XMCD studies of thin Co films on BaTiO3_3

Different layer thicknesses of Cobalt ranging from 2.6 {\AA} (1.5 ML) up to 55 {\AA} (30.5 ML) deposited on ferroelectric BaTiO$_3$ have been studied regarding their magnetic behavior. The layers have been characterized using XMCD spectroscopy at remanent magnetization. After careful data analysis the magnetic moments of the Cobalt could be determined using the sum rule formalism. There is a sudden and abrupt onset in magnetism starting at thicknesses of 9 {\AA} (5 ML) of Cobalt for measurements at 120 K and of 10 {\AA} (5.5 ML) if measured at room temperature. Initial island growth and subsequent coalescence of Co on BaTiO$_3$ is suggested to explain the sudden onset. In that context, no magnetically dead layers are observed.Comment: 9 pages, 5 figures, submitted to J. Phys. Condens. Matte

Graphene-based synthetic antiferromagnets and ferrimagnets

Graphene-spaced magnetic systems with antiferromagnetic exchange-coupling offer exciting opportunities for emerging technologies. Unfortunately, the in-plane graphene-mediated exchange-coupling found so far is not appropriate for realistic exploitation, due to being weak, being of complex nature, or requiring low temperatures. Here we establish that ultra-thin Fe/graphene/Co films grown on Ir(111) exhibit robust perpendicular antiferromagnetic exchange-coupling, and gather a collection of magnetic properties well-suited for applications. Remarkably, the observed exchange coupling is thermally stable above room temperature, strong but field controllable, and occurs in perpendicular orientation with opposite remanent layer magnetizations. Atomistic first-principles simulations provide further ground for the feasibility of graphene-spaced antiferromagnetic coupled structures, confirming graphene's direct role in sustaining antiferromagnetic superexchange-coupling between the magnetic films. These results provide a path for the realization of graphene-based perpendicular synthetic antiferromagnetic systems, which seem exciting for fundamental nanoscience or potential use in spintronic devices

Spin re-orientation induced anisotropic magnetoresistance switching in LaCo0.5_{0.5}Ni0.5_{0.5}O3−δ_{3-\delta} thin films

Realization of novel functionalities by tuning magnetic interactions in rare earth perovskite oxide thin films opens up exciting technological prospects. Strain-induced tuning of magnetic interactions in rare earth cobaltates and nickelates is of central importance due to their versatility in electronic transport properties. Here we reported the spin re-orientation induced switching of anisotropic magnetoresistance (AMR) and its tunability with strain in epitaxial LaCo$_{0.5}$Ni$_{0.5}$O$_{3-\delta}$ thin films across the ferromagnetic transition. Moreover, with strain tuning, we could observe a two-fold to four-fold symmetry crossover in AMR across the magnetic transition temperature. The magnetization measurements revealed an onset of ferromagnetic transition around 50 K, and a further reduction in temperature showed a subtle change in the magnetization dynamics, which reduced the ferromagnetic long-range ordering and introduced glassiness in the system. X-ray absorption and X-ray magnetic circular dichroism spectroscopy measurements over Co and Ni L edges revealed the Co spin state transition below the magnetic transition temperature leading to the AMR switching and also the presence of Ni$^{2+}$ and Co$^{4+}$ ions evidencing the charge transfer from Ni to Co ions. Our work demonstrated the tunability of magnetic interactions mediated electronic transport in cobaltate-nickelate thin films, which is relevant in understanding Ni-Co interactions in oxides for their technological applications such as in AMR sensors

Independent Tuning of Optical Transparency Window and Electrical Properties of Epitaxial SrVO3 Thin Films by Substrate Mismatch

Transparent metallic oxides are pivotal materials in information technology, photovoltaics, or even in architecture. They display the rare combination of metallicity and transparency in the visible range because of weak interband photon absorption and weak screening of free carriers to impinging light. However, the workhorse of current technology, indium tin oxide (ITO), is facing severe limitations and alternative approaches are needed. AMO perovskites, M being a nd transition metal, and A an alkaline earth, have a genuine metallic character and, in contrast to conventional metals, the electron-electron correlations within the nd band enhance the carriers effective mass (m*) and bring the transparency window limit (marked by the plasma frequency, ω*) down to the infrared. Here, it is shown that epitaxial strain and carrier concentration allow fine tuning of optical properties (ω*) of SrVO films by modulating m* due to strain-induced selective symmetry breaking of 3d-t(xy, yz, xz) orbitals. Interestingly, the DC electrical properties can be varied by a large extent depending on growth conditions whereas the optical transparency window in the visible is basically preserved. These observations suggest that the harsh conditions required to grow optimal SrVO films may not be a bottleneck for their future application

Data to support study of Spin-Crossover in a New Iron(II)/Di(pyrazolyl)pyridine Complex with a Terpyridine Embrace Lattice

[FeL2]X2 ( L = 2,6-di{4-fluoropyrazol-1-yl}pyridine) exhibit hysteretic spin-transitions at T½ = 164 (X = BF4) and 148 K (X = ClO4). The perchlorate salt shows efficient TIESST below 120 K, and was characterized in its thermally trapped high-spin form, as well as in its thermodynamic high- and low-spin states

Data to support The Effect of Inert Dopant Ions on Spin-Crossover Materials is not Simply Controlled by Chemical Pressure

The spin-crossover temperature in [FexRu(1-x)(bpp)2][BF4]2 increases with increased ruthenium doping, which reflects a subtle interplay between the [Ru(bpp)2]2+ dopant molecules and the [Fe(bpp)2]2+ switching centres in the lattice

Data to support study of Di-Iron(II) [2+2] Helicates of Bis-(Dipyrazolylpyridine) Ligands – the Influence of the Ligand Linker Group on Spin State Properties

A diiron(II) complex has been crystallised in three different helicate conformations, which differ in the torsions of the butane-1,4-diyl ligand linker groups. The crystals exhibit a range of spin state properties, including stepwise spin-crossover of the two iron atoms. A related ligand with a rigid pyrid-2,6-diyl spacer forms more a distorted, high-spin diiron(II) helicate structure

Author Correction: Non-local effect of impurity states on the exchange coupling mechanism in magnetic topological insulators

A Correction to this paper has been published: https://doi.org/10.1038/s41535-021-00314-

On the Role of Interfaces on Spin Transport in Magnetic Insulator/Normal Metal Heterostructures

Spin currents have emerged as a new tool in spintronics, with promises of more efficient devices. A pure spin current can be generated in a nonmagnetic metallic (NM) layer by a charge current (spin Hall effect). When the NM layer is placed in contact with a magnetic material, a magnetoresistance (spin Hall magnetoresistance) develops in the former via the inverse spin Hall effect (ISHE). In other novel spin‐dependent phenomena, such as spin pumping or spin Seebeck effect, spin currents are generated by magnetic resonance or thermal gradients and detected via ISHE in a neighboring normal metal layer. All cases involve spin transport across interfaces between nonmagnetic metallic layers and magnetic materials; quite commonly, magnetic insulators. The structural, compositional, and electronic differences between these materials and their integration to form an interface, challenge the control and understanding of the spin transport across it, which is known to be sensitive to sub‐nanometric interface features. Here, the authors review the tremendous progress in material's science achieved during the last few years and illustrate how the spin Hall magnetoresistance can be used as a probe for surface magnetism. The authors end with some views on concerted actions that may allow further progress.Peer reviewe