Hyperfine Magnetic Field Values Research Articles

Spin-reorientation in the antiferromagnetic ordering of LiFe1-xMnxPO4 investigated with Mössbauer spectroscopy

The crystal structures of LiFe1-xMnxPO4 (x = 0.1, 0.3, 0.5) samples have been characterized with x-ray diffraction (XRD) and were determined to be orthorhombic with space group Pnma by Rietveld refinement method. The temperature dependence of the magnetization curves showed abnormal antiferromagnetic behavior as well as a decrease in Neel temperature (TN) with Mn substitution from superconducting quantum interference device (SQUID) measurement. The magnetization decreases until the temperature reaches the spin-reorientation temperature (TS), and then increases with temperature up to TN. The Mossbauer spectra of the LiFe1-xMnxPO4 show that the magnetic hyperfine field (Hhf) and electric quadrupole splitting (ΔEQ) values change with increasing temperature, compared to values at TS, which is caused by the strong electric crystalline field originating from distorted octahedral symmetry. The decrease in TS of LiFe1-xMnxPO4 can be explained by the Mn-concentration-dependent crystal field and spin-orbit coupling...

Structural properties and hyperfine characterization of Sn-substituted goethites

Tin-doped goethites obtained by a simple method at ambient pressure and 70°C were characterized by inductively coupled plasma atomic emission spectrometry, scanning electron microscopy, Rietveld refinement of powder X-ray diffraction data, and 57Fe and 119Sn Mössbauer spectroscopy.The particles size and the length to width ratios decreased with tin-doping. Sn partially substituted the Fe(III) ions provoking unit cell expansion and increasing the crystallinity of the particles with enlarged domains that grow in the perpendicular and parallel directions to the anisotropic broadening (111) axis. Intermetallic E, E′ and DC distances also change although the variations are not monotonous, indicating different variations in the coordination polyhedron. In general, the Sn-substituted samples present larger intermetallic distances than pure goethite, and the greatest change is shown in the E′ distance which coincides with the c-parameter.119Sn Mössbauer spectroscopy revealed that Sn(II) is incorporated as Sn(IV) in the samples. On the other hand, Fe(II) presence was not detected by 57Fe Mössbauer spectroscopy, suggesting the existence of vacancies in the Sn-doped samples. A lower magnetic coupling is also evidenced from the average magnetic hyperfine field values obtained as tin concentration increased.

Structural, magnetic and thermal properties of intermetallics Nd 3Fe 27− xCo xV 2 ( x = 0, 2 and 4) and their hydrides

Intermetallics of the Nd 3Fe 27− x Co x V 2 ( x = 0, 2 and 4) system with monoclinic type structure and their hydrides were prepared by arc melting and exposed to hydrogenation. The effects of Co substitution of Fe on the magnetic hyperfine fields of intermetallic compound Nd 3Fe 27V 2, as well as the effects of interstitial hydrogen additions on the symmetry and local magnetic properties in these systems were studied. The investigations were performed by powder X-ray diffraction, Mössbauer spectroscopy and simultaneous TGA-DSC. Both site populations and magnetic hyperfine field strength were analyzed in order to discriminate between the Co and H contributions to the local atomic environments in these systems. The values of magnetic hyperfine fields corresponding to inequivalent lattice sites were found to be enhanced after the increase in Co content and hydrogenation. Slight changes in the relative site occupancies were observed. Simultaneous TGA-DSC studies showed that the amount of hydrogen insertion decreased slightly with the increase of Co contents, while the enthalpy associated with hydrogen desorption decreased sharply under heat treatment. The Nd 3Fe 27− x Co x V 2 ( x = 0, 2 and 4) and their hydrides are not stable under treatment and two exothermic peaks are observed in the DSC curves, corresponding to the decomposition of the monoclinic phase with the precipitation of α-Fe phase.

Magnetic and interface properties ofFe0.82Ni0.18/Co(001) superlattices

The thickness dependence of the Fe magnetic hyperfine field and the interfacial intermixing ofFe0.82Ni0.18/Co superlattices, with the same thickness for FeNi and Co layers, have been investigated. Alocal concentration model using the magnetic hyperfine field values from the[Fe0.82Ni0.18]1 − xCox alloys has been used to interpret the field distribution in the superlattices and the Coconcentration profiles over the superlattices. A relationship between the Fe magnetichyperfine field and the Fe magnetic moment has been determined for the unordered[Fe0.82Ni0.18]1 − xCox andFe1 − xCox alloys. The magnetic hyperfine fields have been explained using two Fermi contact terms: (i) thecore electron term proportional to the Fe magnetic moment with a proportionality constant of − 13 T/μB and(ii) a valence electron term linearly dependent on the Co concentration. The direction of the magneticmoments is found to be in the sample plane except for the 1/1 superlattice, where an angle of about45° is found.

