Mössbauer studies and magnetic studies of Ni doped orthoferrites PrFe1−xNixO3 (x≤0.3)

The magnetic properties of polycrystalline PrFe_1−xNi_xO₃ (x≤0.3) system were studied using Mössbauer spectroscopy and magnetization measurements. The Mossbauer spectra exhibit six line spectra which loses its sharpness as the Ni substitution increases within the system. As the Ni concentration in the system increases, the hyperfine field and isomer shift shows decrease, which is vivid from the sluggish nature of the sextets. The small value of quadrupole splitting confirms the octahedral environment of the Fe⁺³ ions. The magnetization curves show the reversible behavior and represent the fall in negative molecular field leading to AFM frustration. From these results, we conclude that sagging in the spectra reveals the change from antiferromagnetic state to ferromagnetic state, which can be attributed to mixed state of Fe⁺³ ions i.e. high spin (HS) and low spin (LS) which is a consequence of progressive collapse of Hund’s rule due to HS→LS transition. These results confirm the weak ferromagnetic component due to canted-AFM spin arrangement of Fe³⁺ magnetic moments.     

Temperature dependence of the hyperfine field distribution in an amorphous ferromagnet

The rapid temperature decrease in magnetization characteristic of amorphous alloys is often attributed to short-range exchange interactions. The temperature dependence of the hyperfine field distribution in an amorphous Fe₈₀B₂₀ (METGLAS 2605) measured by Mössbauer technique disagrees with such an explanation. It is shown that for this alloy each magnetic moment follows the same magnetization curve, i.e. the temperature dependence of the magnetization is determined by long-range correlations.     

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.     

Ferromagnetic resonance of magnetic field oriented Fe3O4 nanoparticles in frozen ferrofluids

Measurements of the orientational dependence of the ferromagnetic resonance (FMR) spectra are made on Fe₃O₄ nanoparticles in ferrofluids solidified in dc magnetic fields. The in field solidification locks the direction of magnetization parallel to the direction of the cooling field enabling measurements as a function of orientation with respect to the direction of magnetization in the frozen state. The g value of the FMR spectra at 77 K is 2.16 and the anisotropy constant is −1.23 J/m³. A marked reduction of the difference between the field position in the parallel and perpendicular orientation onsets on warming to 140 K well below the melting temperature of the fluid carrier and is attributed to the onset of fluctuations in the direction of the magnetization in the solid phase. The phase transition of the magnetic symmetry observed in bulk Fe₃O₄ occurs at much lower temperature in the nanoparticles.     

Mössbauer studies of the irradiation effects of Y1.6Ca1.4V0.45Sn0.5Fe4.05O12

Y_1.6Ca_1.4V_0.45Sn_0.5Fe_4.05O₁₂ has been bombarded with a 0.56 GeV C⁶⁺ ion beam. The vacancies and vacancy clusters induced by the irradiation change the directions of hyperfine fields around the defects. The reduction of the magnetic hyperfine field is caused by the lower superexchnage field due to the formation of the O^2– vacancies. The change of direction of the hyperfine field has also been observed in Mössbauer spectra. X-ray diffraction showed that the defects give rise to an increase of the lattice constant of the samples.     

Magnetic and 57Fe Mössbauer studies of collinear spin rotation in Ho2Fe14B

Magnetic properties of Ho₂Fe₁₄B compounds have been studied by the ⁵⁷Fe Mössbauer effect and magnetization measurements. The axes of easy and hard magnetizations lie along the [001] and the [100] directions in the tetragonal structure, respectively, above T_sc = 58 K. From the comparison of the Mössbauer results with the magnetization measurements, it became clear that the Fe and the Ho moments tilt collinearly from the c-axis to the [110] direction throughout the temperature range of 4.2–58 K, and the canting angle reaches to 22° at 4.2 K. The Mössbauer spectra are consistently resolved with six subspectra above T_sc and with twelve below T_sc, together with reasonable site-assignments. We have estimated the mean Ho moment at 10.0μ_B, using the mean Fe moment of 2.3μ_B derived from the average hyperfine field or using the magnetization of Y₂Fe₁₄B as the Fe-sublattice magnetization of Ho₂Fe₁₄B.     

