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A series of magnetization reversal curves of the chiral molecular magnet K0.4[Cr(CN)6][Mn(R/S)-pn](R/S)-pnH0.6 was measured and analyzed, which allowed the detection of maxima in the sample reversal diagram (First Order Reversal Curves, FORC). These maxima correspond to the contributions of domain walls and spin solitons. It was found that an increase in temperature from 2 K to 20 K leads to an increase in the interval between the maxima along the axis of the interaction fields and to the dominance of the contribution of the domain walls over the spin solitons to the magnetization reversal of the sample. It has been established that the magnetization reversal diagram depends on the relaxation of the magnetic moment of the samples in a constant field.

Periodical transformation of ferroin to ferriin is accompanied by changes in magnetic properties of liquids during Belousov&ndash, Zhabotinsky (BZ) reaction malonic acid, sodium bromide, sodium bromate, ferroin, and sulfuric acid. Instead of the earlier studied oscillation of microwave conductivity accompanying an oscillating reaction, we propose a flash technique to interrupt the BZ reaction by rapid freezing. Rapid cooling of a solution during chemical oscillations results in a frozen system with a fixed concentration of paramagnetic centers Fe3+. EPR spectrum recorded at different stages of the interrupted reaction corresponds to the exact concentration of the ferroin and ferriin components. Following unfreezing unblocks the BZ reaction, and oscillations are still observed. A simulated spectrum allows one to distinguish two groups of Fe3+ ions of different symmetries. The obtained results are important to explain the earlier observed effect of inhomogeneous magnetic field on BZ reaction front velocity.

Herein, we report the synthesis and magnetic properties of the Co(II) coordination compound with the 1,1′-bis(1-((pyrid-2-ylmethylene)hydrazono)ethyl)ferrocene (L) ligand, having the general formula [CoLCl2]. The static magnetic data analysis supported by the CASSCF/NEVPT2 calculations revealed the presence of the triaxial magnetic anisotropy with Dexp = +35.2 cm−1 and large rhombicity (E/D = 0.31) in this complex (Dcalc = +34.5 cm−1, E/Dcalc = 0.30). The dynamic magnetic data confirm that the complex shows a slow field-induced (HDC = 1000 Oe) magnetic relaxation behaviour.

Magnetocaloric effect (MCE) in an antiferromagnetic holmium (Ho) film is studied near the spin reorientation temperatures. A series of magnetization isotherms from 60 to 150 K around the N\'eel temperature, ${T}_{N}\ensuremath{\approx}130\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ were recorded for both in-plane and out-of-plane magnetic field orientations. A change in entropy, $\mathrm{\ensuremath{\Delta}}{S}_{M}$ of $\text{--}5\phantom{\rule{0.28em}{0ex}}\mathrm{J}/\mathrm{kg}\mathrm{K}$ was found near ${T}_{N}$ for an in-plane field orientation. A large change in $\mathrm{\ensuremath{\Delta}}{S}_{M}$ of \ensuremath{-}11.8 J/kg K due to a fan-helix spin transition at $T=90\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ is observed for an in-plane field orientation. Spin transition at both ${T}_{N}$ and at the fan-helix transition exhibit larger MCE in the in-plane field orientations in comparison with the perpendicular orientation. The value of the refrigerant capacity extracted from the temperature dependence of $\mathrm{\ensuremath{\Delta}}{S}_{M}(T)$ is found to be larger for the ``in- plane'' orientation by a factor of two.

Fe/Fe3O4 nanoparticles have been deposited on the surfaces of ultrathin CoFeB film and CoFeB/Ta/CoFeB hetero-structure to be detected due to the stray field generated by one particle or a cluster of particles. Exchange biased Fe/Fe3O4 core-shell nanoparticles have been used to stabilize the particles magnetization. Comparison between the Atomic Force and Magnetic Force Microscope images and subtraction of corresponding phase contrasts allows visualization of the film magnetization affected by the particles. Spectra of Ferromagnetic Resonance of the ultrathin films with deposited particles allow one to estimate particle/film dipolar interaction. The results will be useful for the development of lab-on-chip sensors of magnetically labeled cells. Estimation of particles number by magnetic response of the CoFeB heterostructure is demonstrated.

