X-ray diffraction, Mössbauer spectroscopy and magnetization measurements were used as complementary methods to obtain structural data and to determine magnetic properties of the mechanically ...synthesized and subsequently thermally treated Co–Fe–Ni alloys. New, however approximate, phase diagrams were established on the basis of X-ray diffraction investigations. Mössbauer spectroscopy and magnetization measurements allowed to reveal practically linear correlation between the average values of the hyperfine magnetic field induction, 〈
B
hf
〉, and the effective magnetic moments,
μ
eff
, of the alloys. The decrease in 〈
B
hf
〉 with the number of electrons per atom,
e/a, was observed. Moreover, the dependence of
μ
eff
on the valence 3d and 4s electrons per atom follows the Slater–Pauling curve. Thermal treatment of mechanosynthesized Co–Fe–Ni alloys led to some changes in the phase diagrams, increase in the grain size and decrease of the level of internal strains in alloys. Dependencies of lattice constants, average hyperfine magnetic fields, effective magnetic moments and Curie temperatures on the number of electrons per atom have the same trends for mechanically synthesized as well as for thermally treated alloys.
The structure, hyperfine interactions and magnetic properties of the series of multiferroic Bim+1Ti3Fem−3O3m+3 Aurivillius compounds with m=4–8 were studied using X-ray diffraction, 57Fe Mössbauer ...spectroscopy and vibrating sample magnetometry. Samples were prepared by the conventional solid-state sintering method. Bulk magnetic measurements showed that for m=4 the compound is paramagnetic down to 2K while in the compound with m=5 the antiferromagnetic type transition was observed at 11K. In the case of compounds with m=6–8 much more complex magnetic behavior was found. For these compounds a gradual spin freezing and antiferromagnetic spin glass-like ordering were observed on decreasing temperature. The temperature of spin glass freezing was determined as 260, 280 and 350K for m=6, 7 and 8, respectively. Room-temperature Mössbauer spectra of all the compounds studied confirm their paramagnetic state. However, liquid nitrogen and liquid helium temperature measurements reveal magnetic ordering with a residual paramagnetic phase contribution for the compounds with m=5–8.
•Aurivillius compounds prepared by solid-state sintering.•Coexistence of antiferromagnetic and paramagnetic phases seen by Mössbauer spectra.•Hyperfine interactions parameters of compounds determined.•Antiferromagnetic spin glass-like ordering observed down to 10K.
In this work, BiFeO
3
powders were synthesized by a sol–gel method. The influence of annealing temperature on the structure and magnetic properties of the samples has been discussed. X-ray ...diffraction studies showed that the purest phase was formed in the temperature range of 400 °C to 550 °C and the samples annealed at a temperature below 550 °C were of nanocrystalline character. Mössbauer spectroscopy and magnetization measurements were used as complementary methods to investigate the magnetic state of the samples. In particular, the appearance of weak ferromagnetic properties, significant growth of magnetization, and spin-glass-like behavior were observed along with the drop of average grain size. Mössbauer spectra were fitted by the model assuming cycloidal modulation of spins arrangement and properties of the spin cycloid were determined and analyzed. Most importantly, it was proved that the spin cycloid does not disappear even in the case of the samples with a particle size well below the cycloid modulation period
λ
= 62 nm. Furthermore, the cycloid becomes more anharmonic as the grain size decreases. The possible origination of weak ferromagnetism of the nanocrystalline samples has also been discussed.
Ceramic solid solution described by formula Bi0.5Nd0.5FeO3 was prepared by standard solid-state sintering method. X-ray diffraction proved the formation of a single-phase sample with orthorhombic ...structure typical of NdFeO3. Vibrating sample magnetometry revealed weak ferromagnetic behavior of the ceramics up to the Curie temperature Tc = 642 K. Local atomic configurations and local magnetic fields were investigated by 57Fe Mössbauer spectroscopy. It was shown that substitution of a single Nd3+ ion by Bi3+ ion in the orthorhombic NdFeO3 lattice causes a decrease of hyperfine magnetic field experienced by 57Fe ion by the value of 0.186 T. Measurements of the magnetoelectric effect showed that the maximal registered value of the magnetoelectric voltage coefficient was equal to 0.46 mV/(cm·Oe).
•Bi1−xNdxFeO3 ceramic solid solutions were prepared by solid-state sintering.•Structural phase transition from rhombohedral to orthorhombic was observed.•The lattice parameters decrease with an ...increase of Nd concentration.•The value of hyperfine magnetic field monotonically increases with Nd content.•The isomer shift typical for high-spin Fe3+ ions decrease with Nd content.