Influence of 50 MeV Lithium Ion Irradiation on Hyperfine Interactions of Cr0.5 Li0.5 Fe2O4

Spinel oxide Cr_0.5 Li_0.5 Fe₂O₄ has been irradiated at Nuclear Science Centre, New Delhi, by 50 MeV lithium ions of fluence 5*10¹³ ions/cm² and irradiation effect on hyperfine interactions has been investigated by Mossbauer spectroscopy. The Mossbauer spectrum of irradiated sample shows no paramagnetic doublet contribution and the hyperfine fields corresponding to the Fe³⁺ in the octahedral (B) and the tetrahedral (A) sites are very well separated. That is the observed superimposed A and B sites in unirradiated sample are split into separate lines after Li irradiation. Further an increase of the intensity of the lines (2)–(5) with respect to (1)–(6) signals an orientation of the hyperfine magnetic field towards a direction perpendicular to the ion path due to the irradiation induced strain by the latent tracks. The computer simulation of Mossbauer spectra indicated that the irradiated Fe³⁺-site occupancy of the A-site hyperfine field increased from 43% to 55% whereas the B-site hyperfine field decreased from 57% to 45% compared to unirradiated sample.     

Mixed hyperfine interactions and defect structure in magnesiowüstite Fe−Mg−O

An analysis of the 4.2 K spectra of Fe_xO (x∼0.91) and (Fe_0.4Mg_0.6)_xO is presented in which it is considered that because of the large electric field gradient at Fe²⁺ defect sites, the spectra cannot be described by Lorentzian sextets. It is assumed that the magnetic hyperfine field vector is oriented at random in the coordinate system defined by the EFG main axis, and that the EFG coordinate system is also distributed randomly. The simplifying assumption of the asymmetry parameter η=0 allows an analytical formula to be used to describe the complex spectra. Distributions of both magnetic hyperfine field and quadrupole interaction were progressively refined resulting in reasonable fits to the spectra with the main features being well reproduced. The magnetic hyperfine field distribution is rather broad with several features present while distinct values were obtained in the distribution of quadrupole interactions. These latter values are considered to correspond to the defect configurations around the Fe²⁺ sites. The distribution of hyperfine fields is considered to reflect the varying strengths of superexchange due to the high defect concentration as well as the effects of magnetic relaxation.     

Magnetization and Mössbauer studies of 57Fe doped SrCoO3

⁵⁷Fe (1%) doped SrCoO₃ obtained by high-pressure method, has been investigated by magnetization and Mössbauer spectroscopy studies (MS) in the temperature range 4.2 K to 300 K. The ferromagnetic ordering temperature T _C obtained is 272(2) K. Isothermal magnetization curves have been measured at various temperatures, from which the saturation moments (M _sat) have been deduced. The ⁵⁷Fe MS spectra display standard six-line patterns with an isomer shift typical of Fe^3?+? and a very small quadrupole splitting (QS = 0.14(1) mm/s above T _C). The magnetic hyperfine field at 4.2 K is 276(1) kOe. The temperature dependencies of the iron hyperfine field and M _sat (1.83 µ _B at 5 K) are almost identical. This shows that the Fe^3?+? is replacing Co^4?+?, both of the same electronic configuration. They also interact similarly, namely the Fe–Co exchange is almost identical to the Co–Co exchange.     

