Variations in the physical properties of 2D semiconductors due to differing growth conditions present challenges for the reliable design of nanodevices. In this study, we analyzed the chemical composition and physical properties of several commercially grown CrSBr samples and observed that detailed characterization can reveal differences in magnetic and optical properties, which can be explained by crystal heterogeneity. A reduction in bromine content was clearly detected in bulk material through magnetic studies, although it was not always identified by Raman scattering. The samples exhibited variations in chemical composition due to bromine depletion in one of them. This depletion led to a shift in the critical temperature for a paramagnetic-tometamagnetic transition from 132 K to 120 K in the non-stoichiometric sample. The critical temperature of 120 K, along with XRD spectra, aligns well with those typical of the Cr2S3 phase. Bromine depletion promotes the nucleation of the Cr2S3 phase, which coexists with the primary CrSBr phase. Mechanical exfoliation of brominedepleted CrSBr crystals produced single flakes with characteristic CrSBr spectra, along with a small number of additional flakes exhibiting different compositions. We further investigated the mechanical properties of CrSBr bulk material. In the surface layer (up to 0.5 mu m deep), we observed deviations in nanohardness relative to the bulk material. Nanoindentation measurements revealed a hardness of 3 GPa and a Young's modulus of 45 GPa at deeper indentation into the bulk.

Chiral molecular magnets are important platforms for investigation of non-linear spin phenomena. Mapping of imaginary and real parts of magnetic susceptibility in coordinates field-temperature revealed two spin transitions at 15 K and 21 K in chiral 2D metal-organic ferrimagnet [Mn-II(HL-pn)(H2O)][Mn-III(CN)6]center dot 2H(2)O titled Brown Needle crystals. Curie temperature corresponds to 21 K, while the transition between ferrimagnetic and spin canting incommensurate phase happens at 15 K. We found that the second and third harmonics of non-linear magnetic susceptibility correspond to time irreversible domain walls displacement. High frequency spin relaxation was monitored by electron spin resonance (ESR) technique. Resonant line at zero field was analyzed in the frame of formalism developed for non-Kramers ions coupled by dipole-dipole interaction. The zero field ESR spectra originates from the S = 2 ground state of the Mn3+ ions. This line appears in a narrow temperature range 18-22 K indicating the intermediate magnetic phase arising in the vicinity of the Curie point. Microwave power saturation of the ESR line corresponds to a fast relaxation similar to 10 ns. We found the significant difference in this relaxation time in racemic and chiral crystals. Resonant response of the Mn3+ ions controlled by dipole-dipole magnetic interaction provides very sensitive indication of crystal fields their modification and it allows one to judge on origin critical phenomena at magnetic phase transition.

Interaction between single molecule magnets (SMMs) and metal surface is a hot topic promising controllable deposition of SMMs, programmable frequency of magnetic relaxation and addressed reading of information. In this paper, we develop strategy of the Er3+ based SMM functionalization by its penetration inside the arrays of Ferromagnetic Micro Particles (FMPs). We show that predictable residual magnetic field of the FMPs arrays is an effective tool for regulation of the frequency maximum of imaginary magnetic susceptibility. We analyzed color of magnetic noise in respect to physical origin of magnetic relaxation. An additional channel for control over spin noise is formation of chemical bonds between SMM and the FMPs surface. Oxidation of an Er complex transforms 20 +/- 5 % of the initial 10 -coordinated SMM complex to the 9 -coordinated complex with reduced relaxation time. Memorized residual magnetization of the composite material allows one to set desirable relaxation frequency in the individual micronized cells to create a sound frequency register. The proposed compaction of SMMs of different types in ferromagnetic composites provides engineering of the chemically designed spin interface on ferromagnetic surface for spintronics and quantum computing.

Reactions of 12H-quinoxaline[2,3-b]phenoxazine (QOPO) derivatives with the CoII and ZnII hexafluoroacetylacetonates accompanied by protonation of the starting bases result in stable complexes [QOPOH]+[M(hfac)3]− whose structure was determined by X-ray diffraction and by 1H and 15N NMR spectroscopy. The complexes are characterized by long-wavelength absorption (560–664 nm) and fluorescence in the red region (λfl = 674–805 nm). The relative energies of the protonated tautomers N(14)—H and N(7)—H were determined using the results of B3LYP–D3BJ/6-311G++(d,p) density functional calculations with inclusion of D3BJ dispersion correction. A SQUID magnetometry study of the static and dynamic magnetic properties of the CoII complex revealed that it behaves as a field-induced single-ion magnet.

