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Ultrafast studies of magnetization dynamics have revealed fundamental processes that govern spin dynamics, and the emergence of time-resolved x-ray techniques has extended these studies to long-range spin structures that result from interactions with competing symmetries. By combining time-resolved resonant x-ray scattering and ultrafast magneto-optical Kerr studies, we show that the dynamics of the core spins in the helical magnetic structure occur on much longer time scales than the excitation of conduction electrons in the lanthanide metal Dy. The observed spin behavior differs markedly from that observed in the ferromagnetic phase of other lanthanide metals or transition metals and is strongly dependent on temperature and excitation fluence. This unique behavior results from coupling of the real-space helical spin structure to the shape of the conduction electron Fermi surface in momentum space, which creates a bottleneck in spin scattering events that transfer the valence excitation to the core spins. The dependence of the dynamics on the intersite interactions renders the helical ordering much more robust to perturbations than simple ferromagnetic or antiferromagnetic ordering, where dynamics are driven primarily by on-site interactions. [ABSTRACT FROM AUTHOR]

We report a simultaneous investigation of 3d and 4ƒ magnetic moments by exploring the Fe-L2,3 and Dy-M4,5 electron energy-loss edges of a DyFe2/YFe2 superlattice using the energy-loss magnetic chiral dichroism (EMCD) technique. Specific EMCD sum rules for M4,5 edges were established and carefully applied to the dichroic signal at Dy-M4,5 edges, giving an orbital to the effective spin moment ratio of 5.1±1.8. With dynamic diffraction effects considered, the opposite signs of Fe-L3 and Dy-M5 dichroic peaks unambiguously indicate the antiparallel alignment of net Fe 3d and Dy 4ƒ moments. The EMCD technique is shown to be an effective tool to locally characterize the 4ƒ moment of rare earth elements and study 3d-4ƒ moment coupling. [ABSTRACT FROM AUTHOR]

Using time-resolved x-ray diffraction, we demonstrate the manipulation of the picosecond strain response of a metallic heterostructure consisting of a dysprosium (Dy) transducer and a niobium (Nb) detection layer by an external magnetic field. We utilize the first-order ferromagnetic-antiferromagnetic phase transition of the Dy layer, which provides an additional large contractive stress upon laser excitation compared to its zero-field response. This enhances the laser-induced contraction of the transducer and changes the shape of the picosecond strain pulses driven in Dy and detected within the buried Nb layer. Based on our experiment with rare-earth metals we discuss required properties for functional transducers, which may allow for novel field-control of the emitted picosecond strain pulses., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)

The formation of two-dimensional oxide dodecagonal quasicrystals as well as related complex approximant phases was recently reported in thin films derived from BaTiO 3 or SrTiO 3 perovskites deposited on (111)-oriented Pt single crystals. Here, we use an all-thin-film approach in which the single crystal is replaced by a 10 nm thick Pt(111) buffer layer grown by molecular beam epitaxy on an Al 2 O 3 (0001) substrate. An ultra-thin film of SrTiO 3 was subsequently deposited by pulsed laser deposition. The film stacking and structure are fully characterized by diffraction and microscopy techniques. We report the discovery of two new complex phases obtained by reduction of this system through high temperature annealing under ultrahigh vacuum conditions. The formation of a new large square approximant with a lattice parameter equal to 44.4 Å is evidenced by low-energy electron diffraction and scanning tunneling microscopy (STM). Additionally, a new 2D hexagonal approximant phase with a lattice parameter of 28 Å has been observed depending on the preparation conditions. Both phases can be described by two different tilings constructed with the same basic square, triangle and rhombus tiles possessing a common edge length of about 6.7 Å. Using the tiling built from high resolution STM images, we propose an atomic model for each approximant which accounts for the experimental observations. Indeed, the STM images simulated using these models are found to be in excellent agreement with the experimental ones, the bright protrusions being attributed to the topmost Sr atoms. In addition our theoretical approach shows that the adhesion of the oxide layer is rather strong (-0.30 eV Å -2 ). This is attributed to charge transfer, from the most electropositive elements (Sr and Ti) to the most electronegative ones (Pt and O), and to hybridization with Pt-states. Density of states calculations indicate differences in the electronic structure of the two approximants, suggesting different chemical and physical properties. This all-thin-film approach may be useful to explore the formation of complex two-dimensional oxide phases in other metal-oxide combinations.

