Experimental assignment of long-range magnetic communication through Pd & Pt metallophilic contacts.

Record-breaking magnetic exchange interactions have previously been reported for 3d-metal dimers of the form [M(Pt(SAc))(pyNO)] (M = Ni or Co) that are linked in the solid state metallophilic Pt⋯Pt bridges. This contrasts the terminally capped monomers [M(Pt(SAc))(py)], for which neither metallophilic bridges nor magnetic exchange interactions are found. Computational modeling has shown that the magnetic exchange interaction is facilitated by the pseudo-closed shell d⋯d metallophilic interaction between the filled Pt 5d orbitals.

Two-color synchrotron X-ray spectroscopy based on transverse resonance island buckets.

We report on a novel multi-color method of X-ray spectroscopy at a Synchrotron radiation source that uses two simultaneously filled electron orbits in an electron storage ring to generate multiple soft or tender X-ray beams of different wavelength. To establish the second orbit, we use nonlinear beam dynamics in the so called TRIBs-transverse resonance island buckets-mode of the BESSY II storage ring, where a second electron orbit winds around the regular one leading to transversely separated source points. X-ray beams of multiple colors are generated by imaging the individual source points via different pathways through a monochromator.

Field-induced single-ion magnet based on a quasi-octahedral Co(II) complex with mixed sulfur-oxygen coordination environment.

Synthesis and characterization of structure and magnetic properties of the quasi-octahedral complex (pipH)[Co(TDA)] 2HO (I), (pipH = piperazine dication, TDA = thiodiacetic anion) are described. X-ray diffraction studies reveal the first coordination sphere of the Co(II) ion, consisting of two chelating tridentate TDA ligands with a mixed sulfur-oxygen strongly elongated octahedral coordination environment. SQUID magnetometry, frequency-domain Fourier-transform (FD-FT) THz-EPR spectroscopy, and high-level SA-CASSCF/NEVPT2 quantum chemical calculations reveal a strong "easy-plane" type magnetic anisotropy ( ≈ +54 cm) of complex I.

Applying Unconventional Spectroscopies to the Single-Molecule Magnets, Co(PPh ) X (X=Cl, Br, I): Unveiling Magnetic Transitions and Spin-Phonon Coupling.

Large separation of magnetic levels and slow relaxation in metal complexes are desirable properties of single-molecule magnets (SMMs). Spin-phonon coupling (interactions of magnetic levels with phonons) is ubiquitous, leading to magnetic relaxation and loss of memory in SMMs and quantum coherence in qubits. Direct observation of magnetic transitions and spin-phonon coupling in molecules is challenging.

Spectroscopic Investigation of a Metal-Metal-Bonded Fe Single-Molecule Magnet with an Isolated = / Giant-Spin Ground State.

The metal-metal-bonded molecule [BuN][(L)Fe(dmf)] (Fe) was previously shown to possess a thermally isolated spin = / ground state and found to exhibit slow magnetization relaxation below a blocking temperature of ∼5 K [ , , 13949-13956]. Here, we present a comprehensive spectroscopic investigation of this unique single-molecule magnet (SMM), combining ultrawideband field-swept high-field electron paramagnetic resonance (EPR) with frequency-domain Fourier-transform terahertz EPR to accurately quantify the spin Hamiltonian parameters of Fe. Of particular importance is the near absence of a 4th-order axial zero-field splitting term, which is known to arise because of quantum mechanical mixing of spin states on account of the relatively weak spin-spin (superexchange) interactions in traditional polynuclear SMMs such as the celebrated Mn-acetate.

Phonon anharmonicities and ultrafast dynamics in epitaxial SbTe.

In this study we report on the investigation of epitaxially grown SbTe by employing Fourier-Transform transmission Spectroscopy (FTS) with laser-induced Coherent Synchrotron Radiation (CSR) in the Terahertz (THz) spectral range. Static spectra in the range between 20 and 120 cm highlight a peculiar softening of an in-plane IR-active phonon mode upon temperature decrease, as opposed to all Raman active modes which instead show a hardening upon temperature decrease in the same energy range. The phonon mode softening is found to be accompanied by an increase of free carrier concentration.

A Synergy and Struggle of EPR, Magnetometry and NMR: A Case Study of Magnetic Interaction Parameters in a Six-Coordinate Cobalt(II) Complex.

