Mössbauer studies of hyperfine fields in disordered Fe2CrAl

Heusler-like alloy Fe₂CrAl was prepared and studied. Structure determination was done by X-ray. The structure was found to conform to the B₂ type. Magnetic hyperfine fields in this sample were studied by the Mössbauer effect. The Mössbauer spectra were recorded over a range of temperature from 40 to 296 K. The Mössbauer spectra showed the co-existence of a paramagnetic part with a magnetic hyperfine portion at all recorded temperatures. Even with the distribution in the magnetic hyperfine field, the average hyperfine field follows the (T/T _c)^3/2 law. The paramagnetic part of the hyperfine field is explained in terms of the clustering of Cr atoms.     

Mössbauer study of phase separation in Ni80 57Fe1P19 amorphous alloys

Mössbauer spectroscopy, X-ray diffractometry, scanning calorimetry and electrochemical measurements were used to study the crystallization process of Ni₈₀ ⁵⁷Fe₁P₁₉ amorphous alloys kept in melt at different temperatures before quenching. Samples were heated up to 430°C and 720°C at a rate of 20°C/min, in order to reach characteristically different stages of crystallization. Even at the same crystallization, stage the room temperature Mössbauer spectra and the X-ray differactograms were different depending on the temperature (1050°C or 1400°C) at which the samples were kept before quenching the melt. The Mössbauer spectra showed a paramagnetic component and two sextets (H=267 kOe and H=245 kOe) at 430°C while at 720°C there was only one sextet (H=267 kOe) besides the paramagnetic component. The changes in the Mössbauer spectra of different samples due to crystallization are consistent with the explanation that phase separation occurs in Ni₈₀ ⁵⁷Fe₁P₁₉ rapidly quenched from the melting temperature of 1050°C.     

Mössbauer spectroscopic studies of ruthenium trichlorides

Mössbauer spectra at 5 K and magnetic susceptibilities from 4 K to room temperature have been measured on samples of anhydrous ruthenium trichlorides. The Mössbauer spectrum of α-RuCl₃ shows a magnetic hyperfine splitting in agreement with the result of magnetic susceptibility measurement, while β-RuCl₃ is found to be paramagnetic down to 4 K.     

Magnetic behavior of amorphous Fe−Ni−Zr alloys and their response to radiation damage

The magnetic properties of two amorphous Fe?Ni?Zr alloys, Fe_89.7Ni_0.03Zr₁₀ and Fe₇₀Ni₂₀Zr₁₀, both in the “as cast” and neutron irradiated states were investigated by Mössbauer spectroscopy and dc magnetic susceptibility measurements. The upper magnetic ordering temperatures of Fe_89.7Ni_0.03Zr₁₀ are 232K and 246K for the “as cast” and irradiated samples, respectively. The magnetic ordering temperature for Fe₇₀Ni₂₀Zr₁₀ was about 478K for both the “as cast” and irradiated samples. Both compositions yield magnetic hyperfine spectra, which show a considerable relaxation effect that must be explicitly considered in the calculation of the average local Fe moments. When this is done, these values derived from Mössbauer spectra are in good agreement with the dc susceptibility values. The effects of neutron irradiation on the magnetic properties of these alloys are small.     

Magnetic phase diagram of the FexMn0.7-xAl0.3 alloys series obtained by Mössbauer spectroscopy

By Mössbauer spectroscopy the magnetic phase diagram of the Fe_xMn_0.7-xAl_0.3 spin glass alloy has been obtained. X-ray diffraction (XRD) has shown that all the alloys are in the BCC phase. The broad spectral lines observed in the Mössbauer spectra are indicative of the disordered character of these alloys. Depending on the composition and the temperature the alloys behave as paramagnetic (P), ferromagnetic (F) and reentrant spin glass (RSG). For the alloys rich in iron the only detected magnetic transition is from F to P. For medium iron content two transitions were observed, namely from RSG to F and from F to P. The RSG phase is obtained as a consequence of the disordered character of the alloys and the competitive exchanges due to iron and manganese atoms.     