Homogeneous composites based on poly(methyl methacrylate) and its copolymers with methacrylic acid and on the nitrosyl iron complexes with 2-mercaptobenzimidazole and 2-mercaptobenzthiazole were synthesized. An analysis of the experimental data obtained by the methods of small-angle X-ray diffraction and SQUID magnetometry in combination with the results of quantum chemical calculations showed that the nitrosyl complexes did not retain their initial binuclear structure under the matrix isolation conditions: some complexes decompose to mononuclear ones. The percentage ratio of the dimers and monomers depends on the fraction of the methacrylic acid copolymer in the polymeric matrix and is almost independent of the type of thiol ligand in the iron complex.

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.

The main parameters of the domain structure of a (PrDy)(FeCo)B sintered permanent magnet are determined using magnetic force microscopy analysis of the magnetic-gradient distribution near the magnet surface. It is shown that the domain wall energy and width are not sensitive to the replacement of Nd with Pr and Dy in the studied RE-TM-B alloy. The anisotropy and exchange interaction constants are obtained. Two competitive processes of magnetization reversal (pinning and nucleation) are defined in sintered permanent magnets (PrDy)(FeCo)B.

The time dependences of the transfer of the magnetic moment between stable magnetic states of heterostructures with two Pt/Co/Ir/Co/Pt ferromagnetic layers with the perpendicular magnetization have been studied. Spontaneous oscillations of the macroscopic magnetization with a period of several hours are observed after switching the magnetic field to a new value. The phase portrait of the magnetic relaxation corresponds to damped oscillations. The macrospin oscillation may be due to the high nucleation rate of the reverse magnetization phase induced by the exchange and magnetic dipole interaction between the phase nucleation centers, which arise in different layers. The changes in the Zeeman energy of the system under magnetic oscillations are considered.

The effect of annealing of a (Pr0.41Ce0.12Dy0.47)13.46(Fe0.64Co0.36)80.3B6.24 alloy at 1000°C on its microstructure and the properties of sintered magnets made of it has been studied. In the annealed state, the composition of the main magnetic phase (Pr,Dy)2(Fe,Co)14B changes sharply (dysprosium content changes), the residual induction of the sintered magnets made of the annealed alloy increases by 6%, and the coercive force determined from magnetization increases by 8.5%. The volume content of the main magnetic phase R2(Fe,Co)14B in sintered magnets (Nb,Dy)–(Fe,Co)–B and (Pr,Dy)–(Fe,Co)–B is found. The content of this phase in neodymium-based magnets is approximately half as much.

Isostructural mononuclear complexes of heavy lanthanides with the pentadentate Schiff-base dapsc ligand were synthesized, [Ln(H2dapsc)(H2O)4](NO3)3 (Ln = Tb, Dy, Ho, Er), and characterized structurally and magnetically. AC magnetic susceptibility measurements revealed that complexes of Dy3+ and Er3+ Kramers ions are field-induced single-ion magnets whereas the Tb and Ho complexes show no slow magnetic relation in DC fields up to 6000 Oe. DC and AC magnetic properties of these complexes were rationalized in terms of superposition crystal-field model calculations for Ln3+ ions, which have resulted in good agreement between the experiment and the theory. It is shown that low single-molecule magnet characteristics of the Dy and Er complexes and the absence of slow-magnetic relaxation in the Tb and Ho complexes are primarily due to the low-symmetry coordination of Ln3+ ions.