Magnetic properties of the garnets Bi0·8Ca2χT2·2-2.χFe5-χVχ]O12

The behaviour of the magnetization, Curie temperature, Mössbauer spectra, and lattice parameter is studied in the garnet series Bi_0·8Ca_2.χT_2·2-2.χFe_5-χV_χ]O₁₂. The shape of magnetization vs temperature curves shows only a minor dependence on x. The hyperfine field at the octahedral ⁵⁷Fe nuclei at 5°K decreases linearly with x (12·5kOe per substituted V neighbour), while that at the tetrahedral ⁵⁷Fe nuclei is not affected. The dependence of the Curie temperatures and hyperfine fields on x is discussed in relation to the Fe-O-V-O-Fe exchange. The influence of Bi substitution is consistent with the idea of a geometric effect.     

Mössbauer studies of electrodeposited Ni−Fe alloys

The magnetic texture and hyperfine field of Ni₁?_xFe_x alloys (0.141≤X≤0.648) obtained by electrodeposition around room temperature were studied by means of XRD and Mössbauer spectroscopy. A structural evolution from γ-phase (F. C. C.) to α-phase (B. C. C.) is observed with increasing Fe content. Concomitantly to the hyperfine field increase in the region a rotation of the preferred direction of magnetization is observed.     

Anisotropy of the magnetization and of the iron hyperfine field in R2Fe17 compounds

A single crystal of the hexagonal Y₂Fe₁₇ compound has been prepared. The exact composition, Y₂Fe_18.9 has been refined through X-rays measurements. A large anisotropy of the magnetization is associated with the large magnetocrystalline anisotropy. Mössbauer experiments have been performed at 4.2 K under high magnetic fields. A large anisotropy of the orbital contribution to the hyperfine field is reduced. This can explain the anomalies of the hyperfine field observed in Tm₂Fe₁₇ and ErFe₃ when magnetization reorientations occur with temperature.     

Magnetic properties and Fe NMR studies of U-type hexaferrites

U-type hexaferrites with compositions Ba₄Me₂Fe₃₆O₆₀ (Me=Cu, Fe, Co, Mn and Mg) have been synthesized and characterized by magnetization measurements and zero field ⁵⁷Fe nuclear magnetic resonance (NMR) spectra. The NMR spectra show resonance peaks corresponding to different crystallographic sites of iron (tetrahedral, octahedral and trigonal bipyramidal) with integral intensities according to their site multiplicity. In comparison with the NMR spectrum of M-type barium hexaferrite the intensities of some of the peaks arising due to iron sublattices (f_IV, a and b sites) are different, though there is no difference in peak positions indicating the same local hyperfine field strength at Fe nuclei. The maximum saturation magnetization at room temperature was found in Cu₂U (70 emu/g) and Fe₂U (67 emu/g). The Curie temperatures, saturation magnetizations and coercitivities for the U-type hexaferrites are given.     

Mössbauer studies of GdFe2 − x Hf x alloys

GdFe_2???x Hf _x alloys, where x?=?0, 0.10, 0.15, 0.20, and 0.30, are produced by arc-melting of pure elements. The samples are investigated by x-ray diffraction and Fe⁵⁷ Mössbauer spectroscopy at 78 K and 300 K. We find that the alloy system GdFe_2???x Hf _x have the single phase cubic Cu₂Mg type structure in the whole concentration range. Mössbauer spectroscopic results show that all the samples studied are magnetically ordered at 78 K, and at room temperature. The room temperature spectra are fitted with two magnetic components where the direction of magnetization is along the [111] while the spectra at 78 K are fitted with four magnetic subspectra indicating a complex direction of magnetization for all samples under investigation. The average magnetic hyperfine field and the average isomer shift are found to decrease almost linearly with increasing the Hf concentration at 78 K and 300 K due to the replacement of Fe by nonmagnetic Hf.     

