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.     

Hyperfine magnetic fields in Fe−Co alloys and their tempera ture dependences

We obtained⁵⁷Fe hyperfine field parameters from Fe₁−x-Co _x alloys (0≤x≤0.6) from 77 K to 900 K. We first discuss the origin of the low temperature hyperfine fields in terms of the 3d and 4s electrons at⁵⁷Fe atoms. The⁵⁷Fe hyperfine magnetic field (hmf) of Fe-Co alloys depends more weakly on temperature than the hmf of pure Fe. This temperature dependence occurs because the alignment of the magnetic moments at both the Fe atoms and at the Co atoms depend on temperature in the same way as the bulk magnetization of Fe-Co alloys.     

Co/Cu multilayers studied by using the119Sn probe

To observe spin polarization in nonmagnetic layers sandwiched by magnetic layers,¹¹⁹Sn Mössbauer spectra of [Co(20 Å)/Cu(20-x Å)/¹¹⁹Sn(1.5 Å)/Cu(x Å)] (x=0, 5 and 10) multilayers were measured. A magnetic fraction is observed in every spectrum, and the average hyperfine field ¯H _f at Sn nuclei in a Cu layer changes from 14 kOe (x=0) to 8 kOe (x=10). It was also observed that the polarization is greatly reduced by adding a Cr layer of only 2 Å to the Co/Cu interfaces. The spectrum of thex=10 film, measured under an external field of 30 kOe, cannot be interpreted without assuming magnetic fractions both in parallel and antiparallel to the external field, which indicates an oscillation of spin polarization in a Cu layer.     

A Mössbauer spectroscopy study of SmTiFe11−x Co x

A series of SmTiFe_11?xCo_x compounds, where x ranges from zero to five, have been studied by⁵⁷Fe Mössbauer spectroscopy, x-ray diffraction, and related magnetic measurements. Random site occupation of Co atom occurs in SmTiFe_11?xCo_x when x>1. The Co concentration dependence of the magnetic hyperfine field for the samples, SmTiFe_11?xCo_x, and temperature dependence of the magnetic hyperfine field for SmTiFe₁₁ are obtained.     

The magnetic hyperfine field of lutetium in iron by NMR/ON

Nuclear magnetic resonance of oriented¹⁷⁷Lu in iron has been found with a sample prepared by on-line implantation of¹⁷⁷Lu in iron at T<0.2 K. The broad resonance, FWHM=20.5 (1.3) MHz, has a centre frequency of _L=355.06 (51) MHz at zero external field. With the g-factor of¹⁷⁷Lu g=0.637 (3) from literature the magnetic hyperfine field of Lu in Fe is derived as B_hf=–73.12(36) T. Static nuclear orientation data are not compatible with a two site model where the nuclei which are oriented experience the hyperfine interaction found in NMR/ON. A fraction with a lower hyperfine field is necessary to explain the data.     

Nuclear magnetic resonance of oriented54Mn nuclei in antiferromagnetic MnCl2 · 4H2O

Nuclear magnetic resonance of oriented⁵⁴Mn nuclei in antiferromagnetic MnCl₂ · 4H₂O has been observed. The first two lines of the sextuplet split by quadrupole interaction are at frequencies 500.4 and 514.7 MHz, implying a hyperfine field of 643(5) kG. The stronger line at 500.4 MHz has a half-width at half maximum of 60 kHz and is shifted downward and split in frequency on application of a magnetic field. The nuclear spin-lattice relaxation time is dependent both on the applied field and the size and/or quality of the crystal.     

Anomalous hyperfine field and orbital moment of cobalt in RCo2; R = Pr,Nd, Sm,Gd, Tb,Dy, Ho,Er and Tm

⁵⁹Co spin echo NMR spectra in the magnetically ordered phase of the MgCu₂ type RCo₂ compounds (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm) have been observed. For the RCo₂ with the easy direction of magnetication parallel to the 〈011〉 or 〈111〉 direction, the ⁵⁹Co hyperfine fields at two magnetically inequivalent Co sites are found to be antiparallel, revealing a large anisotropy in the ⁵⁹Co hyperfine field. The results are discussed in terms of a large and anisotropic orbital moment of Co. The transferred hyperfine field due to rare earth spins is estimated from well resolved satellite lines observed in Tb_1?xY_xCo₂. The nuclear quadrupole splitting in the magnetically ordered phase is found to be always larger than that in the paramagnetic phase.     