Local spin configurations of Fe atoms in the Rh1−x Fex (x=0.1, 0.2, and 0.3) system with competing exchange interactions

The local spin configurations of Fe atoms in the magnetically ordered alloys Rh_1?x Fe_x (x=0.1, 0.2, and 0.3) have been investigated by Mössbauer spectroscopy. The Mössbauer absorption spectra are measured in the range from 5 K to temperatures of the transition to the paramagnetic state. The measurements in magnetic fields with a strength up to 5 T are carried out at a temperature of 4.2 K. Analysis of the magnetic-hyperfinefield distribution functions demonstrates that Fe atoms form discrete sets of collinear spin configurations corresponding to different net moments of the nearest coordination sphere. The spin structure of the alloys is governed by a random distribution of Fe atoms over the lattice sites and the competition between the Fe-Rh ferromagnetic exchange interaction and the antiferromagnetic interaction of the neighboring Fe atoms. No spin frustration and spin “melting” effects characteristic of spin glasses are revealed in the Rh-Fe alloys.     

Mössbauer study of SnO<Subscript>2</Subscript> powders doped with dilute <Superscript>57</Superscript>Fe prepared by a sol-gel method

SnO₂ powders, doped with various ⁵⁷Fe contents were prepared by a sol-gel method, and annealed finally at 500 °C and 650 °C. These samples were characterized by Mössbauer spectroscopy, vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) to investigate the relationship of magnetic properties, grain sizes, annealing temperatures and Mössbauer parameters. The particle sizes of SnO₂ powders reduced to less than 100 nm with the increase of Fe contents up to 5%. Rutile SnO₂ was the only phase obtained for all samples. Room temperature Mössbauer spectra suggest the presence of two different paramagnetic iron sites for all samples and one magnetically relaxed species for those samples with the lowest iron concentrations. The magnetization increased with the Fe content, but was reduced for the samples annealed at 650 °C perhaps due to a segregation of α-Fe₂O₃ doped with tin.     

Evidence of magnetic broadening in Mössbauer spectra of superconducting FeTe 0.8 S 0.2

Magnetic properties of the FeTe_0.8S_0.2 superconductor were studied by Mössbauer spectroscopy. Low-velocity Mössbauer spectra that were recorded in the temperature range from 5.7 K up to 300 K show a paramagnetic doublet with a broadening at temperatures below 77 K. The broadening can be explained by the appearance of a distribution of hyperfine magnetic fields due to the magnetic ordering of a part of the sample. The magnetically ordered fraction starts to decrease at temperatures below 20 K indicating a possible competition with the onsetting superconductive state.     

Sol-gel synthesis and dilute magnetism of nano MgO powder doped with Fe

Mg oxides doped with 1 % ⁵⁷Fe were prepared by a sol-gel method, and annealed at various temperatures. Nano-size Mg oxides were characterized by Mössbauer spectrometry, magnetization and XRD measurements. The crystalline size of MgO increases with increase of annealing temperature. Samples annealed at 600 °C and 800 °C gave only doublet peaks of paramagnetic Fe³⁺ in Mössbauer spectra although Fe³⁺ doping into MgO induced a distorted structure and showed weak ferromagnetism. It is considered that the magnetic property is due to defect induced magnetism by doping Fe³⁺ into MgO. For a sample heated at 1000 °C, it is found from low temperature Mössbauer spectra that Fe³⁺ species are located at the core and shell of fine MgFe₂O₄ grains and diluted in MgO matrix.     