激光辐照非晶Fe73.5Cu1Nb3Si13.5B 9微量晶化的穆斯堡尔谱研究

在激光功率为40—160W、扫描速度为10mm/s、激光光斑为20mm照射条件下,用CO ₂激 光辐照非晶Fe_73.5Cu₁Nb₃Si_13.5B_{9< /sub>产生微量晶化.利用透射穆斯堡尔谱 （TMS）技术分析了原始态和晶化后样品的超精细结构.确定了穆斯堡尔谱的基本参数——化 学位移(IS)、四极分裂(QS)、内磁场(Hhf)随激光功率变化的规律.分析表明，CO2关键词： 激光辐照 微量晶化 73.5Cu1Nb3 Si13.5B9')" href="#">非晶Fe73.5Cu1Nb3 Si13.5B9 穆斯堡尔谱}     

Magnetic ordering in a [Fe/Co]<Subscript>35</Subscript> BCC film studied by nuclear resonant reflectometry

An analysis of the angular dependences of nuclear resonant reflectivity time spectra for different models of magnetic ordering in films reveals an ambiguity in the magnetization direction determined from spectra measured at one orientation of the sample. This analysis explains features in the spectra of the nuclear resonant reflectivity from a MgO/[Fe(6 ML)/Co(3 ML)]₃₅/V (1 nm) film measured before and after sample rotation by 90° about the normal to the surface. It is shown that the spectrum measured only at one orientation of the sample determines only the effective azimuth angle of magnetization γ^eff. This does not exclude the occurrence of a domain structure, while the angle γ^eff does not correspond to the true direction of the preferred orientation of magnetization. The results of measurements at two orientations of the sample can be satisfactorily matched using a model that considers a coherent mixture of states with magnetization directed along the 〈110〉 axis (77%) and with a chaotic orientation of the magnetic hyperfine field B _hf in the film plane for the other nuclei.     

Mössbauer studies on Fe2MoO4

The Mössbauer spectrum of Fe₂MoO₄ at 4.2 K was fitted to two six line hyperfine patterns with field values of 218±5 k0e, due to Fe²⁺ on A-sites, and 414±5 k0e due to the presence of Fe²⁺, along with small amounts of Fe³⁺ on the B-sites. The spectrum with an applied transverse field of 50 k0e was fitted to three hyperfine patterns. The field values of these patterns suggest non-collinear spin arrangement in Fe₂MoO₄.     

A Mössbauer study of R6Fe13X (R=Pr,Nd; X=In,Sn, Tl,Pb, Cu,Ag, Au)

Compounds with the composition R₆Fe₁₃X (R=Pr, Nd; X=In, Sn, Tl, Pb, Cu, Ag, Au) were studied by⁵⁷Fe Mössbauer spectroscopy. Attention was focused on the influence of the easy axis of the magnetization on the shape of the hyperfine patterns. The spectra are composed of at least four subpatterns, originating from the different Fe lattice sites. Contrary to the magnetization, a significant dependence of the hyperfine parameters on the specific elements R and X could not be detected. Predominantly, the easy axis of the magnetization was found to lie within the basal plane; only for R=Nd and X=In, Sn, Tl, Pb is an easyc-axis present. Since the low temperature magnetization data obtained for the different compounds show a wide spread, while the⁵⁷Fe hyperfine fields remain almost constant over the whole series, some kind of antiferromagnetic ordering within the Fe sublattice is anticipated.     

Mössbauer studies of interstitial rare earth-iron intermetallics

Two series of interstitial rare earth-iron intermetallics, R₂Fe₁₇N_3-σ and R₂Fe₁₇C_3-σ have been prepared by gas phase reaction from the R₂Fe₁₇ parent compounds (R=Ce, Pr, Nd, ... Lu and Y). The interstitials raise the Curie temperature of the compounds by 390 K in the case of N and 330 K in the case of C. Mössbauer spectra at 15 K and 293 K, and data as a function of temperature for R=Er and Tm are analysed to yield hyperfine interactions at the four sites, and information on the local magnetization and its orientation. The change in hyperfine field is not proportional to the change in magnetization produced by the interstitials, being much greater in the nitrides than the carbides. Likewise for the isomer shifts. These effects are discussed in terms of the differences in electronic structure of the nitrides and carbides.