Average Hyperfine Magnetic Field Research Articles

Mössbauer effect on mechanically alloyed FeN

Mossbauer measurements were carried out on mechanically alloyed 10Fe + 2Fe3N compounds. Hyperfine fields of various local environments for compounds ground in Ar and N2 atmospheres are presented. The initial increase of the average hyperfine magnetic field is reported. Gaseous nitrogen accelerates the process of mechanical alloying. There is no indication of Fe16N2 formation.

Ferromagnetism in the icosahedral Al 62.5B 7.5Pd 15Fe 15 quasicrystal

We have found a new magnetic icosahedral quasicrystal, Al 62.5B 7.5Pd 15Fe 15, in which iron has a magnetic moment. The quasicrystal exhibits ferromagnetic properties. Its Curie temperature is about 305 K and its coercive forces at 5 and 300 K are determined to be 1.2 kOe and 40 Oe, respectively. Mössbauer measurements reveal that only about 12% of the Fe atoms have a magnetic moment, and at 4.2 K the average hyperfine magnetic field at the Fe nuclei is 〈 H hf〉 = 95.5 kOe. The values of the magnetic moments per Fe atom estimated from the 〈 H hf〉 value and from the magnetization value are μ Fe=0.67 β B and 1.63 μ B, respectively. This discrepancy may be attributed to the participation of Pd atoms in the magnetic properties of this i-QC. The formation of bonding between Fe and B is thought to be mainly responsible for the creation of the local moment at Fe.

Ferromagnetism in the icosahedral Al 62.5B 7.5Pd 15Fe 15 quasicrystal

We have found a new magnetic icosahedral quasicrystal, Al 62.5B 7.5Pd 15Fe 15, in which iron has a magnetic moment. The quasicrystal exhibits ferromagnetic properties. Its Curie temperature is about 305 K and its coercive forces at 5 and 300 K are determined to be 1.2 kOe and 40 Oe, respectively. Mössbauer measurements reveal that only about 12% of the Fe atoms have a magnetic moment, and at 4.2 K the average hyperfine magnetic field at the Fe nuclei is 〈 H hf〉=95.5 kOe. The values of the magnetic moments per Fe atom estimated from the 〈 H hf 〉 value and from the magnetization value are μ Fe=0.67 μ B and 1.63μ B, respectively. This discrepancy may be attributed to the participation of Pd atoms in the magnetic properties of this i-QC. The formation of bonding between Fe and B is thought to be mainly responsible for the creation of the local moment at Fe.

Mössbauer effect study of the pseudo-binary system (Ti1−x Nb x )Fe2

Mossbauer spectroscopy and X-ray diffraction measurements have been done on (Ti1−x Nb x )Fe2 compounds in order to investigate the effect of Nb on the magnetic properties of TiFe2. The experimental results show that Nb enters the lattice by filling Ti sites, thereby forming a continuous phase over the whole range of Nb concentrations. The Mossbauer spectra at 80 K fitted with a magnetic hyperfine field distribution show a continuous decrease of the average magnetic hyperfine field with increasing Nb concentration, as well as several different magnetic configurations forx≥0.3.

Magnetization and Mössbauer effect study of the pseudo-binary system (Ti 1- xNb x) Fe 2

Mössbauer spectroscopy, magnetization and X-ray diffraction measurements have been done on (Ti 1- x Nb x )Fe 2 compounds in order to investigate the effect of Nb on the magnetic properties of TiFe 2. The experimental results show that Nb enters the lattice by filling Ti sites thereby forming a continuous phase over the entire range of Nb concentrations. The Mössbauer spectra at 80 K fitted with a magnetic hyperfine field distribution show a continuous decrease in the average magnetic hyperfine field with increasing Nb concentrations as well as several different magnetic configurations for x ≥ 0.3. A similar result was obtained for the spectra at 10 K when samples with x ≥ 0.5 were fitted with a magnetic hyperfine field distribution. Magnetization measurements of M versus H for constant temperature and M versus T for constant magnetic field yield the following results: the pseudoternary compounds are antiferromagnetic in the concentration range 0 ≤ x ≤ 0.5 with the Néel temperature increasing slightly with Nb content up to x = 0.3 followed by a steady decrease as x increases to 0.5. Between x = 0.5 and 0.6 a magnetic phase transition from AF to ferromagnetism occurs. The spontaneous magnetization σ 0 increases with Nb content, reaching a maximum at x = 0.8. For larger Nb contents σ 0 decreases, going to 0 for the pure NbFe 2 phase. The Curie temperature shows behavior similar to that of σ 0.