Composition-dependent magnetic properties ofBiFeO3-BaTiO3solid solution nanostructures

We report on the M\ossbauer spectra and magnetization properties of single-crystalline ${({\text{BiFeO}}_{3})}_{x}\text{\ensuremath{-}}{({\text{BaTiO}}_{3})}_{1\ensuremath{-}x}$ solid solution nanostructures in the form of nanocubes, measuring approximately 150 to 200 nm on a side, prepared by a molten salt solid-state reaction method in the compositional range wherein $0.5\ensuremath{\le}x\ensuremath{\le}1$. Powder x-ray diffraction (XRD) and monochromatic synchrotron XRD studies indicate products of high purity, which undergo gradual, well-controlled structural transformations from rhombohedral to tetragonal structures with decreasing ``$x$.'' For all solid solution products, room-temperature magnetization studies exhibit hysteretic behavior with remnant magnetization values of ${M}_{\text{r}}\ensuremath{\ge}0.32\text{ }\text{emu}/\text{g}$, indicating that the latent magnetization locked within the toroidal spin structure of ${\text{BiFeO}}_{3}$ has been released. Room-temperature M\ossbauer spectra show composition-dependent characteristics with decreasing magnetic hyperfine field values and increasing absorption linewidths due to a decrease in the magnetic exchange interaction strength with decreasing $x$. For the lowest $x=0.5$ composition studied, the M\ossbauer spectra show paramagnetic behavior, indicating a N\'eel temperature for this composition below 300 K. However, room-temperature magnetization studies with applied fields of up to 50 kOe show hysteretic behavior for all compositions, including the $x=0.5$ composition, presumably due to field-induced ordering. Furthermore, hysteresis loops for all compositions exhibit smaller coercivities at 10 K than at 300 K, an observation that may suggest the presence of magnetoelectric coupling in these systems.

57Fe Mossbauer spectroscopy and electrical resistivity studies on naturally occurring native iron under high pressures up to 9.1 GPa

We report the pressure dependence of the Mössbauer spectra and the electrical resistivity up to 9.1 GPa at room temperature for a native iron sample collected from the Precambrian Chaibasa shales, Singhbhum Craton, Eastern India. The Mössbauer spectroscopy of the sample at ambient conditions yields isomer shifts and magnetic hyperfine field values that confirm the presence of Fe0 oxidation state. Many theories have been put forward to explain the origin of this native iron including a Precambrian meteoritic impact. High-pressure Mössbauer spectroscopic measurements using diamond anvil cell (DAC) showed a constant isomer shift up to 5.6 GPa with a subtle variation of -1.07 × 10-3 mm/s/GPa followed by sharper change -4.3 × 10-3 mm/s/GPa above 6.3 GPa, a pressure much lower than the usual value reported for metallic iron. Further increase of pressure to 9.1 GPa results in the emergence of a tiny peak at ~0 isomer shift indicating the onset of the martensitic phase transition of iron from the body-centered-cubic (bcc) to hexagonal-close-packed (hcp) transition 4 GPa lower than the transition pressure normally observed for pure iron. This phase transition in the native iron is confirmed by high-pressure electrical resistivity study. Lowering of the transition pressure could be due to nucleation of hcp by stacking faults caused by shock metamorphism resulting from the Precambrian impact in the region.

IMSG09: A 57Fe-119Sn Mössbauer spectra computer fitting program with novel interactive user interface

A recently developed computer based 57Fe-119Sn Mössbauer spectra fitting program is described. The program uses full Hamiltonian matrices to generate theoretical Mössbauer spectral contributions with which fits the experimental data based on a least-squares minimization procedure. The user of the program can exploit its interactive user interface to built and modify on-the-fly a starting theoretical model of proposed contributions without the need to write or alter the initial Mössbauer parameter values to or from any file. Changes in the Mössbauer parameters values for the proposed model can be made on the screen and the theoretical contributions can be displayed during those changes in real time together with the experimental spectrum in order to give the user the ability to approximate with the best and fast way the desired solution before launching the minimization procedure. Single as well as multiple sub-component contributions with Gaussian-type spreading of quadrupole splitting/shift or hyperfine magnetic field values can be realized to fit transmission, conversion electron or X-ray Mössbauer spectra of randomly or non-randomly oriented powder or single crystal samples. The program is currently written for 3/2→1/2 nuclear spin transitions but can be modified to include higher spins, as well as distributions of other types and of other Mössbauer parameters values.