Transferred hyperfine fields at 119Sn in Fe1−xMxSn [M≡Mn, Co and Ni]

The transferred hyperfine fields at ¹¹⁹Sn, using Mössbauer spectroscopy are reported for the hexagonal B-35 compounds with a general formula Fe_1?xM_xSn, where MMn, Co and Ni. In these compounds, Sn atoms occupy two crystallographically inequivalent sites. For FeSn the observed spectrum consists of a quadrupole doublet and a magnetic pattern corresponding to 2(d) and 2(a) sites respectively. The data have been analysed to resolve the controversy regarding hyperfine parameters. On replacing Fe by Mn atoms, additional lines appear in the higher velocity region of the Mössbauer spectrum and the intensity of the nuclear Zeeman pattern increases at the expense of quadrupole doublet. The resulting Mössbauer spectra have been analysed by taking only the nearest neighbour interactions into account. This analysis shows that on replacing each Fe atom by a Mn atom, the hyperfine field at 1(a) Sn site increases by about 40 kOe and a field of about 35 kOe is produced at the 2(d) Sn sites. Further, from the nuclear Zeeman pattern for 2(d) sites, the sign of quadropole splitting for these sites could also be determined and was found to be positive. However, the substitution of Co and Ni in place of Fe atoms results in a broad unresolved pattern suggesting that the hyperfine field at the 1(a) sites decreases and a finite field develops at the 2(d) site. The origin of transferred hyperfine fields at the two inequivalent Sn sites is discussed, the magnetic transition temperatures of these compounds have been estimated and the magnetic moments of M-atoms have been inferred.     

Mössbauer effect studies of Tb<Subscript>0.27</Subscript>Dy<Subscript>0.73</Subscript>(Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)2 intermetallics at 295 K

The synthesis of materials and the studies of crystal structure and ⁵⁷Fe Mössbauer effect were performed for Tb_0.27Dy_0.73(Fe_1?x Co _x )₂ intermetallics. Terfenol-D (Tb_0.27Dy_0.73Fe₂) is the starting compound of this Fe/Co-substituted series. X-ray measurements showed evidence of a pure cubic Laves phase C15, MgCu₂-type, and unit cell parameters were determined across the series. A Co substitution introduced local area, at sub-nanoscale, with random Fe/Co neighbourhoods of the ⁵⁷Fe atoms.Mössbauer effect spectra for the Tb_0.27Dy_0.73(Fe_1?x Co _x )₂ series at room temperature are composed of a number of locally originated subspectra due to the random distribution of Fe and Co atoms in the transition metal sublattice, and due to [1 1 1] an easy axis of magnetization. Isomer shift, magnetic hyperfine field and quadrupole interaction parameter were obtained from the spectra, both for the local area and for the bulk sample.As a result of Fe/Co substitution, a Slater-Pauling-type curve for the average magnetic hyperfine field vs. Co content was observed. It was found that the magnetic hyperfine fields corresponding to the local area also create a dependence of the Slater-Pauling-type vs. Co contribution in the Fe/Co neighbourhoods.     

Hyperfine interactions and local magnetic ordering in Zr(Fe1-xCox)2 (0⩽x⩽0.2)

In the pseudobinary intermetallic compounds Zr(Fe_1-xCo_x)₂ (0?x?0.2) the hyperfine fields of all nuclei present are investigated by means of Mössbauer effect and NMR. While for the “nonmagnetic” site the Zr-hyperfine field depends on the configuration of the nearest Fe, Co neighbours, no such effect is observed for the hyperfine fields on the “magnetic” sites. A large pseudodipolar interaction is observed for the Fe and Co atoms, from which the coexistence of several directions of magnetization can be deduced. The easy direction seems to be determined by the respective Fe/Co configuration.     

Influence of radiation damage on the hyperfine field of triton irradiated nickel foils

The recently observed Mössbauer effect in⁶³Ni enables the study of the hyperfine field in nickel with high resolution. In the present paper, the line broadening of the Mössbauer resonance is analyzed in order to study the influence of radiation damage on the magnetic hyperfine field in⁶⁴Ni foils. Each of these foils was irradiated by tritons at 15 K with a total current integral of 2.4 A h in order to produce the short-lived⁶³Co sources (T _1/2=27 s). An upper limit of 4.6 kG was estimated for the standard deviation of the magnetic hyperfine field distribution which resulted from the accumulated radiation damage. For the annealed absorber material the standard deviation of the magnetic field is less than 53 G.     

Magnetic Moment of the 3/2− Ground State of 185W

Nuclear magnetic resonance measurement have been performed for ¹⁸⁵W oriented at 8 mK in an Fe host. The magnetic hyperfine splitting frequency at an external magnetic field of 0.1 T was determined to be 196.6(2) MHz. With the known hyperfine field of B _hf = −71.4(18) T, the nuclear magnetic moment of ¹⁸⁵W is deduced as μ(¹⁸⁵W) = +0.543(14) μ_N.     