A study on the preparation and magnetic properties of Fe 100−xB x ultrafine amorphous powders

By altering the preparation conditions, systematic variation of Fe 100− x B x ultrafine amorphous powders with 29 ≤x≤40 has been realized by the chemical reduction method. The preparation mechanism, the co-deposition of iron and boron atoms with boron atoms to stabilize the amorphous structure, was studied. The samples were characterized and investigated mainly by Mössbauer spectroscopy and differential scanning calorimetry. It is found that, with increasing boron contents in the samples, the average magnetic hyperfine field H decreases nearly linearly with a slope of about −4.7 kOe per B atom and the crystallization temperature shows a tendency, to increase. From the linear relationship of H vs. x, electron transfer from B to Fe was suggested. It is extrapolated that the powders will become paramagnetic when the B content reaches about 70 at.% and the H for pure amorphous iron is about 340 kOe, in nice agreement with the cases in amorphous ribbons.

Structural and magnetic properties of Nd2(Fe,Ti)19

Alloys with the composition Nd2(Fe,Ti)19 can exist in two crystal structures depending on the preparation technique. Melt-spun material has a hexagonal TbCu7-type structure (a=4.902 Å, c=4.248 Å) for a range of quenching speeds. Alloys prepared by arc melting, annealing at 1373 K and then water quenching have a complex monoclinic structure derived from a TbCu7 superlattice (a=10.644 Å, b=8.585 Å, c=9.755 Å, β=96.92°) and related to those of other intermetallics such as tetragonal Nd(Fe,Ti)12 and rhombohedral Nd2Fe17. Magnetic ordering temperatures for annealed (monoclinic) and melt-spun (hexagonal) Nd2(Fe,Ti)19 are 411 and 454 K, respectively. 57Fe Mössbauer spectroscopy at 295 K demonstrates that the local environments of the Fe atoms in the two structural modifications of Nd2(Fe,Ti)19 are similar. The average 57Fe magnetic hyperfine fields at 295 K for the monoclinic and hexagonal Nd2(Fe,Ti)19 are 20.8 and 22.3 T, corresponding to average Fe magnetic moments of 1.33 and 1.43μB, respectively.

Effect of C, Al and Si additions on the magnetic properties of melt-spun NdFeB alloys

We have studied the effect of the addition of C, Al or Si on the magnetic properties of NdFeB-based alloys crystallized from amorphous states. The amorphous Fe 77.5Nd 15(B 1− x M x ) 7.5 (M ≡ C, Al or Si and x = 0−1) alloys were prepared using the melt-spinning method. An increase in C content increases the remanence B r of Fe 77.5Nd 15(B 1− x C x ) 7.5 alloys crystallized at 873 K, and the maximum energy product ( BH)max is obtained as 93 kJ m −3 in the composition range x = 0.15−0.25. On addition of Al, the coercivity i H c is at a maximum (1.55 MA m −1) at x = 0.25. It is concluded from the variation of the relative intensities of the Mössbauer spectra that Al or Si atoms are preferentially substituted for one or two ( k 2 and probably j 2) Fe sites in the Nd 2Fe 14B phase. Mössbauer spectra show that C atoms occupy the same site as B atoms in the Nd 2Fe 14B phase and give a similar effect to that of B. The average magnetic hyperfine field of Nd 2Fe 14C is about 93% of that of Nd 2Fe 14B.

Photoemission and Mössbauer Effect Studies of Sputter‐Deposited Fe‐Pd Alloys

AbstractXPS core level and Mössbauer spectra of sputter‐deposited Fe‐Pd alloy films are studied. These films are composed of nonequilibrium b.c.c. and f.c.c. phases depending on the alloy composition. The core level spectra of Fe 2p and Pd 3d states reveal that the binding energy shift has a strong concentration dependence and the charge transfer between the constituent elements is appreciable. Mössbauer spectra at 290 K show that with increasing Pd concentration the average magnetic hyperfine field slightly increases in the b.c.c. alloys, whereas it decreases rapidly in the f.c.c. alloys.

