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The [Gd[sub.8](opch)[sub.8](CO[sub.3])[sub.4](H[sub.2]O)[sub.8]]·4H[sub.2]O·10MeCN coordination cluster (1) crystallises in P1¯. The Gd[sub.8] core is held together by four bridging carbonates derived from atmospheric CO[sub.2] as well as the carboxyhydrazonyl oxygens of the 2-hydroxy-3-methoxybenzylidenepyrazine-2-carbohydrazide (H[sub.2]opch) Schiff base ligands. The magnetic measurements show that the Gd[sup.III] ions are effectively uncoupled as seen from the low Weiss constant of 0.05 K needed to fit the inverse susceptibility to the Curie–Weiss law. Furthermore, the magnetisation data are consistent with the Brillouin function for eight independent Gd[sup.III] ions. These features lead to a magnetocaloric effect with a high efficiency which is 89% of the theoretical maximum value.

In this work, we explore the impacts of charge doping on the magnetism of a Cr[sub.2]Ge[sub.2]Te[sub.6] monolayer using first-principles calculations. Our results reveal that doping with 0.3 electrons per unit cell can enhance the ferromagnetic exchange constant in a Cr[sub.2]Ge[sub.2]Te[sub.6] monolayer from 6.874 meV to 10.202 meV, which is accompanied by an increase in the Curie temperature from ~85 K to ~123 K. The enhanced ratio of the Curie temperature is up to 44.96%, even higher than that caused by surface functionalization on monolayer Cr[sub.2]Ge[sub.2]Te[sub.6], manifesting the effectiveness of charge doping by improving the magnetic stability of 2D magnets. This remarkable enhancement in the ferromagnetic exchange constant and Curie temperature can be attributed to the increase in the magnetic moment on the Te atom, enlarged Cr-Te-Cr bond angle, reduced Cr-Te distance, and the significant increase in super-exchange coupling between Cr and Te atoms. These results demonstrate that charge doping is a promising route to improve the magnetic stability of 2D magnets, which is beneficial to overcome the obstacles in the application of 2D magnets in spintronics.

MnSb[sub.2]Te[sub.4] has a similar structure to an emerging material, MnBi[sub.2]Te[sub.4]. According to earlier theoretical studies, the formation energy of Mn antisite defects in MnSb[sub.2]Te[sub.4] is negative, suggesting its inherent instability. This is clearly in contrast to the successful synthesis of experimental samples of MnSb[sub.2]Te[sub.4]. Here, the growth environment of MnSb[sub.2]Te[sub.4] and the intrinsic defects are correspondingly investigated. We find that the Mn antisite defect is the most stable defect in the system, and a Mn-rich growth environment favors its formation. The thermodynamic equilibrium concentrations of the Mn antisite defects could be as high as 15% under Mn-poor conditions and 31% under Mn-rich conditions. It is also found that Mn antisite defects prefer a uniform distribution. In addition, the Mn antisite defects can modulate the interlayer magnetic coupling in MnSb[sub.2]Te[sub.4], leading to a transition from the ideal antiferromagnetic ground state to a ferromagnetic state. The ferromagnetic coupling effect can be further enhanced by controlling the defect concentration.

We report on the far-infrared, temperature-dependent optical properties of a CrI[sub.3] transition metal halide single crystal, a van der Waals ferromagnet (FM) with a Curie temperature of 61 K. In addition to the expected phonon modes determined by the crystalline symmetry, the optical reflectance and transmittance spectra of CrI[sub.3] single crystals show many other excitations as a function of temperature as a consequence of the combination of a strong lattice anharmonicity and spin–phonon coupling. This complex vibrational spectrum highlights the presence of entangled interactions among the different degrees of freedom in CrI[sub.3].

High-quality NdCrSb[sub.3] single crystals are grown using a Sn-flux method, for electronic transport and magnetic structure study. Ferromagnetic ordering of the Nd[sup.3+] and Cr[sup.3+] magnetic sublattices are observed at different temperatures and along different crystallographic axes. Due to the Dzyaloshinskii-Moriya interaction between the two magnetic sublattices, the Cr moments rotate from the b axis to the a axis upon cooling, resulting in a spin reorientation (SR) transition. The SR transition is reflected by the temperature-dependent magnetization curves, e.g., the Cr moments rotate from the b axis to the a axis with cooling from 20 to 9 K, leading to a decrease in the b-axis magnetization f and an increase in the a-axis magnetization. Our elastic neutron scattering along the a axis shows decreasing intensity of magnetic (300) peak upon cooling from 20 K, supporting the SR transition. Although the magnetization of two magnetic sublattices favours different crystallographic axes and shows significant anisotropy in magnetic and transport behaviours, their moments are all aligned to the field direction at sufficiently large fields (30 T). Moreover, the magnetic structure within the SR transition region is relatively fragile, which results in negative magnetoresistance by applying magnetic fields along either a or b axis. The metallic NdCrSb[sub.3] single crystal with two ferromagnetic sublattices is an ideal system to study the magnetic interactions, as well as their influences on the electronic transport properties.