A set of partially uncoupled NiFe/Cu/IrMn exchange biased thin films with variable thickness of non-magnetic Cu spacer is characterized by ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) techniques applied complementary to reveal time-scale dependent effects of uncoupling between ferromagnetic and antiferromagnetic layers on high-frequency magnetization dynamics. The results correlate with interfacial grain texture variations and static magnetization behavior. Two types of crystalline phases with correlated microwave response are revealed at the ferro–antiferromagnet interface in NiFe/Cu/IrMn thin films. The 1st phase forms well-textured NiFe/IrMn grains with NiFe (111)/IrMn (111) interface. The 2nd phase consists of amorphous NiFe/IrMn grains. Intercalation of NiFe/IrMn by Cu clusters results in relaxation of tensile strains at the NiFe/IrMn interface leading to larger size of grains in both the NiFe and IrMn layers. The contributions of well-textured and amorphous grains to the high-frequency magnetization reversal behavior are distinguished by FMR and BLS techniques. Generation of a spin-wave mode is revealed in the well-textured phase, whereas microwave response of the amorphous phase is found to originate from magnetization rotation dominated by a rotatable magnetic anisotropy term. Under fixed FMR frequency, the increase of Cu thickness results in higher magnetization rotation frequencies in the amorphous grains.

Spontaneous demagnetization jumps are observed in sintered magnets (Nd0.6Dy0.4)16(Fe0.77Co0.23)78B6 in a constant magnetic field after a sharp decrease in an external magnetic field from the value corresponding to the saturation to a value close to the coercive force. It is shown that the number of the magnetization jumps is proportional to their amplitudes. A low value of the autocorrelation coefficient between the jump amplitude and the time of its appearance (R < 0.1) demonstrate the stochasticity of the jumps. It is found that the spectral jump density is independent of the frequency, i.e., a white magnetic noise is observed. The distribution of the magnetic field gradient has been obtained near the sample surface that makes it possible to distinguish domains and the grain magnetization in the dependence on the direction of the texturing of the sintered magnet.

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.

Negative magnetoresistance modifying the quality factor of a microwave cavity under the magnetization switching of ferromagnetic layers has been discovered in a MgO/CoFeB/MgO/Ta film with a single ferromagnetic layer and a MgO/CoFeB/Ta/CoFeB/MgO/Ta spin valve consisting of two ferromagnetic CoFeB layers. The dependence of the first derivative dP/dH of the microwave absorption signal on the dc magnetic field of the spectrometer exactly reproduce the magnetic hysteresis loops of the sample. The slope of these dependences and the amplitude of dP/dH jumps under remagnetization of the layers are determined by the interplay of a negative magnetoresistance of individual layers and a positive giant magnetoresistance of the entire multilayer structure. The discovered phenomenon allows using microwave absorption for making a high-sensitivity contact-free indicator of the basic magnetization states of a spin valve.

Magnetic jumps with the amplitudes of 0.01%–0.1% of the saturation magnetization were observed during the magnetization reversal of a [Mn(II)(HL)(H2O)][Mn(III)(CN)6]·2H2O molecular ferrimagnet. Fourier transform of the time series of the magnetization jumps showed that its frequency spectrum is close to that of white noise. The distribution of the jump amplitudes versus time revealed that large jumps dominate at the onset of magnetization reversal.

Magnetic properties of powder (Pr,Dy)FeCoB ferrimagnetic alloys and effects of annealing, surface states were analyzed. X-ray photoelectron spectroscopy and Mössbauer spectra of powders indicate the effect of surface states on phase composition and magnetic properties of the studied powder, if particles average size is smaller than 10 μm. Effect of stoichiometry on magnetic anisotropy was found. Thermal stability of anisotropy field was proved by replacement of Fe atoms with Co atoms.

The dependence between the coercive force and the average hysteresis loop record time was revealed in sintered (Pr1 – x Dy x )13(Fe1 – y Co y )79B8 magnets. The coercive force was established to grow by 22% with an increase in the average hysteresis loop sweep rate within a range of 1.1 × 102–3 × 105 Oe/min, obeying a logarithmic dependence on the loop passage velocity with saturation at low rates. Some domain structure transformations produced by a magnetic field in the process of magnetization were established by magnetic force microscopy.

