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International audience; Irradiation of the heterostructure glass/Ta/Pt/GdFeCo/IrMn/Pt by 50 fs ultra-short laser pulses causes local thinning of the film down to~12-30 nm depth. These pits are distinguished by Atomic Force Microscopy (AFM), while their stray magnetic fields were detected by Magnetic Force Microscopy (MFM). The crater was formed due to layer-by-layer evaporation of the material. No sign of melting was found in the vicinity of the crater at subthreshold laser fluence below 12-15 mJ/cm 2 , but exceeding of the threshold caused destruction of the layers. Energy-dispersive X-ray spectroscopy (EDX) revealed depletion of Gd, Fe and Co, responsible for magnetic properties of the subthreshold crater. The amplitude of the local MOKE signal decreased down to 1.7 times in the irradiated area, while thinning of the ferromagnetic layer was 1.1 times. No proportional change of magneti-zation was caused by bias effect of IrMn layer. Decreased elastic modulus was found inside the subthreshold crater in the irradiated areas. Laser engineering of the surface of GdFeCo thin films opens the way for local control of energy balance between magnetic anisotropy, exchange coupling and Zeeman energy and creation of separated sectors for capture, storage and analysis of the ferromagnetic nanoparticles.

New method for the synthesis of the mononuclear anionic iron dinitrosyl complexes (DNICs) as prospective agents for nitric oxide (NO) chemotherapy of oncological diseases has been developed. Mononuclear anionic DNIC of the composition (N2H5)+[Fe(SR)2(NO)2]- with R = 5-nitropyridinyl (I) has been synthesized by the reaction of aqueous solutions of Na2[Fе(S2O3)2(NO)2] and N2H5[SС5H3N2O2] salts. The latter one was synthesized by the reduction of bis-(5-nitro-pyridin-2-yl) disulfide with hydrazine hydrate in ethanol at T = 25 °C. Physical-chemical properties of the synthesized complex were studied by X-ray, SEM, IR-, EPR, Mossbauer spectroscopy and SQUID magnetometry in combination with DFT quantum-chemical calculation of molecular structure and spectroscopic properties. Complex I was found to generate NO in proton media without additional activation. The cytotoxicity of I to human tumor cells of various geneses, viz. ovarian cancer SKOV3, colon cancer LS174T and non-small cell lung cancer A549 was discovered for the first time.

Effect of cell microbeads labelled with commercial α-Fe2O3 nanoparticles (NPs) on magnetic properties of MgO/CoFeB/Ta/CoFeB/MgO/GaAs spin valves and monolayer system MgO/CoFeB/MgO/GaAs was observed. Magnetic scattering field of α-Fe2O3 microbeads shifts critical magnetic field (CMF) of magnetization switching of free layer in spin valves. The CMF is controlled by energy balance of magnetic anisotropy, interlayer exchange coupling, Zeeman energy and scattering magnetic field of microbeads. Local magnetic field of microbeads and their effect on CMF were estimated accordingly with the magnetic profile of the surface scanned by magnetic force microscope. Magnetic instability of film magnetization caused by magnetic microbeads deposited on the spin valve surface was revealed.

There is a variety of transition metal and lanthanide complexes, which exhibit properties typical of Single Ion Magnets (SIMs) only in the presence of external DC magnetic field (the so-called field induced SIMs). Here we propose composite material, in which powder sample of field induced SIM based on the recently reported hexacoordinated Co(II) complex is mixed with ferromagnetic microparticles (MPs). Controllable residual magnetic field of MPs acts as internal magnetic field suppressing quantum tunneling of magnetization and making it possible to observe slow magnetic relaxation in the cobalt complex even in the absence of external magnetic field.

International audience; Magnetic configurations in synthetic ferrimagnet CoFeB/Ta/CoFeB bilayer with strong perpendicular ani-sotropy have been systematically studied. Magnetization versus field hysteresis loop has been measured for different temperature ranging from 5 to 300 K. The applied field – temperature (H-T) magnetization switching diagram has been constructed by extracting the different switching fields as a function of temperature. This switching diagram can be well explained by considering the competition between energy barrier of layer's magnetization reversal, interlayer exchange coupling, and Zeeman energy.

International audience; Magnetic configurations in Pt/Co/Ir/Co/Pt synthetic ferrimagnet bilayer of strong perpendicular anisotropy have been systematically studied. Magnetization versus field hysteresis loops have been measured for different temperatures ranging from 5 to 300 K. The applied field e temperature (H-T) magnetization switching diagram has been constructed by extracting the different switching fields as a function of temperature. This switching diagram can be well explained by considering the competition between energy barrier of layer's magnetization reversal, interlayer exchange coupling, and Zeeman energy.

