Search Results (60)

[Mn^III(pyrol)₃(tren)] {(Hpyrol)₃tren = tris(1-(2-azolyl)-2-azabuten-4-yl)amine)} is a mononuclear spin-transition compound switching between high spin (HS, S = 2) and low spin (LS, effective S = 1) around 47 K, preserving I$\overline{4}$3d symmetry. Its magnetic anisotropy is studied by calculating the atomic susceptibility tensor from the refinement of polarized neutron powder diffraction. The analysis reveals that the weakly prolate-type atomic magnetic anisotropy in the HS state abruptly switches to uniaxial needle-shaped/Ising-type anisotropy in the LS state. However, the overall magnetic anisotropy of the unit cell remains isotropic due to the cubic nature of the crystal symmetry. Irreversible coexistence of mixed spin states HS/LS is observed in the vicinity of the cooperative spin crossover, where the average magnetic moment of Mn³⁺ shows a hysteretic temperature variation. This hysteretic mixing of HS and LS at intermediate temperatures suggests complex growth and nucleation of HS and LS domains. The study demonstrates that polarized powder neutron diffraction is a unique and powerful tool for describing complex magnetic anisotropies and magneto-structural correlations in molecular-based magnetic materials. Full article

Metal magnetic memory (MMM) is a promising non-destructive evaluation method for ferromagnetic materials, allowing early detection of stress concentration and micro-defects under weak geomagnetic excitation. However, current magneto-mechanical coupling models are computationally complex and insufficient to characterize the full-cycle evolution of mesoscale physically short cracks. This work proposes a magnetic dipole model and its decomposed formulation for V-shaped cracks. Combined with theoretical derivation, finite element simulation, and in situ three-point bending tests on Q345 steel, the magneto-mechanical coupling mechanism and magnetic signal evolution during crack propagation are investigated. Results show that the MMM normal component exhibits obvious peak-peak features at the crack tip, while the tangential component shows a single-peak characteristic. Two critical signal mutations are observed at crack lengths of about 100 μm and 3000 μm, corresponding to micro-meso and meso-macro crack transitions, respectively. The model is verified with relative errors of 15.2% for H_x and 17.6% for H_y. This study reveals the quantitative correlation between MMM signals and full-lifecycle crack growth, supporting damage assessment and fatigue life prediction for ferromagnetic engineering structures. Full article

The ligand-driven self-assembly of metal clusters offers a powerful strategy for constructing discrete molecular architectures with tunable magnetic and structural properties. By judiciously selecting appropriate multidentate ligands, researchers can direct the formation of polynuclear metal assemblies with diverse nuclearities, geometries, and topologies. Coordination-driven processes commonly stabilize such assemblies where multidentate ligands operate as templates and linkers. These will also determine how the metal centers are arranged in space and how they connect to each other. These clusters can take on shapes that range from basic bridging dimers to more complicated icosahedral and cubane-type motifs. They often have excellent symmetry and strong frameworks. Magnetically, these clusters are a great place to study exchange interactions, spin frustration, and the behavior of single-molecule magnets (SMMs). The magnetic characteristics depend on things like the type of metal ions, the bridging ligands, the overall shape, and the local coordination environment. Interestingly, a large number of ligand-assembled clusters exhibit high spin ground states and slow magnetization relaxation, which makes them attractive options for quantum information storage and molecular spintronic devices. This review connects coordination chemistry, supramolecular design, and molecular magnetism of pyridine–amine–carboxylate frameworks, offering insights into fundamental magnetic phenomena and guiding the development of next-generation functional materials. Continued exploration of ligand frameworks and metal combinations holds the potential to yield novel clusters with enhanced or unprecedented magnetic characteristics. Full article

The Wiegand effect is a nonlinear magnetic phenomenon observed in specially processed Wiegand wires, representing a macroscopic manifestation of the Barkhausen effect. It is characterized by a large, sharp Barkhausen jump in the wire’s magnetization curve under an external alternating magnetic field. However, the underlying magnetic structure of these wires and the precise mechanism responsible for the Wiegand effect remain inadequately understood. In this study, we propose a conceptual model for the magnetic structure of Wiegand wires. Experimental samples with varying diameters were prepared through FeCl₃ solution etching. The magnetic properties of individual layers within the wire were systematically investigated using the surface magneto-optic Kerr effect, Wiegand pulse measurements, and minor hysteresis loop analysis. By correlating these experimental results with JMAG simulations based on the proposed magnetic structure model, we elucidate the layer-by-layer magnetization reversal processes under alternating magnetic fields and clarify the fundamental mechanism that triggers the large Barkhausen jump. Full article