Two one-dimensional cyano-bridged coordination polymers, namely, {[MnII(dapsc)][MnIII(CN)6][K(H2O)2.75(MeOH)0.5]}n·0.5n(H2O) (I) and {[MnII(dapsc)][MnIII(CN)6][K(H2O)2(MeOH)2]}n (II), based on alternating high-spin MnII(dapsc) (dapsc = 2,6-diacetylpyridine bis(semicarbazone)) complexes and low-spin orbitally degenerate hexacyanomanganate(III) complexes were synthesized and characterized structurally and magnetically. Static and dynamic magnetic measurements reveal a single-chain magnet (SCM) behavior of I with an energy barrier of Ueff ≈ 40 K. Magnetic properties of I are analyzed in detail in terms of a microscopic theory. It is shown that compound I refers to a peculiar case of SCM that does not fall into the usual Ising and Heisenberg limits due to unconventional character of the MnIII-CN-MnII spin coupling resulting from a nonmagnetic singlet ground state of orbitally degenerate complexes [MnIII(CN)6]3-. The prospects of [MnIII(CN)6]3- complex as magnetically anisotropic molecular building block for engineering molecular magnets are critically analyzed.

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.

We report a combined experimental characterization and theoretical modeling of the hexa-coordinated high-spin Co(ii) complex cis-[Co(hfac)2(H2O)2] (I). The magnetic static field (DC) data and EPR spectra (measurements were carried out on the powder samples of diluted samples cis-[Co0.02Zn0.98 (hfac)2(H2O)2]) were analyzed with the aid of the parametric Griffith Hamiltonian for the high-spin Co(ii) supported by the ab initio calculations of the crystal field (CF) parameters, g-factors and superexchange parameters between H-bonded Co(ii) ions in the neighboring molecules in a 1D network. This analysis suggests the presence of the easy axis of magnetic anisotropy and also shows the existence of a significant rhombic component. The detected frequency dependent (AC) susceptibility signal shows that complex I exhibits slow paramagnetic relaxation in the applied DC field belonging thus to the class of non-uniaxial field induced single ion magnets with a negative axial component of anisotropy. It is demonstrated that the main contributions to the relaxation come from the direct one-phonon process dominating at low temperatures, while the contribution of the two-phonon Raman process becomes important with increasing temperature.

The systematic studies of the electronic state of surface layers in organic semiconductor (DOEO)4[HgBr4] · TCE by X-ray photoelectron spectroscopy and UV photoelectron spectroscopy are performed. At temperatures below 50–70 K, a transition to the antiferromagnetic state is observed in inclusions having a different structure compared to the crystal bulk. According to transmission electron microscopy, there are two types of antiferromagnetic inclusions in the samples, with sizes of 2–5 and 100–400 nm. The contributions of antiferromagnetic inclusions and the spins of localized and free charge carriers (holes) to the total magnetic moment of the crystal are separated.

(DyPr)CoFeB microparticles are the building blocks of sintered magnets. The magnetic properties of powdered (DyPr)(CoFe)B microparticles and the effects of annealing, surface states, fixation of easy axis and magnetic dipole interaction on the magnetic hysteresis loop, and temperature dependencies of magnetization have been analyzed. Fixation of the annealed microparticles in polymer enhances the coercive field up to 11 times and the energy product up to six times. This fact indicates extraction of the true magnetic parameters from the magnetic measurements of powder. Thermal stability of the anisotropy field has been improved by the replacement of Fe atoms with Co atoms.

In this paper, we present a detailed study of the oscillating magnetic relaxation in the synthetic antiferromagnet (SAF) with two ferromagnetic Co layers of different thicknesses separated by an Ir spacer. The four stable magnetic states of the SAF are determined by the mutual alignment of magnetic moments in the layers and are controlled by both the magnetic interlayer exchange interaction and the Zeeman energy. The specific variations in the thicknesses of the layers and/or temperature allow the existence of a ``triple point,'' which corresponds to a coincidence of the critical switching fields for two or three interstate transitions. In this case, two or even three different types of magnetization reversals occur simultaneously and competitively. A nonmonotonic dependence of the domain-wall speed ${v}_{\mathrm{DW}}$ on magnetic field $H$ and an oscillating time dependence of magnetic moment $M$ in a constant magnetic field were observed in a Pt/Co/Ir/Co/Pt synthetic antiferromagnet with perpendicular anisotropy due to interplay between the magnetic nuclei produced by Dzyaloshinskii-Moriya interaction. The proximity of two or three (triple-point) critical fields of SAF switching is the necessary condition for both a nonmonotonic magnetic relaxation and the oscillating time variations of the magnetic moment. The dynamical model describing the interaction and subsequent evolution of the magnetic nuclei demonstrates that this nontrivial magnetic relaxation obeys a simple Schr\"odinger equation.