Influence of Mn-for-Fe substitution on structural properties of synthetic goethite

In order to study the effect of alloying elements, such as manganese, on the properties of the rust on weathering steels, a series of Mn-goethite samples containing different amounts of Mn were synthesized from ferrihydrite in alkaline media. The samples were characterized by X-ray diffraction (XRD) and Mossbauer spectroscopy. The cell parameters calculated from the XRD patterns showed clearly that the a- and c-parameters decrease while the b-parameter increases with increasing Mn concentration, indicating that the octahedra of the goethite structure become distorted by an incorporation of Mn (Jahn–Teller-effect). Mossbauer spectra of the samples were recorded at room temperature (RT) and at 80 K. The quadrupole shift values gradually decrease with increasing Mn substitution in the goethite structure. It has been observed that the magnetic hyperfine field values of maximum probability are reduced with increasing Mn in the samples. No doublet component was observed in the RT MS spectra suggesting that no effects of superparamagnetim resulting from smaller particles are present.

Magnetic properties of neutron irradiated RPV steel

The neutron irradiated reactor pressure vessel (RPV) steels at various dose of 0–1018 n/cm2 have been studied with Mossbauer, x-ray diffraction, and VSM. The Mossbauer data shows that the value of magnetic hyperfine field of Fe atom that exist at martensite is 330 kOe at site 1 and 305 kOe at site 2. At room temperature, the total absorption area of Mossbauer spectra with respect to irradiation of neutron is constant for the dose of 0–1016 n/cm2, while over the dose of 0–1017 n/cm2 the absorption area decreases rapidly. But the doublet area for the dose of 0–1016 n/cm2 is constant, while over the dose of 1017 n/cm2 it increases with increasing the fluence level of neutron. The coercivity and remanence of the neutron irradiated samples do not change significantly. But the maximum induction decreases by 5% at 1018 n/cm2, compared with that of the as-received sample.

Structural and magnetic characterization of Fe/Cr/Fe tri‐layers and Fe/Cr multilayers after swift Au ion irradiation

AbstractFe/Cr/Fe trilayers and Fe/Cr multilayers were irradiated by 163 MeV Au ions with fluence of 1 × 1011 ions/cm2 to 50 × 1011 ions/cm2. The structural properties of Fe/Cr interfaces were observed using Conversion Electron Mössbauer Spectroscopy (CEMS) and X‐ray reflectivity (XRR). The magnetic exchange coupling between Fe layers through Cr spacer in trilayers and multilayers was determined from hysteresis loops measured with SQUID magnetometer. The different behavior of Fe/Cr/Fe trilayers and Fe/Cr multilayers was observed after Au ions irradiation. In Fe/Cr multilayers a decrease of the average value of hyperfine magnetic field with increasing Au ions fluence was observed, indicating an increase of the inter‐ increase of the interfacial roughness. In Fe/Cr/Fe trilayers the non‐monotonic behavior of average value of hyperfine magnetic field versus ion fluence was observed suggesting the smoothing of the interfaces at small fluences and roughening at higher ones. The smoothening of interfaces was confirmed by XRR spectra. In multilayers the magnetic properties changed in a similar way as the structural properties and continuous decay of antiferromagnetic coupling as a function of fluence was observed. In trilayers at the low fluences the antiferromagnetic coupling was not sensitive on irradiation, while at large fluences the decrease of antiferromagnetic coupling fraction was seen. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of the milling conditions on the formation of nanostructured Fe–Co powders