Geomagnetic activity reflects the complex coupling between the solar wind, magneto-sphere and ionosphere. While the global Kp index serves as a standard proxy for geo-magnetic disturbances, it obscures regional variations linked to local current systems and ionospheric conductivity. This study investigates regional features of geomagnetic activity using the local K index from the Almaty (AAA) observatory and compares its temporal dynamics with Kp for 2007–2025. A combination of statistical, spectral, wavelet, and nonlinear methods was applied, including power spectral density, continuous and cross-wavelet transforms, multifractal detrended fluctuation analysis, and permutation entropy. These approaches capture both linear and nonlinear features of variability and reveal scale-dependent structures in geomagnetic fluctuations. The results show a high correlation (r ≈ 0.84) between K (AAA) and Kp, but with a consistent positive offset of the local index, indicating sensitivity to regional ionospheric processes. Wavelet coherence highlights strong coupling in the 13–27-day band associated with solar rotation. Multifractal spectra reveal broader, more heterogeneous scaling in Kp and narrower, more intermittent dynamics in K during disturbed periods. Local indices, like K (AAA), thus provide essential insight into mid-latitude electrodynamics, complementing global measures in characterizing the nonlinear spatio-temporal complexity of geomagnetic activity. Full article

This study investigates the dynamic magneto-optical properties of ferrofluid thin films, focusing on how magnetic fields induce light–matter interactions using a device known as Ferrocell. Our findings reveal that incident light interacts with self-assembled, anisotropic nanoparticle structures, transforming the ferrofluid into a highly responsive optical medium. Monochromatic laser experiments confirmed the direct correlation between laser color and diffracted light color offering direct insights into particle orientation and aggregate morphology. We observed significant chromatic shifts, especially in regions under strong perpendicular magnetic fields, which provide compelling evidence of structural colors. This phenomenon stems from wavelength-selective interference and diffraction, reminiscent of photonic crystal behavior, yet characterized by short-range order, classifying the material as a photonic glass. Full article

To develop single molecule magnets, a dinuclear complex [Dy₂(HOBQ)₄Cl₆] (1) was prepared from the reaction of DyCl₃ with benzo[h]quinolin-10-ol (HOBQ). Each Dy(III) ion shows a compressed octahedral geometry and the two Dy(III) ions in 1 are bridged by two Cl⁻ ligands to construct a dinuclear structure with the four HOBQ ligands on the axial positions and six Cl⁻ ligands in the equatorial plane. Magnetic measurements showed that complex 1 is a field-induced single molecule magnet having an obvious magnetic hysteresis loop with an energy barrier of 71(2) K. These experimental results are corroborated by the ab initio complete active space self-consistent field (CASSCF) calculations which also interpret the magneto-structural correlation. It is a typical example to achieve Dy(III) SMM through regulating coordination geometry, i.e., lengthening equatorial coordination bonds and shortening axial ones to form a compressed octahedral geometry. Full article

Hetero-bridged dinuclear oxidovanadium(IV) complexes, [(VO)₂{HB(pz}₃}₂(μ-OH)(μ-O₂CR)] [R = C₂H₅, 1; (CH₃)₃C, 2; (CH₃)₃CCH₂, 3; Ph₂CH, 4; Ph₃C, 5; PhCH₂CH₂, and 6; {HB(pz)₃}⁻ = hydrotris(pyrazolyl)borate], were synthesized and characterized using X-ray crystallography, infrared spectroscopy, UV-VIS spectroscopy, and elemental analysis. Structure analysis revealed that these complexes adopt a μ-hydroxo-μ-carboxylato hetero-bridged dinuclear structure. Magnetic measurements revealed ferromagnetic interactions (J ~ +20 cm⁻¹) between two V(IV) ions. Full article

A preprocessing technique named “spiral annealing” was applied for the first time to magnetic microwires. In this process, the sample was arranged in a flat spiral shape during annealing, and subsequent measurements were conducted on the unbent sample with the induced stress distribution along and transverse to the sample. The research utilized both magnetic and magneto-optical methods. The anisotropy field magnitude in both the volume and surface of the microwire was measured, and for the first time, a direct correlation between the anisotropy field and the curvature of a spirally annealed microwire was established. Additionally, a connection between the type of surface domain structure and the degree of spiral curvature was identified. The preservation of the distribution of spiral annealing-induced magnetic properties both along and across the microwire is a key effect influencing the technological application of the microwire. The range of induced curvature within which a specific helical magnetic structure can exist was also determined. This insight links the conditions of spiral annealing to the selection of microwires as active elements in magnetic sensors. Full article