The physical origin of the magnetoplastic effect was experimentally identified in Al polycrystalline alloy. Exposure of the nominally pure industrial Al-Mg-Si-Fe alloy to magnetic field 0.7 T induces residual changes that provide a creep rate increase up to 25% and microhardness decrease down to 30%. FeAl inclusions of ∼1 μm size were revealed in the alloy. Magnetostriction of the ferromagnetic inclusions providing local mechanical stresses and generation of fresh dislocations in the vicinity of the inclusions is the main reason for magnetoplasticity. Ferro-, antiferro-, and paramagnetic contributions of the inclusions and/or Fe atoms distributed in the Al matrix have been distinguished. The chemical composition of FeAl inclusions determined by transition electron microscopy and local field probed by the Mossbauer technique are in good agreement with saturation magnetization of the FeAl alloys.The physical origin of the magnetoplastic effect was experimentally identified in Al polycrystalline alloy. Exposure of the nominally pure industrial Al-Mg-Si-Fe alloy to magnetic field 0.7 T induces residual changes that provide a creep rate increase up to 25% and microhardness decrease down to 30%. FeAl inclusions of ∼1 μm size were revealed in the alloy. Magnetostriction of the ferromagnetic inclusions providing local mechanical stresses and generation of fresh dislocations in the vicinity of the inclusions is the main reason for magnetoplasticity. Ferro-, antiferro-, and paramagnetic contributions of the inclusions and/or Fe atoms distributed in the Al matrix have been distinguished. The chemical composition of FeAl inclusions determined by transition electron microscopy and local field probed by the Mossbauer technique are in good agreement with saturation magnetization of the FeAl alloys.

International audience; The evolution of the switching field between stable states in MgO/CoFeB/Ta/CoFeB/MgO/GaAs and Pt/Co/Ir/Co/Pt/Ta/SiO2 synthetic ferrimagnets with perpendicular anisotropy as a function of the magnetic field sweeping rate (MFSR) 0.1-10 4 Oe/s has been studied. The most significant effect of the MFSR is an inversion of interstate transitions sequence. In the MgO/CoFeB/Ta/CoFeB/MgO/GaAs heterostructure, the increase of MFSR switches the dominant mechanism of magnetization reversal from propagation of domain walls to a nucleation of reversed magnetization areas. In Pt/Co/Ir/Co/Pt/Ta/ SiO2, the MFSR affects the final domain state of the transition, starting from the initial antiparallel configuration of the synthetic ferrimagnet.

In this article we report the synthesis and structure of the new Co(II) complex Et4N[CoII(hfac)3] (I) (hfac = hexafluoroacetylacetonate) exhibiting single-ion magnet (SIM) behavior. The performed analysis of the magnetic characteristics based on the complementary experimental techniques such as static and dynamic magnetic measurements, electron paramagnetic resonance spectroscopy in conjunction with the theoretical modeling (parametric Hamiltonian and ab initio calculations) demonstrates that the SIM properties of I arise from the nonuniaxial magnetic anisotropy with strong positive axial and significant rhombic contributions.

The relation between the macroscopic spontaneous magnetization reversal (magnetic viscosity) of (NdDySm)(FeCo)B alloys and the spectral characteristics of magnetic noise, which is caused by the random microscopic processes of thermally activated domain wall motion in a potential landscape with uniformly distributed potential barrier heights, is found.

It has been found that an increase in the Sm concentration in the range x = 0.05–0.18 in (Nd1‒x‒ySmxDyy)(FeCo)B supermagnets leads to a shift in the spin-reorientation transition temperature to higher values, whereas a Dy addition results in a decrease in the transition temperature. Single-ion anisotropy of Sm and Dy ions has different symmetry, making contributions of opposite signs to the resulting magnetic anisotropy of the lattice. Therefore, the threshold temperature TS of the spin-reorientation transition, which is determined by the balance of magnetic anisotropies of sublattices, can be controlled using ions with different symmetries.

