insulator transition of magnetite (Verwey transition at 120 K) in order to exclude any intrinsic ANE contribution. Ramos et al. further investigated the ANE in bulk magnetite without any Pt [15] and concluded that the ANE contributions for Pt/Fe 3 O 4 bilayers and multilayers should be quite small [16,17]. In addition, Lee et al. [19] and Uchida et al. [20,21] discussed that in Pt/FMM multilayers both LSSE and ANE contribute, but did not disentangle the effects quantitatively. Hence, a clear quantitative disentanglement of the LSSE in the FMM [22], the ...

We present x-ray resonant magnetic reflectivity (XRMR) as a very sensitive tool to detect proximity induced interface spin polarization in Pt/FM heterostructures. Different XRMR experiments are carried out and the results are evaluated for their dependence on the magneto-optical depth profile, the photon energy, the optical parameters, and the ferromagnetic material. We demonstrate that a detailed analysis of the reflected x-ray intensity gives insight into the spatial distribution of the spin polarization of a nonmagnetic metal across the interface to a ferromagnetic layer. The evaluation of the experimental results with simulations based on optical data from ab initio calculations provides the induced magnetic moment per Pt atom in the spin-polarized volume adjacent to the ferromagnet. For a series with different ferromagnetic materials consisting of Pt/Fe, Pt/Ni 33 Fe 67 , Pt/Ni 81 Fe 19 (permalloy), and Pt/Ni bilayers we find the largest spin polarization in Pt/Fe and a much smaller magnetic proximity effect in Pt/Ni. Additional XRMR experiments with varying photon energy are in good agreement with the theoretical predictions for the energy dependence of the magneto-optical parameters and allow identifying the optical dispersion δ and absorption β across the Pt L 3 -absorption edge.

The longitudinal spin Seebeck effect is detected in sputter-deposited NiFe2O4 films using Pt as a spin detector and compared to previously investigated NiFe2O4 films prepared by chemical vapor deposition. Anomalous Nernst effects induced by the magnetic proximity effect in Pt can be excluded for the sputter-deposited NiFe2O4 films down to a certain limit, since x-ray resonant magnetic reflectivity measurements show no magnetic response down to a limit of 0.04 µB per Pt atom comparable to the case of the chemically deposited NiFe2O4 films. These differently prepared films have various thicknesses. Therefore, we further studied Pt/Fe reference samples with various Fe thicknesses and could confirm that the magnetic proximity effect is only induced by the interface properties of the magnetic material.Index Terms-magnetic proximity effect, spin Seebeck effect, magnetic insulators, x-ray resonant magnetic reflectivity.