Magnetochemistry, Volume 9, Issue 11 (November 2023) – 9 articles

Among the 5d transition metal iridates, Sr₂IrO₄, which has a layered chalcogenide structure, has received much attention due to its strong spin–orbit coupling (SOC), which produces Mott insulating states and anomalous physical behaviors. In this paper, the microscopic magnetism of Sr₂IrO₄ is studied with electron spin resonance (ESR) measurements. The Lande factor g of the ferromagnetic resonance signal of Sr₂IrO₄ shows anomalous behavior compared to typical ferromagnets. It gradually decreases, and the corresponding resonance field H_r increases, with decreasing temperature. The various physical parameters. including the saturated magnetic field H_s derived from M-H, H_r, ΔH_pp, the g factor and the intensity I extracted from ESR spectra, are analyzed in detail. Eventually, it is revealed that the anomalous behavior of the g-factor is induced by in-plane Dzyaloshinsky–Moriya interaction (DMI) rather than the SOC effect. Full article

In this study, we give a thorough evaluation of the structural, magnetic, and magnetocaloric properties in iron-rich PrFe${}_{11}$Ti intermetallic alloy with ThMn${}_{12}$-type structure using a combination of experimental and theoretical analysis. X-ray diffraction coupled with Rietveld refinement was used to characterize the structure, which revealed a unique tetragonal crystal structure with $I4/mmm$ space group. The $8i$ site was identified as the preferred site for the Ti atom. This finding was confirmed by various techniques, including XRD, DFT, and Mössbauer spectrometry. Magnetic properties were studied through intrinsic magnetic measurements and magnetocaloric effect analysis. Mössbauer spectroscopy was employed to probe the local magnetic environment and for further characterization of the material’s magnetic properties. The experimental results were complemented by theoretical calculations based on density functional theory (DFT). A promising magnetocaloric effect is observed, with a significant maximum magnetic entropy ($-\Delta S_M^{\max }$ = 2.5 J·kg${}^{-1}$·K${}^{-1}$) and a relative cooling power about 70 J·kg${}^{-1}$ under low magnetic field change ${\mu }_0\Delta H$ = 1.5 T. Overall, our results provide a deeper understanding of the structural and magnetic properties of the material under study and demonstrate the effectiveness of the combined experimental and theoretical approach in the investigation of complex materials. The insights gained from this study could have implications for the development of advanced magnetic materials with enhanced properties for potential magnetic applications. Full article

The hexacoordinate Co(II) complex [Co(neo)₂(cin)][BPh₄]·½Me₂CO (1·½Me₂CO) containing trans-cinnamic acid (Hcin) and neocuproine (neo) was prepared. The compound 1·½Me₂CO was characterized via single-crystal X-ray analysis, FT-IR spectroscopy, and magnetic measurements. The coordination polyhedron of the complex cation adopts a deformed octahedron shape, and cinnamate exhibits a bidentate mode of coordination, which is unusual for mononuclear Co(II) cinnamate complexes. The analysis of DC magnetic measurements with zero-field splitting (ZFS) spin Hamiltonian revealed large magnetic anisotropy defined by the axial ZFS parameter D = +53.2 cm⁻¹. AC susceptibility measurements revealed the slow relaxation of magnetization under the applied field; thus, 1·½Me₂CO behaves as a field-induced single-molecule magnet. The analysis of magnetic properties was also supported by CASSCF/NEVPT2 calculations. Full article

A new method for obtaining nanosized particles of iron oxides using porous silica gel is proposed. In situ magnetometry was used to study the reduction of hematite deposited on silica gel during the thermolysis of glucose. The formed magnetite and maghemite obtained by subsequent oxidation of the magnetite were studied using X-ray diffraction and Mossbauer spectroscopy. It was shown that both the size of the oxide particles and the phase composition significantly depended on the porous structure of the silica gel. In particular, the formation of superparamagnetic maghemite particles on silica gels with pore sizes of 30, 15 and 10 nm was demonstrated. Full article