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.

In ensembles of annealed ferrimagnetic alloy (DyPr)–(CoFe)–B microparticles in the free state and fixed in polymer, the coercivity differs more than by an order of magnitude. The contributions of orientation locking of magnetic axes of particles and the dipole magnetic interaction between particles to the coercivity and saturation magnetization field of an ensemble are discussed. In ensembles of unannealed microparticles, the effect of their locking and dispersing in polymer is significantly weaker.

It has been found that CoFeB–SiO2/C and CoFeB–SiO2/Bi2Te3 multilayer heterostructures with a cluster structure of CoFeB layers feature a long-range magnetic order in the entire temperature range from 2 to 300 K. At high temperatures (T = 300 K), CoFeB clusters exhibit magnetic properties characteristic of superparamagnets. At low temperatures (T = 5 K), clusters are ferromagnetic, and the easy magnetization axis is in the film plane. The temperature of the ferromagnetic-to-superparamagnetic state transition of clusters depends on a dielectric interlayer material: the use of Bi2Te3 instead of C as a spacer layer leads to an increase in the transition temperature by a factor of 4 and an increase in the magnetization blocking temperature of CoFeB clusters in a field of 100 Oe by a factor of 3.

The effect of small copper additions (to ∼6 at %) on the distribution of iron ions in six crystallographic sites of the unit cell of the main magnetic phase (PrDy)2(FeCo)14B has been detected. An increase in the copper concentration leads to a decrease in the 8j1 site occupation by iron ions. Independently of the presence of copper, the temperature dependences of the saturation magnetization of all samples have a minimum which can correspond to the presence of a low-temperature phase or a compensation point in grain boundary regions of the (PrDy)2(FeCo)14B main magnetic phase. The alloys under study are not additive sets of all phases in their composition, but behave as new materials with the mutual influence of phases on each other.

A series of two types of stochastic magnetization jumps in K0.4[Cr(CN)6][Mn(R/S)-pn](R/S)-pnH0.6 single crystals (pn = 1,2-diaminopropane) are reported. Large jumps appear on the demagnetization branch of the hysteresis loop at the critical value of the decreasing magnetic field. The correlation of the temperature dependence of jump magnetic field and the temperature dependence of magnetic anisotropy field indicates a contribution of magnetic anisotropy to nonlinear spin-soliton structure. Small magnetization jumps occur in both magnetization and demagnetization regimes.

It has been found that temperature dependences of the saturation magnetization of sintered hard magnetic (Pr,Dy,M)2(Fe,Co)14B (M = Gd, Sm, Nd) alloys demonstrate an increase at a temperature lower than a critical temperature (150 K for Sm and Nd and 70 K for Gd). An additive of copper does not influence the critical temperature. It has been assumed that there is a low-temperature phase in which cobalt is replaced with boron that diffuses from the (Pr,Dy,Gd)(Fe,Co)4B phase to the near-surface region of grains of the main magnetic (Pr,Dy,Gd)2(Fe,Co)14B phase.

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.

Single crystals and microcrystals Si: B enriched with 29Si isotopes have been studied using nuclear magnetic resonance and electron paramagnetic resonance (EPR) in the temperature range from 300 to 800 K. It has been found that an increase in the temperature from 300 to 500 K leads to a change in the kinetics of the relaxation of the saturated nuclear spin system. At 300 K, the relaxation kinetics corresponds to direct electron–nuclear interaction with inhomogeneously distributed paramagnetic centers introduced by the plastic deformation of the crystals. At 500 K, the spin relaxation occurs through the nuclear spin diffusion and electron–nuclear interaction with an acceptor impurity. It has been revealed that the plastic deformation affects the EPR spectra at 9 K.

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 redistribution of 28Si, 29Si, and 30Si isotopes in subsurface layers of Si: B single crystals after their plastic deformation has been revealed. It has been found that the distribution profile of 28Si and 29Si isotopes becomes smoother after deformation, whereas the 30Si isotope distribution remains unchanged. A change in the subsurface profile of the 29SiO oxide is observed, which indicates the migration of the 29Si isotope in the composition of oxygen complexes during plastic deformation.

