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 fabricated NiFe2Ox thin films on MgAl2O4(001) substrates by reactive dc magnetron cosputtering varying the oxygen partial pressure during deposition. The fabrication of a variable material with oxygen deficiency leads to controllable electrical and optical properties which would be beneficial for the investigations of the transport phenomena and would, therefore, promote the use of such materials in spintronic and spin caloritronic applications. We used several characterization techniques in order to investigate the film properties, focusing on their structural, magnetic, electrical, and optical properties. From the electrical resistivity measurements we obtained the conduction mechanisms that govern the systems in high and low temperature regimes, extracting low thermal activation energies which unveil extrinsic transport mechanisms. The thermal activation energy decreases in the less oxidized samples revealing the pronounced contribution of a large amount of electronic states localized in the band gap to the electrical conductivity. Hall effect measurements showed the mixed-type semiconducting character of our films. The optical band gaps were determined via ultraviolet-visible spectroscopy. They follow a similar trend as the thermal activation energy, with lower band gap values in the less oxidized samples.

We investigate the dependence of magnetic properties on the post-annealing temperature/time, the thickness of soft ferromagnetic electrode and Ta dusting layer in the pinned electrode as well as their correlation with the tunnel magnetoresistance ratio, in a series of perpendicular magnetic tunnel junctions of materials sequence Ta/Pd/IrMn/CoFe/Ta(x)/CoFeB/MgO(y)/CoFeB(z)/Ta/Pd. We obtain a large perpendicular exchange bias of 79.6 kA/m for x = 0.3 nm. For stacks with z = 1.05 nm, the magnetic properties of the soft electrode resemble the characteristics of superparamagnetism. For stacks with x = 0.4 nm, y = 2 nm, and z = 1.20 nm, the exchange bias presents a significant decrease at post annealing temperature Tann = 330 • C for 60 min, while the interlayer exchange coupling and the saturation magnetization per unit area sharply decay at Tann = 340 • C for 60 min. Simultaneously, the tunnel magnetoresistance ratio shows a peak of 65.5% after being annealed at Tann = 300 • C for 60 min, with a significant reduction down to 10% for higher annealing temperatures (Tann ≥ 330 • C) and down to 14% for longer annealing times (Tann = 300 • C for 90 min). We attribute the large decrease of tunnel magnetoresistance ratio to the loss of exchange bias in the pinned electrode.

Recently, magnetic tunnel junctions with perpendicular magnetized electrodes combined with exchange bias films have attracted large interest. In this paper we examine the tunnel magnetoresistance of Ta/Pd/IrMn/Co-Fe/Ta/Co-Fe-B/MgO/Co-Fe-B/capping/Pd magnetic tunnel junctions in dependence on the capping layer, i.e., Hf or Ta. In these stacks perpendicular exchange bias fields of -500 Oe along with perpendicular magnetic anisotropy are combined. A tunnel magnetoresistance of (47.2 ± 1.4)% for the Hf-capped sample was determined compared to the Ta one (42.6 ± 0.7)% at room temperature. Interestingly, this observation is correlated to the higher boron absorption of Hf compared to Ta which prevents the suppression of ∆1 channel and leads to higher tunnel magnetoresistance values. Furthermore, the temperature dependent coercivities of the soft electrodes of both samples are mainly described by the Stoner-Wohlfarth model including thermal fluctuations. Slight deviations at low temperatures can be attributed to a torque on the soft electrode that is generated by the pinned magnetic layer system.

We present a systematic study of the magnetic proximity effect in Pt, depending on the magnetic moment and anisotropy of adjacent metallic ferromagnets. Element-selective x-ray resonant magnetic reflectivity measurements at the Pt absorption edge (11565 eV) are carried out to investigate the spin polarization of Pt in Pt/Co1-xFex bilayers. We observe the largest magnetic moment of (0.72 ± 0.03) µB per spin polarized Pt atom in Pt/Co33Fe67, following the Slater-Pauling curve of magnetic moments in Co-Fe alloys. In general, a clear linear dependence is observed between the Pt moment and the moment of the adjacent ferromagnet. Further, we study the magnetic anisotropy of the magnetized Pt which clearly adopts the magnetic anisotropy of the ferromagnet below. This is depicted for Pt on Fe(001) and on Co50Fe50(001), which have a 45 • relative rotation of the fourfold magnetocrystalline anisotropy.