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In this paper, we present the calculation results of the electronic structure and optical spectrum and an experimental study of the optical properties of Heusler alloys Mn2 –xFe1 +xAl (x = –0.5, 0, 0.5, 1). An anomalous for metallic systems behavior of the optical conductivity of alloys in the IR region of the spectrum was found: the absence of Drude growth and a high level of interband absorption. This behavior is shown to be determined by the features of the electronic structure: the Fermi level is located in the region of high density of states that is formed by the d states of Mn and Fe. [ABSTRACT FROM AUTHOR]

This paper presents electronic spectrum calculations and a study of the optical properties of the binary compounds Mn70Al30 and Mn80Al20 with the β-Mn structure. The energy dependences of the calculated density of states, with high values at the Fermi level, are determined by broad bands formed by manganese 3d states. The calculated electronic structures are used to analyze measured optical conductivity spectra of the alloys in the quantum light absorption range. From their optical properties in the infrared spectral region, we evaluate a number of characteristics of conduction electrons. [ABSTRACT FROM AUTHOR]

Theoretical calculations of the electronic structure and measurements of optical properties of the Heusler alloy Mn1.5Fe1.5Al have been performed. The density functional theory based optimized β-Mn-type crystal structure is reported for the first time for Mn1.5Fe1.5Al. An anomalous for metals behavior of the optical conductivity of the alloy in the infrared (IR) spectral region was found, i.e., the absence of the Drude rise and a high level of interband absorption. Such features of the optical spectrum indicate a complex structure of the band spectrum and a high density of states in the vicinity and at the Fermi level. The features on the optical conductivity curve are related to certain interband electron transitions. [ABSTRACT FROM AUTHOR]

We have investigated the structural, optical, and magnetic properties of D03 Fe3Al alloys along with the electronic structure calculations. X-ray diffraction patterns confirm the single-phase cubic structure with a symmetry for the arc-melted samples. In the field dependence of magnetic data, ferromagnetic behavior is witnessed down to 2 K from room temperature. The electronic structure calculation corroborates the experimental observation of ferromagnetism in this alloy. Further, optical conductivity data in excellent agreement with the electronic structure calculations confirmed that electronic transitions are predominant by the 3d states of Fe. [ABSTRACT FROM AUTHOR]

Electronic, structural, optical, and magnetic properties of the Mn100−xGex alloys for x = 20, 25, and 30 are investigated near a tetragonal–orthorhombic structural phase transition. In the electronic structure calculations, the ferrimagnetic ground state is found which is in excellent agreement with the experimental observation of magnetic properties. The calculations reveal that the main contribution to the optical absorption is associated with the electronic transitions in the system of 3d manganese bands, these states significantly change near the Fermi energy. The optical conductivity of the alloys is also transformed with an increase of the low‐energy absorption values near structural phase transition due to the enhanced electronic transitions. Among different compositions of the studied Mn–Ge, the highest magnetization is observed for Mn70Ge30 whereas highest coercivity is observed for the Mn75Ge25 alloy. High coercivity can be ascribed to the highest magneto‐crystalline anisotropy of the sample whereas high magnetization of Mn70Ge30 can be due to the presence of a hexagonal ferromagnetic phase with higher magnetization. The effect of Mn–Ge composition on the structural phase transition and its relationship with the electronic structure, optical, and magnetic properties may allow for better designing of new Heusler alloys for various customized applications. [ABSTRACT FROM AUTHOR]

Herein, we report unusual magnetic behavior in arc melted bulk stoichiometric Fe 3 Al alloy with a D0 3 structure. The temperature variation in the magnetization measurements revealed two transitions, i.e. one at ∼763 K and another at ∼830 K. Below 763 K, it exhibits ferromagnetic ordering and the nature of the transition is second order. However, the second transition is more complex and detailed analysis of the magnetic data suggested the coexistence of ferromagnetic and paramagnetic phases (two-phase: α + D0 3 /α + B2) and structural transitions triggered by temperature. We observed dual peaks in the magnetic entropy change curve, in accordance with the magnetization results, which corroborate the occurrence of a two-phase system. We believe that the concurrent magnetic ordering and the complex two-phase are associated with the evolution of short-range ordered magnetic clusters having a magnetic moment of ∼10 3 μ B in the host matrix. A cluster hypothesis is proposed to explain the observed intricate magnetic behavior of this alloy at high temperature. The estimated critical exponents using a modified Arrott plot, Kouvel-Fisher plot and critical isotherm analysis lie in between the 3D-Heisenberg and 3D-Ising model, indicating a short-range interaction and magnetic inhomogeneity, which again are consistent with the magnetization results. The obtained critical exponents follow the universal scaling behavior, which indicates the renormalization of interactions around the magnetic ordering transition (T C ). Despite the obvious larger thermal entropy at very high temperature, our synthesized Fe 3 Al alloy showed enhanced magnetic entropy changes. The obtained magnetic entropy change for binary Fe 3 Al alloy shows twice the value of that of other binary/ternary Fe-based alloys.

Oxide based dilute magnetic semiconductor materials have been of great interest over the years due to their potential use in spintronic devices. However, the variations in the magnetic behavior of the materials have raised concerns regarding the origin of ferromagnetic properties which still needs to be explored. Manipulation of magnetic behavior in oxide based dilute magnetic semiconductors has become a challenge due to the interplay of intrinsic defects present in the material. TiO 2 nanocrystals have been studied largely due to their challenging optical and magnetic properties. The present investigation studies in detail the structural, morphological, optical and magnetic behavior of non-magnetic element (Cu and Zn) doped TiO 2 , synthesized via a simple sol-gel technique. X-ray diffraction patterns and Raman spectra confirm the anatase phase and high resolution transmission electron microscopic results clearly indicate the formation of highly crystalline nanocrystals in all the samples with particle size ranging from 5-15 nm. Energy dispersive X-ray fluorescence spectroscopic studies reveal the compositional homogeneity of all the investigated samples. The presence of functional groups and molecular interactions were identified by Fourier transform infrared spectroscopy. Optical properties were studied through UV-visible and photoluminescence spectroscopy from which a significant reduction in band gap in Cu-doped TiO 2 nanocrystals was found. X-ray photoelectron spectra confirm the presence of Ti 3+ , Cu 2+ , Cu + and Zn 2+ in Cu and Zn-doped TiO 2 samples. The concept of bound magnetic polarons associated with the vacancy defects at both Ti, Cu, Zn and oxygen sites is used to explain the induced weak ferromagnetic behavior in undoped, Cu and Zn-doped TiO 2 at room temperature. The overlapping of bound magnetic polarons could be the source of ferromagnetism irrespective of the non-magnetic nature of the dopant ion. The concentration of bound magnetic polarons is estimated using a Langevin fit and a detailed understanding of the variation of defect mediated magnetic properties is established with the help of PL analysis. A significant reduction in bandgap along with enhanced magnetization observed in the Cu-doped TiO 2 material makes it suitable as a potential candidate for spintronics and magneto-optics applications. Room temperature magnetic properties of the Zn doped sample show a diamagnetic tail which is explained based on the defect centers and oxidation states of dopant ions present in the sample which is further verified with the help of XPS results., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)