Mössbauer and X-ray study of the Fe 65 Ni 35 invar alloy obtained by mechanical alloying

Fe₆₅Ni₃₅ samples were prepared by mechanical alloying (MA) with milling times of 5, 6, 7, 10 and 11 h, using a ball mass to powder mass ratio of 20:1 and at 280 rpm. The samples were characterized by X-ray diffraction (XRD) and transmission ⁵⁷Fe Mössbauer spectrometry. The X-ray diffraction pattern showed the coexistence of one body centered cubic (BCC) and two face centered cubic (FCC1 and FCC2) structural phases. The lattice parameters of these phases did not change significantly with the milling time (2.866 Å, 3.597 Å and 3.538 Å, respectively). After 10 h of milling, the X-ray diffraction pattern showed clearly the coexistence of these three phases. Hence, Mössbauer spectrometry measurements at low temperatures from 20 to 300 K of this sample were also carried out. The Mössbauer spectra were fitted using a model with three components: the first one is a hyperfine magnetic field distributions at high fields, related to the BCC phase; the second one is a hyperfine magnetic field distribution involving low hyperfine fields related to a FCC phase rich in Ni, and the third one is a singlet related to a FCC phase rich in Fe, with paramagnetic behavior. As proposed by some authors, the last phase is related with the antitaenite phase.     

Some magnetic properties of the cores of various ferritins

⁵⁷Fe Mössbauer spectra of the mineral cores of various ferritins show both paramagnetic and superparamagnetic relaxation effects and in some cases a combination of both. Correlations have been observed between data on the crystallinity, phosphate content and percentage iron in the cores and their magnetic ordering and mean blocking temperatures derived from the Mössbauer spectra.     

Mössbauer studies of the re-entrant spin-glass behaviour of Fe–Al alloys

Fe–Al alloys around the concentration of 30 at. % Al present re-entrant spin-glass behaviour at low temperatures. This behaviour is not completely understood and Mössbauer spectroscopy, combined with other experimental techniques, is useful to describe and explain this behaviour. Results show that the Mössbauer spectra coincide with the magnetic behaviour showed in literature and they can be explained as a magnetic cluster system whose magnetic clusters are getting smaller when the temperature is decreasing. When the temperature is reaching to the spin-glass transition at 92 K the spins in the paramagnetic matrix are moving slower and below this transition the spins are completely frozen.     

Magnetic insulator glasses

An outline is given of the use of Mössbauer spectroscopy as a probe of the amorphous structure and magnetic coordination in magnetic insulator glasses. Using the⁵⁷Fe Mössbauer resonance as an example in the context of amorphous ferric oxides and fluorides, the manner in which both paramagnetic and hyperfine-field-split spectra can be analyzed is presented. Emphasis is given to the information contained in Mössbauer lineshapes and linewidths in addition to the more obvious line-position data. A number of general findings are set out for ferric speromagnetics with particular references to Mössbauer studies of amorphous Fe₂O₃, Y₃Fe₅O₁₂ (YIG), FeF₃ and NaFeF₄.     

Mössbauer spectroscopy of zirconium alloys

Mössbauer investigations of zirconium alloys were examined. Data about the chemical state of iron atoms in the zirconium alloys of different composition has been provided. Mössbauer spectroscopy revealed that small quantities of iron in binary zirconium alloy are in the solid solution α-Zr (up to 0.02 wt.%). Different iron atoms concentration and thermo-mechanical treatments may lead to formation the intermetallic compounds Zr₃Fe, Zr₂Fe, ZrFe₂. Adding tin atoms does not affect the formation and shape of Mössbauer spectra of these compounds. Adding Cr and Nb atoms makes significant changes in the shape of Mössbauer spectra and leads to the formation of complex intermetallic compounds. Adding Cu and W atoms, the shape of the binary alloys spectra (Zr-Fe) remains unchanged, but a change in the temperature dependence behavior of the spectral parameters occurs and also, changes to the properties of the alloys.     