The concentration effect of charge carriers on the magnetic moment of ferromagnetic MnSb nanoclusters embedded in GaSbMn thin films is reported. High concentration of holes enhances the probability of their tunneling through the barrier between the semiconductor matrix and the MnSb nanocluster. Enrichment of the MnSb clusters by Mn2+ ions instead of Mn3+ enhances their ferromagnetism. Dynamics of magnetization relaxation of the MnSb clusters under applied magnetic field has been studied in the 8–300 K temperature range. Magnetic anisotropy constant ∼3.2·104 erg/cm3 has been determined. The fluctuation field HF = 7 Oe and the activation volume VA = 1.7·10−16 cm3 have been extracted from magnetic viscosity data.

The Si:B micro-crystals enriched with 29 Si isotope have been studied by high resolution nuclear magnetic resonance (NMR) in the 300–800 K temperature range. The recovery of nuclear magnetization saturated by radiofrequency impulses follows pure power-law kinetics at 300 K, while admixture of exponential relaxation takes place at 500 K. The power-law relaxation corresponds to direct electron–nuclear relaxation due to the inhomogeneous distribution of paramagnetic centers, while exponential kinetics corresponds to the nuclear spin diffusion mechanism. The inhomogeneous distribution of deformation defects is a most probable reason of the power-law kinetics of nuclear spin relaxation.

Nanostructured powders of terbium oxides were prepared by the thermal decomposition of terbium acetate at different temperatures. The powders were investigated by means of XRD, HRTEM, magnetic measurements, and IR spectroscopy. It has been found that the most likely composition of the oxides is Tb4O7, and the powders containing more than one crystalline phase. At low temperatures the prepared oxides exhibit antiferromagnetic ordering with the Weiss constants ranging from −14 to −22 K. At 2 K the effective value of total angular momentum per one Tb ion in the paramagnetic state J = 2.5 ± 0.1. The effects of the calcination temperature on the crystal structure, microstructure and magnetic behaviors of the samples are discussed in terms of that surface impurities presented in the nanocrystalline powders of Tb oxides influence the cation Tb4+/Tb3+ ratio in their crystal lattice.

The reaction of the neutral [Mn(salpn)C(CN)3(H2O)] (salpn2 − = N,N′-1,3-propylenebis(salicylideneiminato) dianion) with [FeIII(CN)6]3 − in the presence of strong oxidizer (NH4)2S2O8 yields a binuclear anion complex [NH3CH2CH2CH2NH3]2 +{[MnIII(salpn)(H2O)][FeIII(CN)6]}2 − (1). Its structure, DC and AC susceptibility have been studied. Frequency dependence of the AC susceptibility characteristic for single-molecule magnets has been found.

Triclinic and monoclinic polymorph modifications of the complex [Co(qu)2Br2] were obtained, and its molecular and crystal structures were determined by single crystal X-ray analysis. The magnetic anisotropy parameter D and g-tensor were estimated by SQUID measurements and ab initio (SA-CASSCF/NEVPT2) quantum-chemical calculations. The ligand field effect and magnetostructural correlations in the family of complexes [Co(qu)2X2] (qu = quinoline and X = NCS−, Cl−, Br− and I−) were analyzed. A correlation between the ligand field and the energies of the molecule excited states was revealed.

In Pt/Co/Ir/Co/Pt synthetic ferrimagnet, non-monotonic magnetic relaxation (NMMR) caused by switching of external magnetic dependends on Co layer thicknesse and temperature. In this paper, we have varied thickness of one of the Co layers in the Pt/Co/Ir/Co/Pt synthetic ferrimagnet in the 0.6–1.0 nm range at fixed Co layer thickness of another layer 1.1 nm in the 50–300 K range to find experimental conditions for NMMR. We found interdependence between Co layer thickness tCo and temperature T providing NMMR. Energy balance between magnetic anisotropies and exchange interaction of the two Co layers stipulates linear dependence of nessecary T on tCo. Exsact expression limitating magnetic anisotropies of the thick and thin Co layers and predicting NMMR conditions in tCo - T space is proposed. Altough all mentioned results relates to experiments in permanent magnetic field, the contribution of the NMMR to the magnetic hysteresis loops recorded in sweeping magetic field was experimentally found. Obtained results can be used for wide family of synthetic ferrimagnets with perpendicular anisotropy.