Multiple noncollinear spin structures and transitions between them initiated by field and temperature attract attention due to extraordinary coexistence of complicate spin phases in Ho. We explore the magnetic relaxation dynamics within thin films undergoing transitions between ferromagnetic (FM) and helix states. Employing susceptibility measurements at a relatively high frequency range (~100-1500 Hz) and magnetic viscosity measurements at a lower frequency (~0.01 Hz), we focus on Ho films with a thickness of 400 nm. Notably, sharp variations in the real and imaginary components of magnetic susceptibility are discerned during the FM—Helix transition, occurring at temperatures between 15-30 K. Hysteresis effects in the magnetic susceptibility components are identified during cyclic variations in the external field, indicating a relatively rapid process with a timescale of approximately 10 ms accompanying the FM—Helix transition. The slow relaxation process is also found to exhibit sensitivity to this transition. Furthermore, the field dependence of magnetic viscosity displays a marked decline at the FM—Helix transition. The proposed research methodologies for investigating relaxation processes in materials with multiphase spin structures are deemed universally applicable and offer insights into transitions between spin states in materials manifesting non collinear spin structures.

In single-ion complexes based on Co 2+ ions, the second and third harmonics of the magnetic susceptibility were found at temperatures of 2-4 K, which exceed the Neel temperature. The maxima of the second and third harmonics of the magnetic susceptibility are observed at a frequency of ~1 Hz, at which the maximum of the first harmonic is observed in a field of 3.2 kOe. An analysis of the dependences of the second and third harmonics of the magnetic susceptibility on the field and temperature showed that the nonlinearity arises as a result of the formation of a spin glass state at temperatures slightly higher than the Neel temperature. In this state, there is no long-range spin order, but there are spin clusters in the spin glass state. The spin-glass state in a compound with a Co 2+ ion with a high magnetic anisotropy is unusual in that the exchange interaction is much smaller than the single-ion anisotropy energy. Keywords: molecular magnets, nonlinear magnetic susceptibility, nanostructures, spin dynamics, spin glass.

Ferromagnetic microparticles significantly affect spin relaxation in the Er3+ single-ion magnet sandwiched in a composite material. The balance of thermal spin noise corresponding to Orbach, Raman, quantum tunneling, and direct relaxation channels is shifted in Er3+ complexes under the influence of surrounding ferromagnetic matrix. There are two competing sources of the electron spin noise controlled by ferromagnetic media. First, internal residual magnetic field delays spin relaxation in the Er3+ complexes due to the Zeeman interaction of the Er3+ spin even in the absence of external magnetic field. Second, chemical bonding between the Er 4d shell and the O 1s shell accelerates magnetic relaxation in the Er3+ ions on the surface of microparticles. Significance of these results is that composite media can be sliced into small elements with a variable frequency of spin noise depending on individual magnetization programmed within each element.

A new method is developed to control the spin relaxation in single-molecular magnets (SMMs) in order to eliminate spin decoherence to the level acceptable for quantum computing at a relaxation frequency of about 10(2) Hz and a temperature of 2 K. A significant part of the SMMs has rapid magnetic relaxation proceeding through several parallel channels sensitive to the presence of an external magnetic field. Some of the relaxation channels in such materials (also called single-ion magnets (SIMs)) are suppressed using an electromagnet in macroscopic volumes of complexes. This is unacceptable when individual SIM complexes are used as qubits and forces us to look for ways to use a local magnetic field and other types of complex interactions in a specially selected environment, which provides the Zeeman interaction in the absence of an external field. We demonstrate that a composite material made of SIM complexes with Er3+ ions and ferromagnetic microparticles exhibits a remanent magnetization, which is sufficient to decrease the spin relaxation frequency in the volume. In magnitude, this effect competes with the well-known effect of hybridization of the orbitals of a complex during its interaction with a metallic surface. Therefore, the microstructuring of an array of complexes in a ferromagnetic matrix can be used to create local regions with a controlled magnetic relaxation frequency.