Magnetic and structural properties of mechanically alloyed Tb0.257−x Nd x Fe0.743 alloys, with x = 0 and 0.257

The alloys between a transition metal and a rare earth present magnetic and magneto optical properties of exceptional interest for the production of magnetic devices for information storage. In this work we report the magnetic and structural properties, obtained by Mössbauer spectrometry (MS) and X-ray diffraction (XRD), of Tb_0.257?x Nd _x Fe_0.743 alloys with x?=?0 and 0.257 prepared by mechanical alloying during 12, 24 and 48 h, to study the influence of the milling time in their magnetic and structural properties. The X-rays results show for all the samples that the α-Fe and an amorphous phase are always present. The first decreases and the second increases with the increase of the milling time. Mössbauer results show that the amorphous phase in samples with Nd is ferromagnetic and appears as a hyperfine field distribution and a broad doublet, and that as the milling time increases the paramagnetic contribution increases. For samples with Tb the amorphous phase is paramagnetic and appears as a broad doublet which increases with the milling time and for 48 h milling it appears an additional broad singlet.     

Mössbauer Investigation of Fe–Mn–Cu Nanostructured Alloys Obtained by Ball Milling

Fe₇₉Mn₂₁, (Fe₇₉Mn₂₁)₉₀Cu₁₀, and (Fe₇₉Mn₂₁)₈₀Cu₂₀, alloys, prepared by high energy ball milling were characterized by Mössbauer spectroscopy, X-ray diffraction and ac-susceptibility. Results indicate that the Cu addition favors the formation of a FCC phase with two different magnetic states at room temperature, i.e., an antiferromagnetic and a paramagnetic one. Thermal evolution of the Mössbauer spectra revealed the occurrence of a magnetic ordering along a wide temperature range. This behavior is probably related to Fe atoms in FCC-Fe(Mn,Cu) phase having different environments and grain size distribution. Thermal dependence of in-phase ac-susceptibility shows that a long range ordering starts at 240 K for the Fe₇₉Mn₂₁ alloy and shifts towards lower temperatures with the Cu content. These results would reflect a long-range magnetic ordering transition with a distribution of ordering temperatures rather than a blocking process of particle single-domains.     

Mössbauer study of magnetic anisotropy in electrochemically deposited Fe−Ni−P amorphous alloys

In a previous work [1], a large magnetic anisotropy was found as a preliminary result of the formation of electrochemically deposited Fe₉₃P₇ alloy. Mössbauer spectroscopy was used in order to get information about the magnetic anisotropy of electrochemically prepared Fe?P and Fe?Ni?P amorphous alloys. The Mössbauer spectra and the hyperfine field distributions of the samples show that Fe?Ni?P and Fe?P electrodeposited amorphous materials can be prepared in a reproducible way from a point of view of short range ordering which is strongly dependent on the chemical composition determined by preparation conditions. The average magnetization directions in the samples were determined from the transmission spectra measured in a normal and two tilted geometries by two types of evaluation methods [2,3]. We have found that the small spread model of the domain structure better describes the experimental results. The obtained data reflect the prevailing anomalous magnetization orientation in these electrodeposited amorphous alloys.     

Mössbauer study of high concentration Fe−Ag alloys produced by vapour quenching

Mössbauer spectra have been observed for Fe?Ag alloys sputter-deposited on liquid nitrogen cooled substrates and water cooled substrates under several Ar gas pressures, P_Ar. The magnetic hyperfine field does not depend on the substrate temperature. However, in paramagnetic spectra, a single line component corresponding to isolated Fe atoms in the Ag matrix is more pronounced for the alloys deposited on liquid nitrogen cooled substrates. The alloys deposited under high P_Ar reveal very weak intensity ratios of the second and fifth lines of the ferromagnetic sextet, indicating a tendency of perpendicular magnetic anisotropy.     

Mössbauer study of Fe70Cr10C10P10 rapidly quenched alloys

Mössbauer spectroscopy was used to study rapidly quenched Fe₇₀Cr₁₀C₁₀P₁₀ amorphous alloys in order to get information about the effect of some preparation parameters on the structure and properties of the alloys. The results indicate that the Mössbauer spectroscopy can sensitively detect changes with quenching rate in these amorphous alloys. The average magnetic field decreases with increasing thickness of the samples. This cooling rate effect was compared with low temperature relaxation changes of the aged thin samples.