AbstractNanostructured Fe–12Co (wt%) powders were prepared by mechanical alloying in a planetary ball mill. The milling process was carried out at different milling conditions. The obtained powders were characterized by X‐ray diffraction, 57Fe Mössbauer spectrometry and magnetic measurements. The low and high speed ball‐milling conditions lead to the formation of a single and two‐bcc Fe(Co) structure, respectively, having different crystallite sizes, microstrains hyperfine parameters and magnetic properties. The average hyperfine magnetic field values: 〈B〉1 = 34.8 T and 〈B〉2 = 28.2 T of the two‐bcc Fe(Co) structure could be attributed to the nanocrystalline grains and to the grain boundaries, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Co0.9Zn0.1Cr1.9857Fe0.02O4물질의 초미세자기장 연구

[ <TEX>$AB_2X_4$</TEX> ]((A, B)=Transition Metal, X=O, S, Se) 물질에서의 8면체 자리의 이온 거동과 4면체 자리 이온과의 상호작용에 대하여 많은 연구가 이루어지고 있다. 본 연구에서는 4면체 자리에 비자성 이온인 Zn 이온을 치환함에 따른 자기구조의 변화를 관측하여 8면체 자리의 자기구조를 분석하고자 하였다. Cr이온의 일부를 Fe로 치환한 <TEX>$[Co_{0.9}Zn_{0.1}]_A[Cr_{1.98}{^{57}Fe_{0.02}}]_BO_4$</TEX>의 닐온도(<TEX>$T_N$</TEX>는 90K로 <TEX>$CoCr_{1.98}{^{57}Fe_{0.02}}O_4$</TEX> 비하여 감소하였다. 4.2 K에서의 초미세자기장값의 분석결과, 초미세자기장값의 작은 차이를 보이는 잘 분리된 2-set 형태로 나타났으며, <TEX>$CoCr_{1.98}{^{57}Fe_{0.02}}O_4$</TEX>의 초미세자기장값은 488, 478 kOe 인데 반하여, <TEX>$Co_{0.9}Zn_{0.1}Cr_{1.98}{^{57}Fe_{0.02}}O_4$</TEX>의 초미세자기장값은 <TEX>$B_1=486$</TEX>, <TEX>$B_2=468$</TEX> kOe으로 나타났다. Zn 이온의 치환에 따라서 초미세자기장값의 변화를 알 수 있었다. 이러한 결과로 인하여, Zn 이온이 x=0.1 치환된 물질의 경우, 스핀재정렬온도(<TEX>$T_S$</TEX>)가 18K으로 감소함을 알 수 있다. [ <TEX>$AB_2X_4$</TEX> ](A, B=Transition Metal, X=O, S, Se) are cubic spinel normal ferrimagnets, in which M ions occupy the tetrahedral sites and Cr ions occupy the octahedral sites. Recently, they have been investigated for behaviour of B site ions and A-B interaction. Polycrystalline <TEX>$[Co_{0.9}Zn_{0.1}]_A[Cr_{1.98}{^{57}Fe_{0.02}}]_BO_4$</TEX> compound was prepared by wet-chemical process. The ferrimagnetic transition was observed around 90K. <TEX>$M\"{o}ssbauer$</TEX> absorption spectra at 4.2K show that the well-developed two sextets are superposed with small difference in hyperfine fields(<TEX>$H_{hf}$</TEX>). The hyperfine fields of <TEX>$CoCr_{1.98}{^{57}Fe_{0.02}}O_4$</TEX> and <TEX>$Co_{0.9}Zn_{0.1}Cr_{1.98}{^{57}Fe_{0.02}}O_4$</TEX> were determined to be 488, 478 kOe and 486, 468 kOe, respectively. We notice that the one of the magnetic hyperfine field values changes with Zn ion substitution. These results suggest the incommensurate states and spin-reorientation temperature(<TEX>$T_S=18K$</TEX>) changes with Zn ions substitution below spin-reorientation temperature(<TEX>$T_S=28K$</TEX>) of <TEX>$CoCr_{1.98}{^{57}Fe_{0.02}}O_4$</TEX>

Hyperfine interactions and local environment ofFe57probe atoms in perovskiteCaMn7O12