Magnetic properties and hydrogen induced changes of amorphous Fe/sub 80/Cr/sub 10/Zr/sub 10/ alloys

The Mossbauer and magnetic measurements of as-prepared and hydrogenated amorphous Fe/sub 80/Cr/sub 10/Zr/sub 10/ alloys are carried out. The increasing of the average hyperfine magnetic field was observed. Both, the as-prepared and hydrogenated systems exhibit a ferromagnetic behaviour. >

Nd-Fe-BおよびNd-Fe-C系磁石合金に対する窒化処理

We have studied the effect of nitriding of Nd-Fe-B and Nd-Fe-C alloys by X-ray diffraction, Mössbauer spectroscopy, magnetization measurements and transmission electron microscopy. Samples were nitrided in an atmosphere of flowing NH3 gas at temperatures between 300 and 500°C.For the samples nitrided at 350, 375 and 400°C, interstitial dissolution of nitrogen atoms into Nd2Fe14B is assured by the extension of lattice constant of 0.2∼0.7%. Mössbauer spectroscopy shows that the increment of average hyperfine magnetic field of 57Fe in the Nd2Fe14BNx phase is 2∼4% as compared with that in the Nd2Fe14B phase. This is consistent with the result that the Curie temperature of Nd2Fe14BNx is about 20 degrees higher than that of Nd2Fe14B. The samples nitrided above 400°C are almost amorphous.Similar effects by nitriding, i.e. lattice expansion, increase in Curie temperature and that of hyperfine magnetic field, were also observed for Nd-Fe-C alloys.

A Mössbauer study of a new intermetallic phase Nd 2(Fe,Ti) 19 and its nitride

In this paper we present 57Fe Mössbauer spectra of a new ternary intermetallic phase Nd 2(Fe, Ti) 19 and its nitride. Our previous work suggests that the 2–19 phase is related to the hexagonal TbCu 7 structure. The average 57Fe magnetic hyperfine field of Nd 2(Fe, Ti) 19 at 295 K is 20.8 T which corresponds to an average Fe atomic magnetic moment of 1.33μ B. After nitrogenation, the average 57Fe hyperfine field at 295 K is 29.6 T, which corresponds to an average Fe atomic magnetic moment of 1.90μ B. This enhancement in the Fe atomic magnetic moment (at 295 K) is attributed mainly to the N-induced increase in Curie temperature of about 200 K.

Electronic and Magnetic Structure of B.C.C. FeMn Alloys

AbstractThe first principle discrete variational method in the local density approximation is employed to calculate the electronic and magnetic properties of 15‐atom clusters representing b.c.c. FeMn alloys. The occupation numbers and local densities of states are found to be unaffected by alloying in the case of paramagnetic clusters. When spin polarization is included the local magnetic moments at Fe sites are found to depend on the number of neighbouring Mn atoms and the FeMn coupling. The local moment components Eg and T2g at a site show different orientations. This is explained in terms of coupling T2g moments to nearest neighbours and of Eg moments to next‐nearest neighbours. The average magnetic moment and hyperfine field were calculated and compared with experimental data.

Magnetic hyperfine field distributions of amorphous FeB alloy particles and ribbons

Amorphous Fe 1− x B x alloy particles, prepared by a chemical reduction method, and ribbons, produced by the melt-spin method, have been investigated by Mössbauer spectroscopy. The average magnetic hyperfine fields and isomer shifts for ribbons and particles are found to resemble each other, but the hyperfine field distributions for the particles are significantly wider than for the ribbons. This indicates that the two types of alloys have slightly different amorphous structures.

液体急冷Ｎｄ‐Ｆｅ‐Ｃ系合金の磁気特性

We investigated the magnetic properties of meltspun Nd-Fe-C and Nd-Fe-C-B systems. The coercivity and (BH) max of Fe100-x(Nd2/3C1/3)x ternary alloys (x=17.5, 20, 22.5, 25) heat-treated at 800°C increased with a decrease in the Fe content. The (BH) max increased with the addition of boron to Fe77.5 Nd15 (C1-zBz)7.5 alloys. The Nd2Fe14C phase was clearly observed in the specimens, and an unknown ferromagnetic phase also appeared. The relative intensities and positions of the peaks of Mossbauer spectra led us to conclude that C atoms occupy the same sites as B atoms in the Nd2Fe14B phase and have a similar effect. The average magnetic hyperfine field of Nd2Fe14C is around 93% of that of Nd2Fe14B.