Herein, we combine for the first time SQUID magnetometry, cw-EPR, THz-EPR, and paramagnetic NMR spectroscopies to study the magnetic properties of a high-spin cobalt(II) heteroscorpionate complex. Complementary information provided by these methods allowed precise determination of the magnetic interaction parameters, thereby removing the ambiguity inherit to single-method studies. We systematically investigate the extent to which information about the magnetic interaction parameters can be deduced from reduced data sets.

Advanced Paramagnetic Resonance Studies on Manganese and Iron Corroles with a Formal d Electron Count.

Metallocorroles wherein the metal ion is Mn and formally Fe are studied here using field- and frequency-domain electron paramagnetic resonance techniques. The Mn corrole, Mn(tpfc) (tpfc = 5,10,15-tris(pentafluorophenyl)corrole trianion), exhibits the following = 2 zero-field splitting (zfs) parameters: = -2.67(1) cm, || = 0.

Angular Momentum Flow During Ultrafast Demagnetization of a Ferrimagnet.

One of the key processes setting the speed of the ultrafast magnetization phenomena is the angular momentum transfer from and into the spin system. However, the way the angular momentum flows during ultrafast demagnetization and magnetization switching phenomena remains elusive so far. We report on time-resolved soft x-ray magnetic circular dichroism measurements of the ferrimagnetic GdFeCo alloy allowing us to record the dynamics of elemental spin and orbital moments at the Fe and Gd sites during femtosecond laser-induced demagnetization.

Recent advances in ultrafast X-ray sources.

Over more than a century, X-rays have transformed our understanding of the fundamental structure of matter and have been an indispensable tool for chemistry, physics, biology, materials science and related fields. Recent advances in ultrafast X-ray sources operating in the femtosecond to attosecond regimes have opened an important new frontier in X-ray science. These advances now enable: (i) sensitive probing of structural dynamics in matter on the fundamental timescales of atomic motion, (ii) element-specific probing of electronic structure and charge dynamics on fundamental timescales of electronic motion, and (iii) powerful new approaches for unravelling the coupling between electronic and atomic structural dynamics that underpin the properties and function of matter.

Determination of Large Zero-Field Splitting in High-Spin Co(I) Clathrochelates.

Zero-field splitting (ZFS) of three high-spin Co(I) ( S = 1) clathrochelate complexes was determined by frequency-domain Fourier-transform THz-EPR (FD-FT THz-EPR). The following axial and rhombic ZFS values ( D and E, respectively) were determined: [N( n-Bu)]Co(GmCl)(BPh) (1, D/ hc = +16.43(1) cm, E/ hc = 0.

Ultrafast and Energy-Efficient Quenching of Spin Order: Antiferromagnetism Beats Ferromagnetism.

By comparing femtosecond laser pulse induced ferro- and antiferromagnetic dynamics in one and the same material-metallic dysprosium-we show both to behave fundamentally different. Antiferromagnetic order is considerably faster and much more efficiently reduced by optical excitation than its ferromagnetic counterpart. We assign the fast and extremely efficient process in the antiferromagnet to an interatomic transfer of angular momentum within the spin system.

Analysis of Magnetic Anisotropy and the Role of Magnetic Dilution in Triggering Single-Molecule Magnet (SMM) Behavior in a Family of Co Y Dinuclear Complexes with Easy-Plane Anisotropy.

Three new closely related Co Y complexes of general formula [Co(μ-L)(μ-X)Y(NO ) ] (X =NO 1, benzoate 2, or 9-anthracenecarboxylato 3) have been prepared with the compartmental ligand N,N',N''-trimethyl-N,N''-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H L). In these complexes, Co and Y are triply bridged by two phenoxide groups belonging to the di-deprotonated ligand (L ) and one ancillary anion X . The change of the ancillary bridging group connecting Co and Y ions induces small differences in the trigonally distorted CoN O coordination sphere with a concomitant tuning of the magnetic anisotropy and intermolecular interactions.

Recent progress in synchrotron-based frequency-domain Fourier-transform THz-EPR.

We describe frequency-domain Fourier-transform THz-EPR as a method to assign spin-coupling parameters of high-spin (S>1/2) systems with very large zero-field splittings. The instrumental foundations of synchrotron-based FD-FT THz-EPR are presented, alongside with a discussion of frequency-domain EPR simulation routines. The capabilities of this approach is demonstrated for selected mono- and multinuclear HS systems.

Analysis of granular packing structure by scattering of THz radiation.

Scattering methods are widely used to characterize the structure and constituents of matter on small length scales. This motivates this introductory text on identifying prospective approaches to scattering-based methods for granular media. A survey to light scattering by particles and particle ensembles is given.