M\ossbauer spectroscopy has been applied for studying the local environment of $^{57}\mathrm{Fe}$ probe atoms within iron-doped $\mathrm{Ca}{\mathrm{Mn}}_{7}{\mathrm{O}}_{12}$ manganite with a perovskite-like structure. The $^{57}\mathrm{Fe}$ spectra recorded in the paramagnetic temperature range $90\phantom{\rule{0.3em}{0ex}}\mathrm{K}lTl380\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, where $\mathrm{Ca}{\mathrm{Mn}}_{7}{\mathrm{O}}_{12}$ has a rhombohedral structure $(R\overline{3})$, were discussed supposing ${\mathrm{Fe}}^{3+}$ probe cations to replace manganese in the octahedral $({\mathrm{Mn}}^{3+}{\mathrm{O}}_{6})$ and $({\mathrm{Mn}}^{4+}{\mathrm{O}}_{6})$ polyhedra. A very small $(l3%)$ part of ${\mathrm{Fe}}^{3+}$ probe cations characterized by very large quadrupole splitting $(\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\mathrm{mm}∕\mathrm{s})$ suggests that a few amounts of $^{57}\mathrm{Fe}$ probe can be substituted for ${\mathrm{Mn}}^{3+}$ in the $(9e)$ positions with approximately a square planar surrounding. In the temperature range $380\phantom{\rule{0.3em}{0ex}}\mathrm{K}lTl450\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the $^{57}\mathrm{Fe}$ M\ossbauer spectra undergo a sharp change which can be due to a formation (at ${T}_{\mathrm{C}\mathrm{O}}\ensuremath{\sim}380\phantom{\rule{0.3em}{0ex}}\mathrm{K}$) and a gradual growth with temperature of the cubic manganite phase $(\mathrm{Im}\overline{3})$. At $T\ensuremath{\ge}450\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the $^{57}\mathrm{Fe}$ spectrum reveals single ${\mathrm{Fe}}^{3+}$ sites in an oxygen symmetric octahedral surrounding. This can be well explained by a fast electron exchange ${\mathrm{Mn}}^{3+}\ensuremath{\leftrightarrow}{\mathrm{Mn}}^{4+}$, leading to the crystallographic equivalence of all $\mathrm{Mn}{\mathrm{O}}_{6}$ positions. At the temperature range $Tl{T}_{\mathrm{M}2}$ $(=90\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, an appearance of the distributions of the hyperfine magnetic field values at the $^{57}\mathrm{Fe}$ nucleus up to $\ensuremath{\sim}350\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ (at $77.4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$) was observed. This result is an independent experimental evidence of magnetic ordering in the manganese sublattice.

Hyperfine interactions in (CuFe2O4)1 − x (SnO2) x (x = 0, 1, 5, 10 and 20 wt.%) nanocomposites studied by Mössbauer spectroscopy

A series of (CuFe2O4)1−x (SnO2) x nanocomposites (x=0, 1, 5, 10,20 wt.%) have been prepared by urea-nitrate combustion method. The room temperature Mossbauer spectra of CuFe2O4 and (CuFe2O4)0.99(SnO2)0.01 contained two sextets while remaining samples contained at least four sextets with additional doublet indicating the presence of paramagnetic phase. The variations of isomer shift, quadruple splitting and magnetic hyperfine field values were found with the addition of SnO2.

Charge‐ordering in La0.333Ca0.667MnO3

AbstractWithin the framework of strong electron‐lattice interaction of Mn3+ ions and orbital dependent exchange interaction model, the crystal and magnetic structures of charge ordered phase La1/3Ca2/3MnO3 are studied. The calculation results are in agreement with the “Wigner crystal” model. The estimated superexchange parameters confirm the qualitative conclusions of experimental works about frustrated magnetic structure with magnetic supercell (3a × b × 2c). The values of hyperfine magnetic fields on 55Mn nuclei in different charge states in charge ordering phase are calculated. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Hyperfine interactions in lutetium iron garnet

Nuclear Magnetic Resonance/Near Quadupole Resonace specra of Lu175 in lutetium iron garnet (LuIG) were measured in the range of 10–500MHz in zero external magnetic field at a temperature of 4.2K. Experimentally observed spectra had complicated structure and a theory was needed to interpret them. To this end we calculated the electronic structure of LuIG and from it the values of magnetic hyperfine fields and the components of electric-field-gradient tensor at the lutetium nuclei were determined. These parameters were used to simulate the theoretical spectra of Lu175 in LuIG. Simulated spectral lines of Lu175 at dodecahedral sublattice correspond reasonably well with the system of measured lines in the range of 10–200MHz. Several spectral lines in the range of 300–500MHz can be interpreted as the resonance of Lu175 at the octahedral sites that are nominally occupied by the ferric cations.

