Senthur Pandi Rajasabai

This work explores the influence of Co substitution in place of Mn and Ni on the structural, thermal, and magnetic properties of Mn45Ni35Sn15Co5 (C1) and Mn50Ni30Sn15Co5 (C2) samples. The samples were prepared using the green compact method, annealed in a vacuum-sealed quartz tube at 950 ◦C for 96 h, and quenched in cold water. X-ray diffraction analysis confirmed the presence of Mn2NiSn with the XA (inverse Heusler) structure as the major phase. Differential scanning calorimetry revealed possible magnetic transitions at higher temperature regions. Magnetic parameters, including the spin-wave stiffness, exchange stiffness and magneto crystalline anisotropy were estimated using modified Bloch's law and the law of approach to saturation. The isothermal magnetization analysis revealed that the samples are soft ferromagnetic in nature. Co substitution of Mn increases the magnetization, spin-wave stiffness and exchange stiffness. Whereas Co substitution of Ni gives rise to antiferromagnetic sub lattices and frustrated magnetic state.

Polycrystalline CoMnAl alloy was synthesised by vacuum arc melting followed by annealing to investigate its structural, magnetic, and magnetocaloric properties. PowderX-ray diffraction combined with Rietveld refinement, using the NiMnSb-type half-Heusler structural model, confirmed the formation of a single-phase cubic structure with space group 𝐹 ̄43𝑚 (No. 216). The refined lattice parameter was determined to be 𝑎 = 5.789(3) Å, with good agreement between the experimental and calculated diffraction profiles. Room-temperature magnetic measurements revealed soft ferromagnetic behaviour, with a saturation magnetisation of approximately 118 Am2 kg-1, a low coercive field of 8.6 Oe, and an effective magnetic anisotropy constant of 28.5 kJm-3. Temperature-dependent magnetisation measurements revealed a continuous ferromagnetic–paramagnetic transition at a Curie temperature of approximately 624 K. The temperature dependence of the magnetisation was further analysed using the modified Bloch model, from which the spin-wave stiffness constant was estimated.

Iron in its elemental form has rarely been detected in the interstellar medium despite being the most abundant refractory element. The presence of iron oxides in the interstellar medium and the recent discovery of FeC in the circumstellar envelope of IRC+10,216 suggest iron-carbon-oxygen molecules as potential interstellar species. In light of this possibility, the potential energy surface of FeC ₂ O has been investigated computationally using different levels of density functional theory calculations, yielding fourteen, seven, and twenty isomers across the quintet, triplet, and singlet electronic states, respectively. Within the examined DFT frameworks, the lowest energy isomer of FeC ₂ O is in the quintet electronic state with a linear structure. Single-point (U)CCSD(T) calculations with T ₁ diagnostics reveal considerable multireference character in certain geometries. CASSCF optimizations are performed on quintet state geometries to account for the multireference character. Various computational tools, such as adaptive natural density partitioning (AdNDP) analysis, molecular orbital (MO) analysis, and Wiberg Bond Indices (WBI), are employed to elucidate the bonding characteristics of the global minimum geometry. The spectroscopic parameters in both infrared and microwave domains have been successfully computed. The total and the partial density of states are plotted to evaluate how different atoms contribute to the electronic structure. The structural, energetic, and spectroscopic parameters presented in this work have significant implications for future astronomical research.

The structural and magnetic properties of the Co2MnAl full Heusler alloy is investigated withemphasis on disorder-driven magnetic behavior. X-ray diffraction confirms the formation of a orderedL21 cubic structure. Magnetization measurements reveal soft ferromagnetic behavior with a Curietemperature of 𝑇𝑐 ≈ 696 K. The thermal demagnetization follows modified Bloch’s law at lowtemperatures, indicating dominant spin-wave contributions. A clear deviation from Curie–Weissbehavior above 𝑇𝑐 is observed, indicating the presence of short-range ferromagnetic correlations.The existence of a finite temperature range between 𝑇𝑐 and the Griffiths temperature (𝑇𝐺 ≈ 862 K)confirms the emergence of a Griffiths-like phase. The extracted Griffiths exponent 𝜆𝐺 ≈ 0.92764suggests magnetic inhomogeneity in Co2MnAl.

Fe75Al25 alloys were synthesized using the vacuum arc melting technique and subsequently subjected to three different heat-treatment processes at 550 ◦C to study their structural and magnetic property variations. X-ray diffraction analysis confirms that all samples crystallize in the ordered D03 structure. Room-temperature magnetic properties were investigated using vibrating sample magnetometry through 𝑀–𝐻 measurements, which reveal a clear soft magnetic behavior. The Curie temperature was determined using both the temperature derivative of magnetization and Curie–Weiss fitting. Modified Bloch law analysis indicates the presence of long-range ferromagnetic ordering in the alloys. In addition, the magnetocaloric effect was evaluated under a low applied magnetic field of 0.05 T. These results demonstrate the strong correlation between heat treatment, structural ordering, and magnetic performance in Fe3Al alloys.

This study investigates the structural evolution and critical magnetic behavior of MnxNi9 (x = 1, 2, 3) intermetallic alloys synthesized via vacuum arc melting. X-ray diffraction con10firms that the alloys crystallize in the L10 tetragonal structure, with increasing lattice strain11 observed at higher Mn concentrations. Magnetic characterization reveals a distinct composition12dependent magnetic crossover: while MnNi and Mn3Ni exhibit paramagnetic behavior at room13 temperature, Mn2Ni stabilizes as a soft ferromagnet with a Curie temperature (TC) near 296K.14 Detailed critical behavior analysis of Mn2Ni using Arrott-Noakes plots and critical isotherms15 yields a critical exponent δ ≈ 3.79, suggesting magnetic interactions intermediate between Mean-16 Field and 3D-Heisenberg models. Furthermore, modified Bloch law analysis indicates complex17 spin-wave dynamics with an anomalous exponent α ≈ 0.5. The magnetocaloric entropy change18 (|ΔSM|) was calculated to be 0.0135 J kg−1K−1 for Mn2Ni under a 0.5 T field.