We report on the magnetism of amorphous SiO₂–Al₂O₃–CaO–MgO–Fe₂O₃–K₂O–MnO:CA (CA—activated carbon) aluminosilicate glasses prepared by a fusion-quenching method. Fourier transform infrared and Raman spectroscopy show that a Fe²⁺ lattice modifier in the glass structures induces depolymerization, strongly influencing the magnetic transitions. Room temperature magnetization measurements of the CA-glasses show a different magnetic behavior, such as speromagnetism, asperomagnetism, and weak ferromagnetism. Mössbauer spectroscopy analyses at room temperature reveal that iron changes valence from Fe³⁺ → Fe²⁺ with increasing CA content. This Fe³⁺ → Fe²⁺ suggests that asperomagnetism and weak ferromagnetism behavior are triggered by Fe²⁺–O–Fe³⁺ superexchange coupling in short-range structures of aluminosilicate glasses. A model for the aluminosilicate glass structures is proposed to explain the different magnetic regimes.

Iron niobates, pure and substituted with copper (Fe_1−xCu_xNbO₄ with x = 0–0.15), were prepared by the solid-state method and characterized by X-ray diffraction, Raman spectroscopy, and magnetic measurements. The results of the structural characterizations revealed the high solubility of Cu ions in the structure and better structural stability compared to the pure sample. The analysis of the magnetic properties showed that the antiferromagnetic–ferromagnetic transition was caused by the insertion of Cu²⁺ ions into the FeNbO₄ structure. The pure FeNbO₄ structure presented an antiferromagnetic ordering state, with a Néel temperature of approximately 36.81K. The increase in substitution promoted a change in the magnetic ordering, with the state passing to a weak ferromagnetic order with a transition temperature (T_c) higher than the ambient temperature. The origin of the ferromagnetic ordering could be attributed to the increase in super-exchange interactions between Fe/Cu ions in the Cu²⁺-O-Fe³⁺ chains and the formation of bound magnetic polarons in the oxygen vacancies.

In the present work, we conducted a comprehensive study using multiple experimental techniques to elucidate the structural, charge-state, vibrational, and magnetic properties of the quasi-one-dimensional spin chain system Fe_0.75Cu_0.25NbO₄. We found that substituting Fe³⁺ (3d⁵, s = 5/2) with Cu²⁺ (3d⁹, s = 1/2) induces significant changes in the lattice parameters, mixed valence states of Cu (Cu²⁺ and Cu¹⁺), and oxygen vacancies, as well as a ferrimagnetic (FiM) ordered state at room temperature. The FiM state is supported by double-exchange interactions between Fe³⁺ and Cu²⁺, mediated by oxygen, which highlight the magnetization mechanism and help describe the complex magnetic interactions among the Fe ions in this compound. We examined the temperature dependence of the magnetic order and, notably, observed a transition from ferrimagnetic to antiferromagnetic (FiM to AFM) at T = 38.4 K. ⁵⁷Fe Mössbauer spectroscopy indicates two Fe species, both in the trivalent state: one arising from Fe ions in a distorted octahedral configuration that interact with octahedrally substituted Cu polyhedra, favoring a FiM state among Fe ions with an ordering temperature above 300 K, and a second species associated with conventional Fe–Fe interactions that lead to the ordinary AFM state at 38 K. The magnetic transition was confirmed by the M vs T and ΔS _M vs T curves. Furthermore, Raman spectroscopy captures this magnetic transition and reveals clear spin-phonon coupling.

The structural, vibrational, electronic, optical, and magnetic properties of triclinic Cu₃Nb₂O₈ were investigated through a combined experimental and theoretical approach. Synchrotron X-ray diffraction confirmed the centrosymmetric P1̅ structure, while Raman and infrared spectroscopy enabled the identification of the vibrational modes, supported by lattice-dynamics calculations. Density functional theory calculations indicated that the electronic states near the conduction band minimum are mainly associated with Cu 3d orbitals, whereas the valence band is predominantly composed of O 2p states. Magnetic susceptibility measurements revealed two antiferromagnetic transitions at T ₁ = 26.09 K and T ₂ = 24.15 K. Temperature-dependent Raman analyses evidenced anomalous phonon behavior between 20 and 60 K, indicating spin-phonon interactions associated with the magnetic ordering process. In addition, magnetocaloric measurements exhibited a magnetic entropy variation centered near the Néel temperature, reinforcing the presence of magnetoelastic coupling in Cu₃Nb₂O₈. These results provide a comprehensive description of the interplay between lattice dynamics, electronic structure, and magnetic ordering in this copper orthoniobate system.