In monoionic complexes based on Co2+ ions, the second and third harmonics of the magnetic susceptibility were found at temperatures of 2–4 K, which exceed the Néel temperature. The maxima of the second and third harmonics of the magnetic susceptibility are observed at a frequency of ~1 Hz, at which the maximum of the first harmonic is observed in a field of 3.2 kOe. An analysis of the dependences of the second and third harmonics of the magnetic susceptibility on the field and temperature showed that the nonlinearity arises as a result of the formation of a spin glass state at temperatures slightly higher than the Néel temperature. In this state, there is no long-range spin order, but there are spin clusters in the spin glass state. The spin-glass state in a compound with a Co2+ ion with a high magnetic anisotropy is unusual in that the exchange interaction is much smaller than the single-ion anisotropy energy.

Four compounds are synthesized by the reactions of rare-earth metal(III) nitrates with 2-mercaptopyridine-N-oxide (HSC5H4NO) in water-alkaline solutions: [Pr2(SC5H4NO)6(H2O)2] (I), [Tb2-(SC5H4NO)6(H2O)2] (II), [Ho2(SC5H4NO)6(H2O)2] (III), and [Er2(SC5H4NO)6(H2O)2] (IV). Their synthesis and results of X-ray diffraction studies are presented. Each metal ion in the binuclear complexes forms the octacoordinated structure including two SC5H4NO ligands, which coordinate each metal ion (3+) via the chelate mode (through S and O), two bridging oxygen atoms belonging to two SC5H4NO, and two molecules of coordination water. The product χT and effective magnetic moment (μeff) remain unchanged in the synthesized complexes in the temperature range from 300 to 150 K as found by SQUID magnetometry. At T < 150 K in complexes I (Т < 30 K) and II (T < 50 K), μeff decreases with decreasing temperature, which possibly indicates a magnetic transition and an antiferromagnetic interaction between the Pr3+ and Tb3+ ions. An increase in μeff with decreasing temperature and a sharp decrease at T < 10 K are observed in complex III, whereas in complex IV μeff increases smoothly with decreasing temperature. This can indicate the appearance of ferromagnetic correlations in complex IV. No magnetic relaxation response is observed for complex I in the whole frequency range of the alternating field (AC) HAC from 0.2 to 1400 Hz both in the bias field and without it. The field dependences of the magnetic moment at 2 and 5 K для complexes II–IV are characteristic of paramagnetics at these temperatures. At T = 2 K the samples exist in the same spin state as at T = 300 K: cooling does not change the spin state of the Tb3+, Ho3+, and Er3+ ions in the complexes. No magnetic hysteresis is observed at low temperatures (2 and 5 K) in these complexes. The dependences of the real and imaginary components of the magnetic susceptibility on the AC frequency for complexes II–IV are obtained in the absence of a direct field (DC) and in the bias field. The Cole-Cole diagrams demonstrate the relaxation mode of the domain wall motion and no shift of a maximum of the imaginary component with changing temperature (tunneling relaxation mechanism) in complexes II–IV.

Here we present the effect of ferromagnetic magnetoresistive sensor on magnetic susceptibility of nanoparticles (NPs) deposited on its surface. Deposition of the CoFe2O4 nanoparticles on the CoFeB/Ta/CoFeB platform, comprising thin ferromagnetic layers, changes the blocking temperature of the NPs. The magnetic dipole interaction between the NPs and the platform affects the frequency and field dependences of the blocking temperature of the NPs, because the effective energy barrier of magnetization reversal is higher than in NPs deposited on a diamagnetic substrate. Obtained results demonstrate backward effect of the sensor on the analyzing NPs array. An allowance of this effect is important for the correct application of a magnetoresistive and low frequency inductive sensors in medicine and biology.

The effect of nanoparticles (NPs) on microwave magnetoresistance in MgO/CoFeB(free)/Ta/CoFeB(fixed)/MgO)/Ta platform and the effect of individual NP on free CoFeB ferromagnetic layer magnetization have experimentally been revealed and analyzed. The area of the platform where magnetization is inverted under scattering field of NPs has been observed. Micromagnetic modeling of dipole magnetic interaction confirms the existence of such areas in "NP-platform" system. The increase in critical field of the platform and the change of resistance under scattering field on NPs have experimentally been revealed.

The quantum tunneling of magnetization accelerates magnetic relaxation in transition and rare-earth ion complexes and often leads to the degradation of the characteristics of single-molecule or single-ion magnets. On the other hand, the applied dc magnetic field slows down the quantum tunneling of magnetization and favors other channels of spin relaxation. In this work, the stray magnetic field related to ferromagnetic microparticles occurring in the SIM composite with PrDyFeCoB microparticles is proposed instead of the applied field. The adjustable remanent magnetization of microparticles makes it possible to control the required stray field, which can be used to tune the spin relaxation rate in the complexes surrounding the microparticles. In this case, a slow spin relaxation is observed at zero applied field.