The reaction of Mn(II) salts in the air with different R-salicylaldehyde oximes and the sodium or cesium salts of 9-anthracenecarboxylato (9-AC) allows for the isolation of new six polynuclear compounds: [Mn₃NaO(salox)₃(9-AC)₂(EtOH)₃H₂O]_n·2EtOH (1), [Mn₃NaO(3-Me-salox)₃(9-AC)₂(EtOH)₃H₂O]_n·EtOH (2), [Mn₆O₂(salox)₆(9-AC)₂(EtOH)₂(H₂O)₂]·3EtOH (3), [Mn₃O(3-Me-salox)₃(9-AC)(EtOH)₃(H₂O)]·1.8EtOH·3H₂O (4), [Mn₆O₂(Me-salox)₆(9-AC)₂(EtOH)₄(H₂O)₂]·0.5H₂O (5), and [Mn₆O₂(Et-salox)₆(9-AC)₂(EtOH)₄(H₂O)₂]·3EtOH (6). H₂salox is a salicylaldehyde oxime, H₂(3-Me-salox) is a 3-methyl-salicylaldehyde oxime, H₂Me-salox is a 1-(2-hydroxyphenyl)ethan-1-one oxime and a H₂-Et-salox is 1-(2-hydroxyphenyl)propan-1-one oxime. Structurally, compounds 1 and 2 consist of chains of trinuclear {Mn^III₃(μ₃-O)(salox)₃}⁺ units connected by Na⁺ ions. Compounds 3, 5, and 6 are hexanuclear units formed by two parallel trinuclear units {Mn^III₃(μ₃-O)(salox)₃}⁺ or {Mn^III₃(μ₃-O)(Me-salox)₃}⁺ planes related through an inversion center. Compound 4 consists of two isolated [Mn₃O(3-Me-salox)₃(9-AC)(EtOH)₃(H₂O)] trinuclear molecules in the unit cell showing crystallographic differences. Magnetic studies reveal a set of antiferromagnetic interactions in compounds 1 and 2 and a combination of antiferromagnetic and ferromagnetic interactions in compounds 3, 5, and 6. In all cases, the magneto-structural correlation between the intramolecular Mn^III-N-O-Mn^III torsion angle and the magnetic exchange within these units have been confirmed. For compounds 5 and 6, ac magnetic measurements reveal the slow relaxation of magnetization with moderate energy barriers of 19.9 cm⁻¹ and 31.1 cm⁻¹, respectively. Absorbance and fluorescence measurements in solution show the transitions of the 9-anthracenecarboxylate chromophore for all the compounds. Full article

A plethora of antiferromagnetic structures have been so far found in condensed matter physics, where the antiferromagnetic phase transition is characterized by symmetry lowering under the magnetic point group. Depending on the types of symmetry lowering, various cross-correlation phenomena, such as the anomalous Hall effect, magneto-electric effect, and magneto-piezoelectric effect, emerge below the critical temperature. We revisit a close relationship between the symmetry of the antiferromagnetic structures and cross-correlations based on the augmented multipoles consisting of electric, magnetic, magnetic toroidal, and electric toroidal multipoles with different spatial inversion and time-reversal parities. The symmetry classification will be useful for further exploration of functional antiferromagnetic materials. Full article

We present theoretical investigations examining the electronic and magnetic properties of the SmFe_12−xMo_x (x = 1, 2) and SmFe₁₀Mo₂H compounds, including magneto-crystalline anisotropy, magnetic moments, exchange-coupling parameters, and Curie temperatures. The spin-polarized fully relativistic Korringa–Kohn–Rostoker (SPR-KKR) band structure method has been employed, using the coherent potential approximation (CPA) to deal with substitutional disorder. Hubbard-U correction was applied to the local spin density approximation (LSDA+U) in order to account for the significant correlation effects arising from the 4f electronic states of Sm. According to our calculations, the total magnetic moments increases with H addition, in agreement with experimental data. Adding one H atom in the near-neighbor environment of the Fe 8j site reduces the magnetic moments of Fe 8j and enhances the magnetic moment of Fe 8f. For every investigated alloy, the site-resolved spin magnetic moments of Fe on the 8i, 8j, and 8f sites exhibit the same magnitude sequence, with $m_s^{Fe}$ (8i) > $m_s^{Fe}$ (8j) > $m_s^{Fe}$ (8f). While the addition of H has a positive impact on magneto-crystalline anisotropy energy (MAE), the increase in Mo concentration is detrimental to MAE. The computed exchange-coupling parameters reveal the highest values between the closest Fe 8i spins, followed by Fe 8i and Fe 8j spins, for all investigated alloys. The Curie temperature of the alloys under investigation is increased by decreasing the Mo concentration or by H addition, which is qualitatively consistent with experimental findings. Full article