The α-Fe core/PrDy-FeCo-B(48 at.%)α-Fe(52 at.%) shell and GdPrDy(FeCo)B microwires were grown by pendant drop melt (PDM) extraction technique. Single core–shell microwires of ~80–100 μm diameter and 2–20 mm length manifest rectangular hysteresis loops corresponding to ~100 Oe switching magnetic fields. Bistability of the microwires relates to single domain state of the α-Fe inner core revealed by scanning electron microscopy (SEM). Rare-earth amorphous PrDy-FeCo-B shell of the microwire scanned by magnetic force microscope (MFM) possesses magnetization reversal nuclei corresponding to the α-Fe inclusions. Interwire magnetic dipole interaction and scattering of microwire size change shape of the magnetic hysteresis loop and increase coercive field up to 983 Oe, in chaotic ensembles of the core–shell microwires. The GdPrDy(FeCo)B microwires of the same sizes with no Fe core possess “butterfly” type of the hysteresis loop of high coercivity ~20 kOe.

Ordered arrays of nanowires of pure SpFeMn(C 2 O 4 ) 3 collinear antiferromagnet have been synthesized in pores of anodized aluminum oxide (AAO) 20 nm and 200 nm in diameter. It was found that the growth of spin-canted phase presented in the bulk samples is suppressed in nanowires. The decrease in the nanowires diameter results in magneto-crystalline anisotropy increase.

Electrochemical oxidation of donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) in 1,1,2-trichloroethane-ethanol in the presence of electrolytes including two type of ligands, namely, (Ph4P)2[M(dca)2(SCN)2], M = Mn, Ni; dca = [N(CN)2]−, has been performed and analyzed for the first time. It has been found that in the reaction of electrochemical oxidation of BEDT-TTF, [M(dca)2(SCN)2]2− anion decomposes to form new metal-complex anions, [Mn(dca)3(SCN)2·H2O]3− and [Mn(SCN)6]4− or [Ni(SCN)6]4−, respectively, as well as (dca) and SCN anions. New radical cation salts, (BEDT-TTF)4Mn[(dca)3(SCN)2·H2O](SCN)x, x

Two bifunctional supramolecular systems [RuNO(NH 3 ) 4 OH] 2+ · [RuNO(NH 3 ) 4 H 2 O] 3+ Cd 3+ (H 2 O) 6 · 2[TCAS] 4- · 4H 2 O (1) and [RuNO(NH 3 )4OH] 2+ · [RuNO(NH 3 ) 4 H 2 O] 3+ · Dy 3+ (H 2 O) 6 · 2[TCAS] 4- · 4H 2 O (2) on the platform of p-sulfonatothiacalix[4]arene containing photochromic mononitrosyl Ru and paramagnetic rare-earth (Cd 3+ , Dy 3+ ) cations have been synthesized. The crystal structures of 1 and 2 are discussed. Their photochromic, magnetic and photomagnetic properties studied by IR and SQUID experimental techniques are presented.

The analysis of temperature dependences of magnetic moment of several new iron nitrosyl complexes in solid phase allowed the value of exchange interaction (J) between two iron ions to be estimated in each type complexes and a systematic decrease of J together with the increase in the ESR linewidth with a distance between iron ions to be observed. It was found that exchange interaction in the complexes involves two components, namely, direct exchange interaction and indirect one transferred through organic ligands.

The effect of UV light on Weiss temperature and ESR spectra in 1-isopropyl-3, 3, 5', 6'-tetramethylspiro[indolin-2,2'-[2H]pyrano[3,2-b]pyridinium] tris(oxalato)chromate (III) (Sp{sub 3}Cr(C{sub 2}O{sub 4}){sub 3}) has been found. Additional line has been observed in the ESR spectra of irradiated samples in 'strong' magnetic fields of {approx}15 kOe. The analysis of angular dependences of the ESR spectra allowed a contribution of Cr{sup 3+} ions to magnetic properties of Sp{sub 3}Cr(C{sub 2}O{sub 4}){sub 3} to be determined. The zero-field splitting parameters D=0.619 cm{sup -1}, E=0.024 cm{sup -1} were derived from the experimental data. The parameters were typical for Cr{sup 3+} in the chromium oxalate. Weiss temperature changed sign from 25 to -25 K under UV irradiation. The value of Weiss temperature and its changing cannot be explained by exchange interaction, dipole-dipole interaction or the effect of crystal field. The existence of Weiss temperature is explained by the changes in amount and spin of paramagnetic particles. The change is due to thermoactivated redistribution of electrons between chromium ions and spiropyrane molecules. Light-induced transfer of electrons is also explaining the change in sign of Weiss temperature under UV irradiation. - Graphical abstract: Fragment of crystal structure of (Sp{sub 3}Cr(C{sub 2}O{sub 4}){sub 3}). Temperature dependences of reciprocalmore » molar magnetic moment of the sample at T=2 K: (1) before irradiation, and (2) after UV irradiation.« less

