•Magnetic and transport properties of Mn2FeAl were studied.•Mn2FeAl is strongly frustrated antiferromagnet with Neel temperature 40 K.•Transport properties of Mn2FeAl are typical of “bad” metals.
...Experimental studies of polycrystalline Mn2FeAl revealed that it crystallizes in a primitive cubic structure of β-Mn type (space group P4132) and is an antiferromagnet with Néel temperature TN = 40 K. The alloy exhibits temperature dependence of transport properties typical for semiconductors and has abnormally high electrical resistivity (ρ ∼ 238 μΩ·cm at room temperature). High Curie-Weiss temperature ΘCW ∼ –905 K and a large value of the frustration parameter ƒ ≈ 23 points to a strong frustration of the magnetic subsystem. These experimental findings are in contrast with reported results of first-principles calculations which predicted Mn2FeAl to be half metallic ferrimagnet crystallizing in the Heusler crystal structure.
Nearly single-phase FeVSb half-Heusler alloys with fine grains were obtained by induction melting followed by mechanical alloying (MA), spark plasma sintering (SPS) and annealing process. Hf as a ...heavy element was used as dopant to present point defects aiming at decreasing the material’s thermal conductivity during phonon scattering. Thermoelectric properties of the FeV1−xHfxSb samples (0.0 ≤ x ≤ 0.3) were investigated as a function of temperature in a range from 300 to 600 K. Microstructure investigations showed that grain size decreases with increasing the level of Hf doping (x). Seebeck coefficient of the parent FeVSb compound showed negative sign which refers to n-type conduction. Interestingly, the sign has changed to positive with introducing Hf in the FeVSb lattice at different concentrations (x ≥ 0.1), which is due to one less valence electron in Hf as compared to V. The difference between the host atom (V) and the impurity atom (Hf) in terms of mass and size has resulted in a mass fluctuation and consequently a disorder scattering. The absolute value of the Seebeck coefficient |S| of the FeVSb system was measured at 110 μV/K, while the thermal conductivity value was obtained at 10.46 Wm−1K−1 near room temperature. A maximum power factor of 1.07 mWm−1 K−2 at 420 K was recorded. The thermal conductivity decreased rapidly upon Hf doping due to increased point defect scattering caused by Hf introducing to the FeVSb system. A maximum ZT value of 0.08 at 573 K for FeV0.9Hf0.1Sb was recorded in this study.
•Thermoelectric samples of FeVSb HH compound materials with fine grains have been successfully synthesized.•Hf doping was carried out to enhance the phonon scattering.•The thermal conductivity decreased by ∼54%.•ZT value of 0.08 at 573 K for the sample with x = 0.1.
•P-type FeV0.64−xNbxHf0.16Ti0.2Sb alloys are prepared by arc melting followed by induction melting.•The samples were milled in two milling regimes and then sintered with spark plasma.•Thermoelectric ...properties were studied as functions of temperature from 300 K to 800 K.•The weighted mobility, µw, and electronic quality factor, BE, were calculated.•The maximum zT value at 725 K was achieved for BM-ed FeV0.60Nb0.4Hf0.16Ti0.2Sb sample.
This work presents experimental investigations of the thermoelectric properties of p-type FeV0.64−xNbxHf0.16Ti0.2Sb half-Heusler alloys. Samples of the concerned system were prepared through sequent procedures starting with arc melting. Fine powders of the concerned samples were then obtained by mechanical alloying using two different ball milling regimes. Spark plasma sintering technique was employed for pressing the powders. The thermoelectric properties were studied as functions of temperature from 300 K to 800 K. Alloy scattering of phonons showed great contribution in the reduction of lattice thermal conductivity. High energy ball milled FeV0.39Nb0.25Hf0.16Ti0.2Sb sample possessed the lowest lattice thermal conductivity with a value of 1.81 Wm−1 K−1 at room temperature with a reduction of –82% compared with that of FeVSb. Additionally, the electrical conductivity was improved by the Nb doping leading to notable increase in the material’s power factor. As a result, a maximum power factor of 19.5 μW cm−1 K−2 was achieved at 800 K for Nb doped at x = 0.4 of the ball milled samples. The figure of merit was increased from 0.25 for FeV0.64Hf0.16Ti0.2Sb to 0.44 for FeV0.60Nb0.4Hf0.16Ti0.2Sb due to Nb doping. Which means that the figure of merit value is enhanced by –43%. The value was recorded at 725 K.