In this work, the possibility of fabricating composite magneto-optical ceramics by electrophoretic deposition (EPD) of nanopowders and high-temperature vacuum sintering of the compacts was investigated. Holmium oxide was chosen as a magneto-optical material for the study because of its transparency in the mid-IR range. Nanopowders of magneto-optical (Ho_0.95La_0.05)₂O₃ (HoLa) material were made by self-propagating high-temperature synthesis. Nanopowders of (Y_0.9La_0.1)₂O₃ (YLa) were made by laser synthesis for an inactive matrix. The process of formation of one- and two-layer compacts by EPD of the nanopowders from alcohol suspensions was studied in detail. Acetylacetone was shown to be a good dispersant to obtain alcohol suspensions of the nanopowders, characterized by high zeta potential values (+29–+80 mV), and to carry out a stable EPD process. One-layer compacts were made from the HoLa and YLa nanopowders with a density of 30–43%. It was found out that the introduction of polyvinyl butyral (PVB) into the suspension leads to a decrease in the mass and thickness of the green bodies deposited, but does not significantly affect their density. The possibility of making two-layer (YLa/HoLa) compacts with a thickness of up to 2.6 mm and a density of up to 46% was demonstrated. Sintering such compacts in a vacuum at a temperature of 1750 °C for 10 h leads to the formation of ceramics with a homogeneous boundary between the YLa/HoLa layers and a thickness of the interdiffused ion layer of about 30 μm. Full article

The involvement of spin symmetry in the evaluation of zero-field energy levels in polynuclear transition metal and lanthanide complexes facilitates the division of the large-scale Hamiltonian matrix referring to isotropic exchange. This method is based on the use of an irreducible tensor approach. This allows for the fitting of the experimental data of magnetic susceptibility and magnetization in a reasonable time for relatively large clusters for any coupling path. Several examples represented by catena-[A_N} and cyclo-[A_N] systems were modeled. Magnetic data for 20 actually existing endohedral clusters were analyzed and interpreted. Full article

A mononuclear Ni(II) complex, [Ni(HL1)₂], (1) and a novel tetranuclear heterometal Mn-Ni complex, [Mn₃Ni(L1)₄Cl₂(EtOH)₂], (2) [H₂L1 = N-(2-hydroxymethylphenyl)salicylideneimine], have been synthesized and characterized via X-ray crystal structure analyses, infrared spectra, and elemental analyses. The structure analyses revealed that the tridentate ligand, H₂L1, coordinates in a facial mode for Ni and a mer mode for Mn, respectively. Complex 2 includes Mn(II)Mn(III)₂Ni(II) tetranuclear metal core bridged by μ-phenoxo and μ-alkoxo oxygens. Magnetic measurements for 2 indicate that weak ferromagnetic interactions (J_{Mn(III)Ni(II)} = 2.23, J_{Mn(III)Mn(II)} = 0.46, J_Mn(II)Ni(II) = 1.78, and J_{Mn(III)Mn(III)} = 0.58 cm⁻¹) dominate in the tetranuclear core. Additionally, in alternating current (AC) magnetic measurements, frequency-dependent out-of-phase responses were observed. Full article

A wide class of materials with different crystal and electronic structures including quasi-2D unconventional superconductors, such as cuprates, nickelates, ferropnictides/chalcogenides, ruthenate Sr${}_2$RuO${}_4$, and 3D systems, such as manganites RMnO${}_3$, ferrates (CaSr)FeO${}_3$, nickelates RNiO${}_3$, silver oxide AgO, are based on Jahn–Teller $3d$ and $4d$ ions. These unusual materials, called Jahn–Teller (JT) magnets, are characterized by an extremely rich variety of phase states, spanning from non-magnetic and magnetic insulators to unusual metallic and superconducting states. The unconventional properties of JT magnets can be attributed to the instability of their highly symmetric Jahn–Teller “progenitors” with the ground orbital E-state with repect to charge transfer, anti-Jahn–Teller d-d disproportionation, and the formation of a system of effective local composite spin–singlet or spin–triplet, electronic, or hole S-type bosons moving in a non-magnetic or magnetic lattice. We consider specific features of the anti-JT-disproportionation reaction, properties of the electron–hole dimers, possible phase states and effective Hamiltonians for single- and two-band JT magnets, concluding with a short overview of physical properties for actual JT magnets. Full article

Here, we examine the conductance changes associated with the change in spin state in a variety of different structures, using the example of the spin crossover complex [Fe(H₂B(pz)₂)₂(bipy)] (pz = (pyrazol-1-yl)-borate and bipy = 2,2′-bipyridine) and [Fe(Htrz)₂(trz)](BF₄)] (Htrz = 1H-1,2,4-triazole) thin films. This conductance change is highly variable depending on the mechanism driving the change in spin state, the substrate, and the device geometry. Simply stated, the choice of spin crossover complex used to build a device is not the only factor in determining the change in conductance with the change in spin state. Full article