The crystals of new bifunctional molecular metals based on bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) radical cation salts with paramagnetic [M(CN) 6 ] 3− anions, where M = Fe, Cr, (Fe 0.5 Co 0.5 ), and a diamagnetic [Co(CN) 6 ] 3− anion of general formula: β″-(BEDO-TTF) 6 A x [M(CN) 6 ]·G 2− x , where G is a guest solvent molecule (acetonitrile or dimethylformamide); A = H 3 O + , K + ; x ∼ 0.5, were synthesized by electrocrystallization. Conductivity measurements show metallic behavior for all these salts down to a temperature of 4.2 K. The effect of the BEDO-TTF intracrystalline field on the magnetic properties of the [Fe(CN) 6 ] 3− complex anion was observed. Random distribution of these complexes along BEDO-TTF layers modulates the local crystalline environment of these anions and splitting of their Zeeman sublevels. Powder-like EPR spectrum of [Fe(CN) 6 ] 3− anions in these crystals corresponds to this space disorder. The intracrystalline field of the BEDO-TTF layers strongly changes the temperature dependence of effective magnetic moment of the [Fe(CN) 6 ] 3− anion in comparison with the K 3 Fe(CN) 6 . This fact indicates redistribution of spin density inside complexes and changes in their effective spin value under the action of the BEDO-TTF environment.

Electron spin resonance (ESR) is measured in arrays of Ge 0.99 Mn 0.01 nanowires (NWs). We show that the ESR spectrum comprises four lines corresponding to the different magnetic subsystems. Two lines are attributed to spin-wave excitations in the Mn +3 ion subsystem. The third component corresponds to the resonance in the Mn +2 ions. The last component has an asymmetric Dyson form and characterizes the resonance in the mobile paramagnetic centers. We demonstrate that temperature dependences of ESR parameters are correlated in subsystems of the localized magnetic centers (Mn +3 and Mn +2 ions) and delocalized band carriers. It implies the presence of exchange interactions between the localized Mn ions and spin-polarized carriers.

Silicon oxidation by oxygen depends on the magnetic field and exhibits isotope effect: silicon atoms 29 Si with magnetic nuclei are oxidized twice as fast as atoms 28 Si and 30 Si with nonmagnetic nuclei. Both effects certify that the oxidation is a spin selective reaction in which radical pairs participate. The dominating oxidizing species are oxygen molecules in triplet spin state which generate triplet radical pairs. Zeeman interaction and hyperfine coupling with 29 Si nuclei in these pairs stimulate triplet–singlet spin conversion and transform triplet pairs into the reactive singlet ones. The subsequent spin allowed reactions in the latter result in the oxidation products.

In α′-(BEDT-TTF) 2 IBr 2 single crystals at high temperatures (above 210 K) we observed anisotropic single Lorenz line with constant integral amplitude obeying Pauli rule for charge carriers in metals. Charge ordering at 208 K was accompanied by features on the temperature dependencies of the EPR parameters: integral intensity (magnetic susceptibility), g -factor and linewidth Δ H . This fact corresponds to spin transition in the subsystem of the delocalized–localized charge carriers. Exchange interaction between localized charge carriers provides rapid decrease of magnetic susceptibility below 50 K.

The purpose of the work is to investigate relaxation of residual stresses and metastable point defects and plastic properties of ionic crystals in crossed static and microwave magnetic fields at the paramagnetic resonance condition. It is revealed that coincidence of quantum energy of a microwave field with energy of Zeeman splitting of electronic spin sublevels of paramagnetic centers leads to an increase in relaxation rate of residual stresses and of metastable point defects, and, as a result, to resonant weakening of crystals which manifests itself in an increase of dislocation mobility and macroplastic flow rate, as well as in a decrease of crystal microhardness. It is shown that the metastable Ca and Eu aggregates sensitive to a static magnetic field in the absence of microwave fields are responsible for resonant weakening. The resonance arises in short-lived non-thermalized states of these aggregates excited by thermal fluctuations.

Electron spin resonance (ESR) is measured in arrays of Ge nanowires (NWs) doped with Mn, x =1% and 3%. Contributions due to localized magnetic ions and charge carriers to the magnetic properties of NWs are observed. Doping with Mn causes a ferromagnetic ordering at temperatures up to 285 K. Zero-field ferromagnetic resonance (FMR) is observed in Ge 0.97 Mn 0.03 NWs at room temperature. We demonstrate the influence of the Mn concentration on the angular dependence and linewidth of the FMR spectra. We found a remarkable correlation between parameters of the FMR on Mn ions and the paramagnetic resonance on spin-polarized carriers.

The reaction of the [Mn12O12(O2CCHCl2)16(H2O)4] cluster with tetrathiotetracene triiodide has been studied and, for the first time, reduction fragmentation of Mn12 cluster to Mn6 cluster has been found.