This paper presents the study of the magnetic properties and magnetocaloric effect (MCE) of the rare-earth ferrimagnetic Dy2Fe10Al7 compound. The field and temperature dependencies of the ...magnetization in the temperature range 4.2–300 K were studied in magnetic fields up to 100 kOe. The MCE was studied by direct method in magnetic fields up to 70 kOe. It was established that the sign of the MCE changes from positive to negative near the compensation temperature. It was shown from the obtained experimental results and the theoretical estimations that the temperature and field dependencies of the MCE in rare-earth ferrimagnet differ from those in ferromagnetic materials. The effective field (Heff2) determined from the values of the MCE near to the compensation temperature are in a good agreement with those reported earlier.
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•The magnetization, susceptibility, and MCE in Dy2Fe10Al7 were investigated.•The MCE was studied by direct methods.•It is shown that the exchange field value can be estimated from the MCE data.•The influence of ferrimagnetic structure on magnetocaloric effect in Dy2Fe10Al7 compound.
•Vickers method is extremely accurate to calculate the hardness value of samples.•Electrical conductivity was improved due to optimizing the carrier concentration.•A reduction in thermal conductivity ...was achieved due to point defect scattering.•Significant enhancement in thermoelectric figure of merit (zT) was achieved.•The highest zT value at 725 K was achieved for FeV0.60Nb0.4Hf0.16Ti0.2Sb sample.
Half Heusler FeVSb-based compounds are recently identified as promising thermoelectric materials for medium to high temperature range. In this research article, thermoelectric properties of half Heusler FeV1−x-y-zHfxTiyNbzSb and FeVSb samples were studied over a temperature range from 300 to 800 K. Transition heavy elements such as Hf, Ti and Nb were used as dopants to enhance the phonon scattering aiming at reducing the material’s thermal conductivity. The FeV0.24Nb0.4Hf0.16Ti0.2Sb compound showed the lowest lattice thermal conductivity (κl) with a value of (1.81 ± 0.1 Wm−1 K−1) at room temperature with a reduction of ~82% compared with that of FeVSb compound. A maximum power factor value of (9.8 ± 0.9) μW cm−1 K−2 at 800 K and figure of merit (zT) value of 0.44 were recorded at 725 K for FeV0.24Nb0.4Hf0.16Ti0.2Sb. Vickers hardness method was used to estimate the hardness of the concerned alloys by micro-hardness technique, subjected to various applied loads. All the concerned samples showed significant mechanical stability. A maximum hardness value of 19.15 ± 0.77 GPa at load of 0.98 N was obtained for the FeV0.24Nb0.4Hf0.16Ti0.2Sb compound.
We report the preparation of soft ferromagnetic spinel MFe
2
O
4
(M = Ni, Mg, Zn) nanoparticles via microwave-assisted combustion synthesis using
Citrus limon
fruit extract as a fuel. XRD, FTIR, ...Raman, and EDX studies revealed that phase pure polycrystalline NiFe
2
O
4
, MgFe
2
O
4,
and ZnFe
2
O
4
having cubic structure were formed when we introduce the desired divalent metal ion during the synthesis. TEM analysis clearly shows that NiFe
2
O
4
and MgFe
2
O
4
samples have spherical shape nanoparticles, while the ZnFe
2
O
4
sample has cube-like nanoparticles with different size distributions. The average size of NiFe
2
O
4
, MgFe
2
O
4,
and ZnFe
2
O
4
nanoparticles was found to be 10 ± 3 nm, 20 ± 2 nm, and 25 ± 4 nm, respectively. We believe that citrate present in
Citrus limon
fruit extract and nitrate ions that exist in the reaction medium can act as reductant/oxidant leads to auto-combustion and form crystallized MFe
2
O
4
nanoparticles without further high-temperature calcination. From VSM analysis, the saturation magnetization for NiFe
2
O
4
, MgFe
2
O
4,
and ZnFe
2
O
4
was found as 10.16 emu/g, 8.69 emu/g, and 4.23 emu/g, respectively. The different saturation magnetization of the MFe
2
O
4
nanoparticles has a strong correlation with the magnetic moment of divalent cations (Ni
2+
, Mg
2+
, Zn
2+
), superexchange of Fe
3+
ions between the tetrahedral (A) and the octahedral (B) sites as well as owing to particle size/morphology and impurities. This study offers a facile approach to obtain soft ferromagnetic spinel ferrite nanoparticles with tunable saturation magnetization which may find a wide spectrum of applications.
Magnetic Properties of the Y2(FexCo1 –x)17 Compounds Sinkevich, A. I.; Lyakhova, M. B.; Karpenkov, A. Yu ...