In this paper, we present the study of domain structure accompanying interstate transitions in Pt/Co/Ir/Co/Pr synthetic ferrimagnet (SF) of 1.1 nm thick and 0.6 – 1.0 nm thin ferromagnetic Co layers. Variation in the thickness of the thin layer causes noticeable changes in the domain structure and mechanism of magnetization reversal revealed by MOKE (Magneto-Optical Kerr Effect) technique. Magnetization reversal includes coherent rotation of magnetization of the ferromagnetic layers, generation of magnetic nuclei, spreading of domain walls (DW), and development of areas similar with strip domains, dependently on thickness of the thin layer. Inequivalence of the direct and backward transitions between magnetic states of SF with parallel and antiparallel magnetizations was observed in sample with thin layer thicknesses 0.8 nm and 1.0 nm. Asymmetry of the transition between these states is expressed in difference fluctuation fields and shapes of reversal magnetization nucleus contributing to the correspondent forward and backward transitions. We proposed simple model based on asymmetry of Dzyaloshinskii–Moriya interaction. This model explains competition between nucleation and domain wall propagation due to increase/decrease of the DW energy dependently on direction of the spin rotation into the DW in respect to external field.

The effect of the stray field of Fe/Fe3O4 nanoparticles on the angular dependence of the microwave absorption derivative in CoFeB/Ta/CoFeB synthetic ferrimagnetic structures and CoFeB films with perpendicular anisotropy is analyzed, and its application for sensor technology is proposed. The effective field of the "platform-particles" system controlled by the magnetic dipole interaction of the CoFeB-Fe/Fe3O4 system decreased to zero in areas where the platform was magnetostatically coupled with nanoparticles. Micromagnetic modeling demonstrated the distribution of magnetization and resistance in local areas of CoFeB/Ta/CoFeB structures under the nanoparticles. The microwave absorption derivative can be used as an indicator of local magnetization switching of the giant magnetoresistance (GMR) structure under scattering fields of NPs or magnetically labeled cells. The limiting sensitivity of the detection method was 2.4 × 107 nanoparticles, which covered the spin-valve surface. We have proposed to combine the advantages of a GMR sensor with wireless technology of microwave reading of magnetoresistance for the detection of magnetically labeled cells.

We report a study of the response function parameters (amplitude and rise/fall time) of a high-speed GaSb/GaInAsSb/GaAlAsSb photodiode operating at 1.9 µm as a function of optical input power and reverse bias voltage. The experimental measurement results yield the optimal pulse energy and optimal reverse bias voltage for the photodiode. The 44 ps minimal rise time of the response function and 3.6 GHz bandwidth are achieved under a 3 V reverse bias voltage and pulse energy in the 0.27–2.5 pJ range.

We report a study of the response function parameters (amplitude and rise/fall time) of a high-speed GaSb/GaInAsSb/GaAlAsSb photodiode operating at 1.9 µm as a function of optical input power and reverse bias voltage. The experimental measurement results yield the optimal pulse energy and optimal reverse bias voltage for the photodiode. The 44 ps minimal rise time of the response function and 3.6 GHz bandwidth are achieved under a 3 V reverse bias voltage and pulse energy in the 0.27-2.5 pJ range.

The magnetization reversal of the MgO/CoFeB/Ta/CoFeB/MgO/Ta/GaAs heterostructures and the ultrathin MgO/CoFeB/MgO/Ta/GaAs films with a perpendicular anisotropy in the magnetic field of clusters of Fe/Fe 3 O 4 nanoparticles is experimentally observed. The stray magnetic field of Fe/Fe 3 O 4 nanoparticles increases the field of switching the magnetization of spin valves and monolayer platforms. The size of the magnetization reversal region of the ferromagnetic platform under Fe/Fe 3 O 4 nanoparticles as a function of the cluster size was determined by atomic force and magnetic force microscopy. The size of the magnetization reversal region is found to be larger than the particle cluster size, which is caused by the stray field of a cluster of Fe/Fe 3 O 4 nanoparticles. The local magnetization orientations in the CoFeB layers under clusters of nanoparticles and the magnetization reversal region diameter are determined as functions of the magnetic moment and the size of the cluster using micromagnetic simulation.

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.