The strongly magnetostrictive TbFe 2 compound has been epitaxially grown on Z-cut Lithium Niobate (LiNbO 3 ) substrates after the deposition of various buffer layers (Mo, Ti and Ti/Mo). Detailed and combined RHEED and x-ray analysis permitted to unravel the in-plane and relative orientation relationships (OR) of the different materials in the system. Despite the use of different templates with different structural orders, similar final OR are eventually found between the piezoelectric substrate and the magnetic layer. The structural and magnetic properties are analyzed in order to get a TbFe 2 layer of optimum quality to build a magnetostrictive/piezoelectric hybrid system with efficient strain mediated coupling. Such systems are of interest for the development of magnetic sensors as well as for the electric control of magnetization.

The TbFe 2 compound has been deposited by molecular beam epitaxy on lithium niobate (LN) substrates with different orientations (LN Z-, 128 Y- and 41 Y-cuts). Despite the challenging growth on these unconventional substrates, crystalline TbFe 2 films (as a single orientated domain or with a limited number of orientations) of reasonable structural quality could be obtained after the deposition of a Mo buffer layer. Detailed and combined RHEED and x-ray analysis permitted to unravel the complex Mo and TbFe 2 crystal orientations and to reveal common 3D orientation relationships between the different lattices, whatever the initial LN cut. The magnetic properties and especially the magnetic anisotropy have been investigated in taking magnetocrystalline, magnetoelastic and magnetostatic contributions into account. These promising results on the epitaxial growth of hybrid piezoelectric/magnetostrictive crystalline system constitute an important step towards the control of magnetization via electrically generated static and/or dynamic strains, and towards the development of magnetic sensors based on surface acoustic wave devices.

The electronic structure of (1 1 1) Sm 1-x Gd x Al 2 , a zero-magnetization ferromagnet, is investigated by angle- and spin- resolved photoemission spectroscopy. An intense electron pocket strongly localized around [Formula: see text] and close to the Fermi level is observed and analyzed in detail. Its various characteristics, combined with electronic structure calculations, reveal a resonant surface state of 5d character and Λ 1 symmetry, likely built on bulk states developing around L points. It exhibits moreover a low temperature positive spin polarization at the Fermi level, of strong interest for spin-dependent transport properties in Sm 1-x Gd x Al 2 -based spintronic devices.

Organic multiferroic tunnel junctions based on La 0.6 Sr 0.4 MnO 3 /poly(vinylidene fluoride) (PVDF)/Co structures are fabricated. The tunneling magneto-resistance sign can be changed by electrically switching the ferroelectric polarization of PVDF barrier. It is demonstrated that the spin-polarization of the PVDF/Co spinterface can be actively controlled by tuning the ferroelectric polarization of PVDF. This study opens new functionality in controlling the injection of spin polarization into organic materials via the ferroelectric polarization of the barrier., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report on magnetic and magnetoelastic measurements for a 5000 Å (110) SmFe(2) thin film, which was successfully analyzed by means of a point charge model for describing the effect of the epitaxial growth in this kind of system. Some of the main conclusions of the Mössbauer and magnetoelastic results and the new magnetization results up to 5 T allow us to get a full description of the crystal electric field, exchange, and magnetoelastic behavior in this compound. So, new single-ion parameters are obtained for the crystal field interaction of samarium ions, A(4)(r(4)) = +755 K/ion and A(6)(r(6)) = -180 K/ion, and new single-ion magnetoelastic coupling B(γ,2) is approximately equal -200 MPa and B(ε,2) is approximately equal MPa, which represent the tetragonal and the in-plane shear deformations, respectively. Moreover, the new thermal behavior of the samarium magnetic moment, the exchange coupling parameter, and the magnetocrystalline anisotropy of the iron sublattice are obtained too. From these, the softening of the spin reorientation transition with respect to the bulk case could be accounted for.