Direct measurements of the magnetocaloric effect were performed in a Heusler Ni_44.4Mn_36.2Sn_14.9Cu_4.5 alloy at cryogenic temperatures in magnetic fields up to 10 T. The maximum value of the inverse magnetocaloric effect in a 10 T field was ∆T_ad = –2.7 K in the vicinity of the first-order magnetostructural phase transition at T₀ = 117 K. Ab initio and Monte Carlo calculations were performed to discuss the effect of Cu doping into a Ni-Mn-Sn compound on the ground-state structural and magnetic properties. It is shown that with increasing Cu content the martensitic transition temperature decreases and the Curie temperature of austenite slightly increases. In general, the calculated transition temperatures and magnetization values correlated well with the experimental ones. Full article

The metal–radical approach is a well-established synthetic way toward multi-spin systems that relies on the coordination of stable radical ligands with transition metal ions. The advantage offered by the use of paramagnetic ligands is that metal–radical magnetic exchange coupling is direct between the magnetic orbitals of the radical and metal ion. With the aim of further exploring this approach, crystals of four heterspin complexes, [M(hfac)₂L^F]₂ {M = Mn, Co, or Ni and hfac = hexafluoroacetylacetonate} and [Cu(hfac)₂L^F]_n, were obtained using a new fluorinated pyrazolyl-substituted nitronyl nitroxide radical, 4,4,5,5-tetramethyl-2-(5-fluoro-1-methyl-1H-pyrazol-4-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L^F) as a ligand. The newly synthesized complexes were fully characterized, including X-ray crystallography and magnetometry. XRD analysis revealed that complexes [M(hfac)₂L^F]₂ have similar dimer structures in which a metal ion is in a six-coordinated environment with four O atoms from the two hfac ligands, one radical O atom, and one pyrazole N atom from ligand L^F. Nonetheless, the packing patterns of the complexes were found to be considerably different. In [Mn(hfac)₂L^F]₂, there are no magnetically important short contacts between manganese dimers. By contrast, in [Co(hfac)₂L^F]₂ and [Ni(hfac)₂L^F]₂, there are short contacts between non-coordinate O atoms of nitronyl nitroxide moieties. Magnetic behaviors of [M(hfac)₂L^F]₂ showed that the M ions and the directly coordinated radicals are strongly antiferromagnetically coupled (J_Mn-ON = −84.1 ± 1.5 cm⁻¹, J_Co-ON = −134.3 ± 2.6 cm⁻¹, and J_Ni-ON = −276.2 ± 2.1 cm⁻¹; $\widehat{H}=-2J{\widehat{\stackrel{⃑}{S}}}_{\mathrm{M}}{\widehat{\stackrel{⃑}{S}}}_{\mathrm{N}\mathrm{O}}$). Notably, the magnetization of [Mn(hfac)₂L^F]₂ having molecular structure proved to be accompanied by hysteresis. The [Cu(hfac)₂L^F]_n complex has a chain-polymer structure with alternating magnetic fragments: three spin exchange clusters {O_NO–Cu(II)–O_NO} and {Cu(II)} ions. Despite the direct coordination of radicals, its magnetic properties are weakly ferromagnetic (J_Cu-ON = 14.8 ± 0.3 cm⁻¹). Full article

Functional dependence of the axial zero-field splitting parameter D with respect to a properly chosen geometrical parameter (D_str) in metal complexes is termed the magnetostructural D-correlation. In mononuclear hexacoordinate Ni(II) complexes with the ground electronic term ³B_1g (³A_2g in the regular octahedron), it proceeds along two intercepting straight lines, allowing for predicting the sign and magnitude of the D-parameter by knowing the X-ray structure alone; D_str is constructed from the metal–ligand bond lengths. In hexacoordinate Co(II) complexes, it is applicable only in the segment of the compressed bipyramid where the ground electronic term ⁴B_1g is orbitally non-degenerate so that the spin Hamiltonian formalism holds true. The D vs. D_str correlation is strongly non-linear, and it is represented by a set of decreasing exponentials. In tetracoordinate Co(II) complexes, on the contrary, the angular distortion from the regular tetrahedron is crucial so that the appropriate structural parameter D_str is constructed of bond angles. The most complex case is represented by pentacoordinated Co(II) systems, for which it is not yet possible to define a statistically significant correlation. All of these empirical correlations originate in the electronic structure of metal complexes that can be modelled using generalized crystal-field theory. As the barrier to spin reversal in single-molecule magnets is proportional to the D-value, for rational tuning and/or prediction of the single-molecule magnetic behaviour, knowledge/prediction of the D-parameter is beneficial. In this review, we present the statistical processing of an extensive set of structural and magnetic data on Co(II) and Ni(II) complexes, which were published over the past 15 years. Magnetostructural D-correlations defined for this data set are reviewed in detail. Full article