Iron niobates, pure and substituted with copper (Fe[sub.1−x]Cu[sub.x]NbO[sub.4] 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 Cu[sup.2+] ions into the FeNbO[sub.4] structure. The pure FeNbO[sub.4] 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[sub.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 Cu[sup.2+]-O-Fe[sup.3+] chains and the formation of bound magnetic polarons in the oxygen vacancies.

In ferromagnetic semiconductors, the coupling of magnetic ordering with semiconductor character accelerates the quantum computing. The structural stability, Curie temperature (T[sub.c]), spin polarization, half magnetic ferromagnetism and transport properties of ZnX[sub.2]Se[sub.4] (X = Ti, V, Cr) chalcogenides for spintronic and thermoelectric applications are studied here by density functional theory (DFT). The highest value of T[sub.c] is perceived for ZnCr[sub.2]Se[sub.4]. The band structures in both spin channels confirmed half metallic ferromagnetic behavior, which is approved by integer magnetic moments (2, 3, 4) μ[sub.B] of Ti, V and Cr based spinels. The HM behavior is further measured by computing crystal field energy ΔE[sub.crystal], exchange energies Δ[sub.x](d), Δ[sub.x] (pd) and exchange constants (N[sub.o]α and N[sub.o]β). The thermoelectric properties are addressed in terms of electrical conductivity, thermal conductivity, Seebeck coefficient and power factor in within a temperature range 0-400 K. The positive Seebeck coefficient shows p-type character and the PF is highest for ZnTi2Se4 (1.2 × 10[sup.11] W/mK[sup.2]) among studied compounds.

The results of a theoretical study of the Fe.sub.3SiTe.sub.2 compound, belonging to a promising class of the van der Waals systems with high Curie temperature and gigantic magnetoresistance, are presented. It is found out that Fe.sub.3SiTe.sub.2 represents a ferromagnetic metal characterized by high spin-polarization values at the Fermi level. It is shown that the charge transport occurs due to a contribution from the spin-down electrons and is formed prevailingly in the plane of five-layer blocks.

While SmB[sub.6] attracts attention as a possible topological Kondo insulator, EuB[sub.6] is known to host magnetic polarons that give rise to large magnetoresistive effects above its ferromagnetic order transition. Here, we investigate single crystals of Sm[sub.1−x]Eu[sub.x]B[sub.6] by magnetic and magnetotransport measurements to explore a possible interplay of these two intriguing phenomena, with a focus on the Eu-rich substitutions. Sm[sub.0.01]Eu[sub.0.99]B[sub.6] exhibits generally similar behavior as EuB[sub.6]. Interestingly, Sm[sub.0.05]Eu[sub.0.95]B[sub.6] combines a global antiferromagnetic order with local polaron formation. A pronounced hysteresis is found in the magnetoresistance of Sm[sub.0.1]Eu[sub.0.9]B[sub.6] at low temperature (T= 1.9 K) and applied magnetic fields between 2.3 and 3.6 T. The latter is in agreement with a phenomenological model that predicts the stabilization of ferromagnetic polarons with an increasing magnetic field within materials with a global antiferromagnetic order.

The synthesis of polycrystalline TiFe[sub.2]Sn samples by a route including arc melting and spark plasma sintering with Hf, Y, and In substitutions at the Ti and Sn sites is investigated. For a reduced amount of substitution, around 2 at%, the samples are single phase, while for increased amounts, secondary phases segregate. As is characteristic of these compounds, the Fe-Ti atomic disorder generates a weak ferromagnetic ordering, which is also influenced by the type of substitutional atoms and the secondary phases in the samples with a higher Hf content. The Seebeck coefficient values show an increase for Ti[sub.0.98]Hf[sub.0.02]Fe[sub.2]Sn and for samples with an adjusted Sn content, resulting in slightly increased power factor values. These values reach a maximum for Ti[sub.0.98]Hf[sub.0.02]Fe[sub.2]Sn at approximately 300 K and for TiFe[sub.2]Sn[sub.1.05] at approximately 325 K, namely, 2.69 × 10⁻[sup.4] Wm[sup.−1]K[sup.−2] and 2.52 × 10⁻[sup.4] Wm[sup.−1]K[sup.−2], respectively. The thermal conductivity of all the samples with substitutions increases with respect to the pristine sample. The highest figure of merit value of 0.016 is also obtained for Ti[sub.0.98]Hf[sub.0.02]Fe[sub.2]Sn at 325 K.