The series of polycrystalline ceramic powders, Bi1−xNdxFeO3 (x=0.1−1) was successfully synthesized by mixed oxide method followed by pressureless sintering. X-ray diffraction and Mössbauer spectroscopy were used as complementary methods to study structure and hyperfine interactions of the samples. It was found that with an increase of Nd content, within the range of x=0.2−0.3 a structural phase transition from rhombohedral to orthorhombic system occurs. The lattice parameters and unit-cell volume decrease with an increase of Nd concentration. The Mössbauer spectra registered for Bi1−xNdxFeO3 are characterized by sextets with slightly broadened lines and reveal distributions of hyperfine magnetic fields. It was found that the value of the hyperfine magnetic field induction monotonically increases with Nd content. The mean values of isomer shift are typical for Fe3+ ions in a high spin state and slightly decrease from 0.40mms−1 for x=0.3 to 0.37mms−1 for x=0.9. The small value of quadrupole shift confirms octahedral coordination of the iron ions. The structural transition is accompanied by an increase of isomer shift and a change of sign of quadrupole shift.
X-ray diffraction and Moessbauer spectroscopy were applied as complementary methods to investigate the structure and hyperfine interactions in the Bi9Ti3Fe5O27 compound. Samples were synthesized by ...the solid-state sintering method at various temperatures as well as by mechanical alloying. An X-ray diffraction analysis proved that the sintered compounds formed single phases at a temperature above 993K, while the mechanosynthesized material needed additional thermal treatment to complete the single phase formation. Moessbauer studies confirmed the diffraction measurements. Compounds, both those prepared by a solid-state route and fired at 993K and those mechanically alloyed contained residual hematite, however, those sintered at elevated temperatures and mechanically alloyed and subsequently annealed at 1173K were single-phased materials. Room-temperature Moessbauer spectra of the Bi9Ti3Fe5O27 compound revealed their paramagnetic properties suggesting that the Neel temperature of this ceramic was lower than room temperature.
Three different methods were used to obtain Bi
Ti
FeO
ceramics, i.e. solid-state sintering, mechanical activation (MA) with subsequent thermal treatment, and electrical discharge assisted mechanical ...milling (EDAMM). The structure and magnetic properties of produced Bi
Ti
FeO
samples were characterized using X-ray diffraction and Mössbauer spectroscopy. The purest Bi
Ti
FeO
ceramics was obtained by standard solid-state sintering method. Mechanical milling methods are attractive because the Bi
Ti
FeO
compound may be formed at lower temperature or without subsequent thermal treatment. In the case of EDAMM process also the time of processing is significantly shorter in comparison with solid-state sintering method. As revealed by Mössbauer spectroscopy, at room temperature the Bi
Ti
FeO
ceramics produced by various methods is in paramagnetic state.
A series of Co-rich CoxFeyNiz alloys was successfully produced using the mechanical alloying method. To check the stability of their structure thermal treatment was applied subsequently. Mössbauer ...spectroscopy and X-ray diffraction were used to investigate some structural and micro-magnetic properties of mechanosynthesized as well as thermally treated alloys. X-ray diffraction measurements proved that during mechanical alloying solid solutions with b.c.c. or f.c.c. lattices were formed, while thermal processing in some cases provided to decomposition into the mixture of b.c.c. and f.c.c. phases. Mössbauer spectra were fitted using hyperfine magnetic field distribution method. The average value of hyperfine magnetic field induction ranged from 31.5 to 35.5 T. In the case of some thermally treated samples, shapes of distributions reflect two-phase character of the alloys. For this reason curves of distribution were numerically fitted using two Gaussian functions, which were attributed to the suitable phases. The area of individual components was calculated.
Fe–Ni alloys were prepared both by low- and high-energy ball milling processes. Structure and magnetic properties were studied by using X-ray diffraction, differential scanning calorimetry, Mössbauer ...spectroscopy and magnetization measurements. Mechanical treatment influenced the magnetic properties of Fe–Ni alloys as compared with the equilibrium alloys. Reduction of grain size resulted in the increase of magnetization. Invar anomaly for 35 at% Ni was not detected.
Mechanical alloying method was applied to prepare Co
50Fe
40Ni
10, Co
40Fe
40Ni
20, Co
50Fe
35Ni
15 and Co
60Fe
30Ni
10 alloys. X-ray diffraction and Mössbauer spectroscopy were used as complementary ...methods to obtain structural and hyperfine interactions data of the as-milled samples. X-ray diffraction proved that during mechanical alloying process the solid solutions with b.c.c. lattice were obtained in the case of Co
50Fe
40Ni
10, Co
50Fe
35Ni
15 and Co
60Fe
30Ni
10 alloys, while for Co
40Fe
40Ni
20 composition the solid solution with f.c.c. lattice was formed. Result obtained for Co
50Fe
40Ni
10 alloy is consistent with the phase diagram for the Co–Fe–Ni bulk alloys prepared by melting. On the other hand, the milling process of Co
40Fe
40Ni
20, Co
50Fe
35Ni
15 and Co
60Fe
30Ni
10 alloys resulted in the formation of the single solid solution, while for these chemical concentrations the melted alloys are a mixture of b.c.c
+
f.c.c. phases. Mössbauer spectroscopy revealed hyperfine magnetic field distributions, which reflected the different surroundings of
57Fe isotopes by Co, Fe and Ni atoms, depending on the chemical composition of the alloy. The most probable atomic configurations were determined on the basis of the local environment model.
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