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.

The differences in the hysteresis loops of the (DyPr)CoFeB ferrimagnetic alloy powders dispersed in a polymer and eicosane, in a free form, and in sintered samples, have been analyzed. It has been shown that the differences are determined by changes in the dipole–dipole interaction between microparticles upon their dissolution, as well as are determined by the mechanical rotation of the particles and the degree of pinning of their easy axes.

A first-order magnetic phase transition, accompanied by a decrease in magnetization and coercive force, occurs in nanoparticles that are diluted with superstrong magnets e-In0.043Fe1.957O3 at a temperature of T = 150 K. The phase transition consists of a re-orientation of the easy magnetization axis due to the competition between the single-ion and dipole-dipole magnetic anisotropies. Temperature hysteresis of magnetization is observed near the temperature of the spin-reorientation transition, which is explained by the delay in the new phase growth with the change of the direction of the easy axis. The jump in magnetization, caused by the spin-reorientation transition, is suppressed with increasing magnetic field.

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.

International audience; Aftereffect measurements have been performed on synthetic ferrimagnets showing strong perpendicular magnetic anisotropy, namely (Co/Pt)/Ir/(Co/Pt), by measuring the magnetization of the sample as a function of time for several different applied magnetic fields. Unexpected magnetic relaxation has been observed. Indeed, for some particular applied magnetic fields, the magnetization as a function of time first plummets and then increases. This nonmonotonic aftereffect can be understood by considering the possible magnetic states and the transitions between those states. This understanding has been confirmed and detailed using magneto-optical Kerr effect (MOKE) microscopy. Indeed, the measurements show nucleation and propagation of a transient metastable magnetic configuration. Furthermore, we were able to obtain a good qualitative agreement between a simple one-dimensional model and the experimental observation. We could strongly support the hypothesis that this peculiar nonmonotonic behavior could be a very general feature that should be observed in any antiferromagnetically coupled system (synthetic ferrimagnets, synthetic antiferromagnets) with perpendicular magnetic anisotropy.

International audience; Two synthetic antiferromagnet bilayer systems with strong perpendicular anisotropy CoFeB/Ta/CoFeB and Pt/Co/Ir/Co/Pt have been grown using sputtering techniques. For both systems two types of magnetization transitions have been studied. The first one concerns transitions from a state where magnetizations of the two magnetic layers are parallel (P state) to a state where magnetizations of the two layers are aligned antiparallel (AP state). The second one concerns transitions between the two possible antiparallel alignments (AP+ to AP−). For both systems and both transitions after-effect measurements can be understood in the frame of nucleation—propagation model. Time derivative analysis of magnetic relaxation curves and mapping of the first order reversal curves at different temperature allowed us to demonstrate the presence of different pinning centers, which number can be controlled by magnetic field and temperature.

International audience; Long magnetic relaxation (up to few hours) between stable magnetic states was analyzed in Pt/Co/Ir/Co/ Pt/GaAs heterostructures of different Co layers thickness. The experimental data were compared to a large variety of theoretical models amongst which the Fatuzzo-Labrune one seems to be the more relevant. The contributions from domain nucleation and domain wall motion to magnetic relaxation of the spin valves were separated and evaluated. The increase of Co layer thickness suppresses the domain nucleation and enhances the domain wall propagation. The obtained data provide an understanding of the limitations of switching time in the spin valves of large area necessary for GMR biosensors.

International audience; A multilayer Pt/Co/Ir/Co/Pt/GaAs heterostructures demonstrates a long term (to several hours) magnetic relaxation between two stable states of the magnetization of the system. The magnetization reversal of the heterostructure layers occurs both due to the formation of nuclei of the reverse magnetization domains and as a result of their further growth by means of motion of domain walls. The competition between two these processes provides a nonexponential character of the magnetic relaxation. At 300 K, the contributions of these processes to the relaxation are commensurable, while, at temperatures lower than 200 K, the contribution of the nucleation is suppressed and the magnetic relaxation occurs as a result of motion of the domain walls.