Mössbauer investigation of Fe 1−x Cr x films grown by ion-beam sputter deposition

Fe 1− x Cr x ( 0 < x < 0.70 ) films, 220 nm thick, on Si and fused-SiO 2 substrates were prepared using ion-beam sputter deposition, and their structural properties were determined by 57Fe conversion electron Mössbauer spectroscopy (CEMS) and X-ray diffraction experiments (XRD) at room temperature. CEM spectra show magnetic ordering for 0< x⩽0.28, and the BCC α-phase is evidenced through XRD diagrams in all cases. The general trend for the films is that the average hyperfine magnetic field (HMF) values are lower compared to bulk counterparts. Moreover, a parabolic change in average HMF with Cr content x could be established. For 0.32⩽ x<0.70, the CEM spectra exhibit a pseudo-single line, which denotes paramagnetic state. Between x = 0.32 and x = 0.38 , there exists a multiphase region where the alloys mainly consist of α and δ (A15-type) phases. Then, in the concentration range x=0.38–0.58, the films only display the metastable δ-phase. For 0.58⩽ x⩽0.66, there appears a new transition region where α- and δ-phases coexist. Finally, the domain of the paramagnetic α-phase alone stretches from x = 0.66 to at least x = 0.70 . Emphasis is placed on the metastable δ-phase which appears over a wide monophase region. Particularly, the site occupancy could be determined through the CEM spectrum for x = 0.49 .

Hyperfine interactions, structure and magnetic properties of nanocrystalline Co–Fe–Ni alloys prepared by mechanical alloying

Mechanical alloying method was used to prepare nanocrystalline Co50Fe40Ni10, Co52Fe26Ni22 and Co65Fe23Nil2 alloys. X-ray diffraction proved that during milling Co-Fe-based solid solution with b.c.c. lattice was formed in the case of Co50Fe40Ni10, while for Co52Fe26Ni22 and Co65Fe23Nil2 compositions Co-Ni-based solid solutions with f.c.c. lattice were obtained. Mossbauer spectroscopy revealed similar values of the average hyperfine magnetic fields for all alloys, e.g. 32.17, 32.24 and 31.21 T for Co50Fe40Ni10, Co52Fe26Ni22 and Co65Fe23Nil2 alloys, respectively. Magnetization measurements allowed to determine the effective magnetic moment, Curie temperature, saturation magnetization and coercive field for the obtained alloys.

Mössbauer and magnetic studies of MFe2O4(M = Co, Ni) nanoparticles

Nanocrystalline MFe2O4 (M=Co, Ni) particles are synthesized by citrate precursor technique. Mossbauer and magnetic studies are carried out with the CoFe2O4 samples having particle sizes of 9, 14 and 30 nm and the NiFe2O4 samples having particle sizes of 9, 21 and 30 nm. The intrinsic magnetic parameters are found to vary with the particle size. The magnetic interactions and cation distribution present in these systems influence the room temperature Mossbauer parameters. Ferrimagnetic sextets are observed for all the different particle sizes. The observed reduction of the magnetic hyperfine field values with the decrease in the size of MFe2O4 particles are attributed to the intrinsic size effect and the canted spin structure at the surface of the nanoparticles.

Vickers Microhardness and Hyperfine Magnetic Field Variations of Heat Treated Amorphous Fe78Si9B13 Alloy Ribbons

Amorphous Fe78Si9B13 alloy ribbons were heat treated between 296 and 763 K, using heating rates between 1 and 4.5 K/min. Whereas one ribbon partially crystallized at T x = 722 K, the other one partially crystallized at T x = 763 K. The partially crystallized ribbon at 722 K, heat treated using a triangular form for the heating and cooling rates, was substantially less fragile than the partially crystallized at 763 K where a tooth saw form for the heating and cooling rates was used. Vickers microhardness and hyperfine magnetic field values behaved almost concomitantly between 296 and 673 K. The Mossbauer spectral line widths of the heat-treated ribbons decreased continuously from 296 to 500 K, suggesting stress relief in this temperature range where the Vickers microhardness did not increase. At 523 K the line width decreased further but the microhardness increased substantially. After 523 K the line width behave in an oscillating form as well as the microhardness, indicating other structural changes in addition to the stress relief. Finally, positron lifetime data showed that both inner part and surface of Fe78Si9B13 alloy ribbons were affected distinctly. Variations on the surface may be the cause of some of the high Vickers microhardness values measured in the amorphous state.