Bulletin of the Russian Academy of Sciences. Physics,
05/2024, Letnik:
88, Številka:
5
Journal Article
Recenzirano
The magnetization curves of the Y
2
(Fe
x
Co
1 –
x
)
17
compounds were measured in the temperature range of 300–923 K along easy and hard magnetization directions. The magnetization curves were ...analyzed, and the magnetocrystalline anisotropy constants
K
1, 2
of the samples were calculated. The temperature and composition dependences of the anisotropy constants
K
1, 2
and the saturation magnetization
M
s
were discussed. It was shown that, with increasing relative iron concentration in the samples, the first anisotropy constant
K
1
increases and reaches a maximum value of 5.1 × 10
5
J m
–3
at
x
= 0.29.
We have explored, computationally and experimentally, the magnetic properties of (Fe1-xCox)2B alloys. Calculations provide a good agreement with experiment in terms of the saturation magnetization ...and the magnetocrystalline anisotropy energy with some difficulty in describing Co2B, for which it is found that both full potential effects and electron correlations treated within dynamical mean field theory are of importance for a correct description. The material exhibits a uniaxial magnetic anisotropy for a range of cobalt concentrations between x=0.1 and x=0.5. A simple model for the temperature dependence of magnetic anisotropy suggests that the complicated nonmonotonic behavior is mainly due to variations in the band structure as the exchange splitting is reduced by temperature. Using density functional theory based calculations we have explored the effect of substitutionally doping the transition metal sublattice by the whole range of 5d transition metals and found that doping by Re or W elements should significantly enhance the magnetocrystalline anisotropy energy. Experimentally, W doping did not succeed in enhancing the magnetic anisotropy due to formation of other phases. On the other hand, doping by Ir and Re was successful and resulted in magnetic anisotropies that are in agreement with theoretical predictions. In particular, doping by 2.5 at. % of Re on the Fe/Co site shows a magnetocrystalline anisotropy energy which is increased by 50% compared to its parent (Fe0.7Co0.3)2B compound, making this system interesting, for example, in the context of permanent magnet replacement materials or in other areas where a large magnetic anisotropy is of importance.
Despite significant progress in the study of materials undergoing first-order magnetic phase transitions accompanied by the so-called giant magnetocaloric effect (MCE), Gd metal still remains the ...most widely used material in prototypes of magnetic refrigerators due to its significant MCE, good machinability and reasonable mechanical and chemical stabilities. Alloying of Gd enables fine-tuning the Curie temperature of Gd-based solid solutions (all show second-order phase transitions), for graded magnetocaloric materials. Commonly, Gd packed spheres are used as a magnetocaloric working substance in the active magnetic regenerator (AMR) cycle. In this work, we show that the optimized stacking parallel-plate geometry of AMR bed made of Gd is more effective for application at frequencies 1–10 Hz then the packed spheres. We also give a short review on magnetocaloric properties of cold-rolled Gd-X (X = Y, In, Zr, Ga, B) solid solutions. These materials can be produced in the form of thin (∼100 μm) foils/plates to ensure rapid heat exchange between to the heat transfer fluid. Although the magnetocaloric effect decreases in the as-rolled foils, it can be recovered by thermal treatment of the final stacked-plates regenerators. Gd-Y, Gd-In and Gd-Zr solid solutions have magnetocaloric properties, comparable to the MCE of pure Gd in a wide temperature working span up to 37 K, 36 K, and 16 K respectively, which makes them suitable magnetocaloric material systems for testing the fundamental heat exchangers geometries at ambient temperature and in frequencies of 1–10 Hz.
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•We compared 3 principal geometries of Gd heat exchangers: plates, wires and spheres.•Optimal geometry was found to be stacked plates of 100–300 μm with 15–20% porosity.•Gd-X (X = Y, In) solid solutions were used to make stacked plate heat exchangers.•Cold rolling was used to fabricate Gd-X strips with good mechanical properties.•Depression of magnetic properties in as-rolled Gd-X plates has reversible character.
—
Rapidly quenched Mn
55
Al
36
Ga
9
ribbons have been obtained using a spinning method. In the initial quenched state, the ribbon structure is a two-phase one consisting of the ε and γ
2
phases. It ...has been established that, upon heating, the alloy undergoes a series of phase transformations, including the precipitation of the equilibrium β-Mn phase and its subsequent dissolution, the formation of the ferromagnetic τ phase from both the ε and γ
2
phases. The largest amount of the τ phase was obtained by annealing at a temperature of 700°C for 20 min. This work describes both the phase composition obtained as a result of annealing at different temperatures and the features of the microstructure studied via electron microscopy.
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