Mössbauer effect study on magnetic properties of intermetallic compounds (Sm 1—xY x) 2Fe 17N y

Mössbauer spectroscopy was used to study the substitution effect of Y for Sm atoms and the occupation of N atoms in (Sm 1—xY x) 2Fe 17N y ( x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0; 2 < y <3). Our results show that the N atoms in these nitrides occupy not only 9 e sites but also 3 b sites. The experimental results have confirmed the following facts. (1) The crystal structure changes when x exceeds 0.5. (2) The average magnetic hyperfine fields at the different iron sites in (Sm 1—xY x) 2Fe 17N y vary with the yttrium concentration. (c) (Sm 1—xY x) 2Fe 17N y compounds display an easy c axis anisotropy as the yttrium content ranges from x = 0 to 0.8 according to the Mössbauer fitting results.

Mössbauer effect study of the as-quenched, annealed and crystallised Fe 85−xCr xB 15 metallic glass

57Fe Mössbauer effect study of the as-quenched, annealed and crystallized Fe 85− x Cr x B 15 metallic glasses with x = 1, 3, 5 and 8 has been performed. The fitting of the room-temperature Mössbauer spectra of the as-quenched alloys shows that the values of both the most probable and average magnetic hyperfine fields decrease rapidly at a rate of 23 kOe per at% Cr. The magnetic hyperfine field distributions exhibit bimodal structure for the 8 and 10 at% Cr compositions. The opposite trend observed in the variation of the Mössbauer hyperfine parameters with annealing temperatures for the Fe 80W 5B 15 and Fe 80Cr 5B 15 metallic glasses may be due to the effect of different magnetic behaviours of W and Cr. It also implies that the dense random packing structure in the two alloys is different. Mössbauer effect studies of the alloys crystallised at 1073 K for an hour reveal the growth of the precipitated α-Fe and σ-(Fe, Cr) crystalline phases with increase of Cr concentration.

Mossbauer studies of ultrafine iron-containing particles on a carbon support

Carbon-supported metallic iron particles with an average diameter of 3.7 nm have been studied in situ by Mossbauer spectroscopy in the temperature range 5-305 K and with external magnetic fields up to 4 T. Depending on the preparation conditions various amounts of amorphous Fe-C particles are also formed. The average magnetic hyperfine fields of the surface atoms of alpha -Fe particles are significantly larger than that of bulk alpha -Fe at 5 K, but decrease much faster with increasing temperature than the bulk hyperfine field. The superparamagnetic blocking temperature for the alpha -Fe particles is about 70 K, but after oxidation it decreases to about 50 K, indicating that the magnetic anisotropy energy constant of the oxidized particles is significantly lower than that of the metallic particles. The temperature dependence of the spectral area is similar in the metallic and the oxidized states. In both cases the vibrational modes are dominated by particle vibrations.

Mössbauer-spectroscopy study of amorphous Fe-Ge alloys.

A M\ossbauer-spectroscopy study of amorphous ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$, with 0.11x0.72, was performed to measure the hyperfine-field parameters at 22 and 295 K. The distributions of quadrupole splitting suggest that for x0.2, the structure of the alloys is homogeneous and Fe atoms probably occupy the interstices of the Ge tetrahedral structure. For concentrations of xg0.4, however, hyperfine-field parameters seem to indicate that the alloys contain a mixture of short-range-order phases, with the average hyperfine magnetic field rising sharply with concentration. The resulting analysis of isomer shift, in terms of the model of Miedema and Van der Woude [Physica B 100, 145 (1980)], shows the Fe magnetic moment to be strongly influenced by hybridization and intra-atomic charge redistribution.

Surface magnetism in ultrafine α-Fe particles

Ultrafine particles of α-Fe have been studied by use of Mössbauer spectroscopy. The spectra contain a magnetically split component with broad lines which can be attributed to surface atoms. The average magnetic hyperfine field of this component decreases much more rapidly with temperature than that of the α-Fe core.