Spectroscopic and Computational Studies of Spin States of Iron(IV) Nitrido and Imido Complexes.

High-oxidation-state metal complexes with multiply bonded ligands are of great interest for both their reactivity as well as their fundamental bonding properties. This paper reports a combined spectroscopic and theoretical investigation into the effect of the apical multiply bonded ligand on the spin-state preferences of threefold symmetric iron(IV) complexes with tris(carbene) donor ligands. Specifically, singlet (S = 0) nitrido [{PhB(Im)}FeN], R = Bu (1), Mes (mesityl, 2) and the related triplet (S = 1) imido complexes, [{PhB(Im)}Fe(NR')], R = Mes, R' = 1-adamantyl (3), Bu (4), were investigated by electronic absorption and Mössbauer effect spectroscopies.

Versatile soft X-ray-optical cross-correlator for ultrafast applications.

We present an X-ray-optical cross-correlator for the soft ([Formula: see text]) up to the hard X-ray regime based on a molybdenum-silicon superlattice. The cross-correlation is done by probing intensity and position changes of superlattice Bragg peaks caused by photoexcitation of coherent phonons. This approach is applicable for a wide range of X-ray photon energies as well as for a broad range of excitation wavelengths and requires no external fields or changes of temperature.

Multifaceted magnetization dynamics in the mononuclear complex [ReCl(CN)].

The mononuclear complex (BuN)[ReCl(CN)]·2DMA (DMA = N,N-dimethylacetamide) displays intricate magnetization dynamics, implying Orbach, direct, and Raman-type relaxation processes. The Orbach relaxation process is characterized by an energy barrier of 39 K (27 cm) that is discussed based on high-field electron paramagnetic resonance (EPR), inelastic neutron scattering and frequency-domain THz EPR investigations.

Laser-pump/X-ray-probe experiments with electrons ejected from a Cu(111) target: space-charge acceleration.

A comprehensive investigation of the emission characteristics for electrons induced by X-rays of a few hundred eV at grazing-incidence angles on an atomically clean Cu(111) sample during laser excitation is presented. Electron energy spectra due to intense infrared laser irradiation are investigated at the BESSY II slicing facility. Furthermore, the influence of the corresponding high degree of target excitation (high peak current of photoemission) on the properties of Auger and photoelectrons liberated by a probe X-ray beam is investigated in time-resolved pump and probe measurements.

Far-Infrared and Raman Spectroscopy Investigation of Phonon Modes in Amorphous and Crystalline Epitaxial GeTe-Sb2Te3 Alloys.

A combination of far-infrared and Raman spectroscopy is employed to investigate vibrational modes and the carrier behavior in amorphous and crystalline ordered GeTe-Sb2Te3 alloys (GST) epitaxially grown on Si(111). The infrared active GST mode is not observed in the Raman spectra and vice versa, indication of the fact that inversion symmetry is preserved in the metastable cubic phase in accordance with the Fm3 space group. For the trigonal phase, instead, a partial symmetry break due to Ge/Sb mixed anion layers is observed.

Analysis of the halo background in femtosecond slicing experiments.

The slicing facility FemtoSpeX at BESSY II offers unique opportunities to study photo-induced dynamics on femtosecond time scales by means of X-ray magnetic circular dichroism, resonant and non-resonant X-ray diffraction, and X-ray absorption spectroscopy experiments in the soft X-ray regime. Besides femtosecond X-ray pulses, slicing sources inherently also produce a so-called `halo' background with a different time structure, polarization and pointing. Here a detailed experimental characterization of the halo radiation is presented, and a method is demonstrated for its correct and unambiguous removal from femtosecond time-resolved data using a special laser triggering scheme as well as analytical models.

Cyanide Single-Molecule Magnets Exhibiting Solvent Dependent Reversible "On" and "Off" Exchange Bias Behavior.

The syntheses, structures, and magnetic properties of four new complex salts, (PPN){[Mn(III)(salphen)(MeOH)]2[M(III)(CN)6]}·7MeOH (Mn2M·7MeOH) (M = Fe, Ru, Os and Co; PPN(+) = bis(triphenylphosphoranylidene)ammonium cation; H2salphen = N,N'-bis(salicylidene)-1,2-diaminobenzene), and a mixed metal Co/Os analogue (PPN){[Mn(III)(salphen)(MeOH)]2[Co(III)0.92Os(III)0.08(CN)6]}·7MeOH were undertaken.