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• Structure-properties (magnetic, electrical and thermal) relationship of Mn3Al alloy. • Observation of weak ferromagnetism buried in an antiferromagnet. • High value of electronic heat capacity. • Disordered system with strong frustration. Numerous interesting features of antiferromagnets open up the possibility of designing new antiferromagnetic materials that can be useful for spintronic device applications. Here we present the structural, magnetic, thermal and electrical transport properties of polycrystalline Mn 3 Al alloys prepared by arc melting. Rietveld refinement of the room temperature X-Ray diffraction patterns reveals that the arc-melted Mn 3 Al crystallizes in a β Mn phase (space group 213). Detailed analysis of the magnetic data suggests for a dominant antiferromagnetic ordering. However, an in-homogenous magnetic disorder is observed in the system having a weak ferromagnetic phase in the antiferromagnetic host. In spite of the strong spin fluctuations in this system, the signature of spin glass-like nature in these alloys are not observed as probed by the frequency-dependent AC-Susceptibility measurements. Furthermore, the heat capacity was insensitive to the applied field of 3 Tesla with a negligible magnetic contribution suggesting a large electronic contribution to the heat capacity in these alloys. This work provides a useful insight into the tunable physical properties of the Heusler alloys for exploring antiferromagnetic based spintronic applications. [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]

• Detailed theoretical and experimental study of arc melted Mn 2 FeAl alloy with a β-Mn structure. • Phase stability of β-Mn structure is verified by comparing the total energies of the other probable Heusler type structures. • With volume expansion, β-Mn structure of Mn 2 FeAl becomes the lowest ground state configuration. • Experimental realization of spin glass features in a frustrated antiferromagnet. The synthesized Mn 2 FeAl alloys crystallize in a geometrically frustrated cubic β-Mn structure (space group: P4 1 32) with an antiferromagnetic ordering whereas the previous theoretical findings suggest for a Heusler structure (L2 1 : regular and X: inverse). The experimental stability of the structure is verified by electronic structure calculations performed for various arrangements of Mn, Fe and Al atoms in the β-Mn-type crystal structure. When compared the energy of the β-Mn structure with the energy of L2 1 and X type structures, it is found that for an expansion of the lattice volume β-Mn structure becomes more preferable in total energy than L2 1 and X-type structures. The calculated theoretical equilibrium lattice parameter value for the β-Mn 2 FeAl is within the accuracy of the experimental value obtained in this work. Additional DFT + U calculations for the optimized crystal structure of the β-Mn 2 FeAl revealed that the electronic correlations in the Mn ions result in the increased total magnetic moment. In the X type structure, Mn 2 FeAl is a half metal, whereas the disordered arrangement of atoms in the β-Mn structure leads to the closure of the semiconductor gap. The β- Mn 2 FeAl alloys exhibit antiferromagnetic ordering (T N ≈ 42 K), which is in excellent agreement with our electronic structure calculations. The detailed analysis of the magnetic and heat capacity measurements suggests a short-range magnetic ordering in the Mn 2 FeAl alloys. Owing to the strong antiferromagnetic spin fluctuation caused by the geometric frustration in β-Mn, a large enhancement in the electronic heat capacity is noticed. Mn 2 FeAl shows the characteristic features of spin glass as verified from the frequency dependent AC susceptibility analysis using critical power law and Vogel-Fulcher law. To the best of our knowledge, this is the first ever report on the theoretically predicted lowest ground state configuration for Mn 2 FeAl with a β-Mn structure and the experimental realization of spin glass features in this geometrically frustrated antiferromagnet. [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]

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]

• Mn 1.5 Fe 1.5 Al alloy with a β-Mn structure exhibits canonical spin-glass behaviour. • Large frustration parameters indicting high degree of frustration is measured. • Hierarchical model of the spin-glass magnetic relaxation is observed. • Unidirectional exchange bias effect and memory effect are also observed. Magnetic properties of magnetically frustrated polycrystalline Mn 1.5 Fe 1.5 Al Heusler type alloy with a β-Mn structure were systematically studied using dc magnetization, ac susceptibility, magnetic relaxation and magnetic memory effect measurements to understand its magnetic ground state. The Mn 1.5 Fe 1.5 Al alloy system exhibits a sharp peak at low temperature around 34.5 K with strong antiferromagnetic correlations (θ CW ∼ −639 K) and a high degree of frustration (f p ∼ 18.7) which suggest the presence of competing magnetic interactions. Despite of strong antiferromagnetic correlations, this peak has spin-glass character as confirmed by the observations of bifurcation of the zero-field-cooled and field-cooled magnetization curves below the irreversibility temperature, field dependent shift of the irreversibility temperature, unidirectional exchange bias effect on the field-cooled M-H hysteresis loop, exponential decay of the temperature variation of remanence and coercivity, frequency dependent shift of the spin glass freezing temperature (T f) as per the dynamic scaling laws given by the critical slowing down model and Vogel-Fulcher law, magnetic relaxation and magnetic memory effect below T f. The observation of a clear asymmetric response with respect to the temperature cycling in the magnetic relaxation measurements validates the hierarchical model of the spin-glass magnetic relaxation in Mn 1.5 Fe 1.5 Al alloy. Since the behaviour exhibited by the Mn 1.5 Fe 1.5 Al alloy has perfect similarity with the well-known atomic spin glasses like CuMn, AuFe, therefore, it may be considered as canonical spin-glass system. [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 studied the structural, magnetic, dielectric and impedance properties of the Sm 1-x Bi x Fe 1-y Mn y O 3 [SmFeO 3 (SFO), Sm 0.9 Bi 0.1 FeO 3 (SBFO), Sm 0.9 Bi 0.1 Fe 0.9 Mn 0.1 O 3 (SBFMO)] polycrystalline samples synthesized by solid-state reaction method. Rietveld refinement of room temperature (RT) powder x-ray diffraction pattern confirms the orthorhombic crystal structure with Pnma/Pbnm space group. The average particle size of Bi doped and co-doped (Bi–Mn) samples determined from SEM analysis are 5.6 μm and 5.2 μm, respectively. Room temperature field-dependent magnetization increases, suggesting the presence of magnetic contribution due to the Rare earth-Fe ion interaction which persists even at RT. However, with co-doping of Bi and Mn, a decrease in magnetization is observed, which corresponds to the dilution of Fe3+-Fe3+ interactions due to the presence of Mn3+ ions. The observed values of magnetization at 90 kOe for Bi doped sample is (2.87 emu/g) approximately two times and for codoped (0.7 emu/g) sample is nearly half of that of pristine sample (1.51 emu/g). Dielectric measurements as a function of frequency/temperature and impedance analysis using equivalent circuit model reveal grain and grain boundary contributions of SBFO (at high temperature) and SBFMO (for all temperature) samples towards the electrical properties indicating the electrically heterogeneous nature of these samples. However, for SFO sample grain contribution is dominant. Observed value of dielectric constant varies from ~103-104 with Bi–Mn doping. The conduction mechanism of the studied samples has been explained by considering Jonscher power law. Arrhenius law fitting of AC conductivity data manifests two types of conduction mechanisms in these samples. The depressing nature of the semicircular arc observed in the Nyquist plot of all the samples indicates the presence of a non-Debye type of relaxation. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.1134/S0020168523330014 [ABSTRACT FROM AUTHOR]