Nuclear magnetic resonance of175Hf oriented in iron

Nuclear magnetic resonance of¹⁷⁵Hf oriented at low temperature in iron has been observed with a sample prepared by ion implantation. The centre frequency of the broad resonance line isv _L (B _ext = 0)=138.53(36)MHz. Possible origins of the large inhomogeneous line width of FWHM=11.0(1.1) MHz are discussed. A comparison with model calculations for combined magnetic and electric hyperfine interaction indicates that the centre frequency may be interpreted as the magnetic interaction frequency for¹⁷⁵Hf in unperturbed substitutional sites of the host iron. With theg-factor of¹⁷⁵Hf from literature the magnetic hyperfine field of Hf in Fe is derived asB _hf=?64.9(9.3) T fitting well into systematics.     

Magnetic hyperfine interaction of 59Fe in nickel

Nuclear magnetic resonance on oriented nuclei (NMR-ON) on ⁵⁹Fe isotope in Ni was performed. The magnetic hyperfine splitting frequency of was determined to be ν(B ₀?=?0)?=?48.32 (2) MHz. Using the known magnetic moment the magnetic hyperfine field was deduced as B _HF?=???28.32 (5) T. The effective nuclear spin-lattice relaxation time was also measured. The measured value is compared with experimental values of 3d-impurity in nickel host.     

Magnetic behaviour of NpAs2 from Mössbauer spectroscopy

The Mössbauer hyperfine spectra of the 60 keV resonance of ²³⁷Np in powder and single crystal absorbers of NpAs₂ were measured between 4.2 and 60 K. Below 18 K a simple magnetic plus quadrupole pattern is seen in accordance with a ferromagnetic spin structure in tetragonal NpAs₂. The isomer shift favors the 4+ charge state, the hyperfine field of 288 T implies a moment of 1.5μ_B at the Np ion. The large reduction compared to the free ion values points towards a strong mixing of the electronic ground state by crystalline field interactions. Above 18 K the spectrum changes into a complex hyperfine pattern indicating a sinusoidally modulated spin structure. Near 54 K a transition into the paramagnetic state is observed. Both magnetic transitions (18 and 54 K) exhibit a feature typical for a first-order character.     

The supertransferred magnetic hyperfine field in chromium-iron tellurates

The broadening of the¹²⁵Te Mössbauer spectral absorption with decreasing temperature in compounds of the type Cr_2?x Fe _x Te _x TeO₆ (x=0.4, 0.8, 1.0, 1.5) is attributed to the presence of a supertransferred magnetic hyperfine field. The origin of the supertransferred magnetic hyperfine field, which is not observed in antiferromagnetically ordered Cr₂TeO₆ or Fe₂TeO₆, is associated with an imbalance in the magnetic exchange interaction at tellurium which results from the replacement of chromium by iron.     

Helimagnetism in gallium substituted LuMn<Subscript>6</Subscript>Ge<Subscript>6</Subscript> studied by nuclear magnetic resonance

Zero-field nuclear magnetic resonance (NMR) of all NMR isotopes (¹⁷⁵Lu, ⁵⁵Mn, ⁷³Ge, ^69,71Ga) in LuMn₆Ge_6-xGa_x, 0 ≤ x ≤ 1, is used to monitor the variation of the hyperfine interaction with the sequence of antiferromagnetic - helimagnetic - ferromagnetic arrangement of the manganese moments of subsequent Kagomé net planes achieved by variation of the gallium content x. According to the ⁵⁵Mn-NMR results, the local Mn moment varies by less than ±5% in this series. ¹⁷⁵Lu-NMR proves canting of the antiferromagnetic sublattices in LuMn₆Ge₆. The anisotropy of the Ge magnetic hyperfine interaction decreases with increasing separation from the hexagonal Lu plane, whereas the absolute value of its isotropic part is only qualitatively correlated with the average separation of the six nearest Mn neighbours. Due to the anisotropic magnetic and electric hyperfine interaction at Ge and Ga sites, the non-collinear magnetic structures are clearly reflected by the NMR spectra, which are described quantitatively in this contribution. The preferred Mn moment direction rotates away from the c direction with x. The conduction or bonding electron spin polarization at the Ga nuclei is increased by 35–80% compared to the Ge nuclei. We argue that this is related with the variation of the magnetic order with the Ga content.     

Nuclear magnetic resonance of RCo3(R:Rare earth)

The nuclear magnetic resonance of⁵⁹Co nuclei in magnetic domains of RCo₃(R:Y, Nd, Sm, Gd, Tb, Dy and Ho) has been measured under external fields up to about 50 kOe at 4.2 K. To assign the observed NMR signals to each Co site, the⁵⁹Co nuclear magnetic resonance of R(Co_1−xNi_x)₃ and R(Co_1−xFe_x)₃ has also been measured under the same conditions. The results of NMR studies show that the cobalt atoms at the 6c site in the light R compounds(YCo₃, NdCo₃ and SmCo₃) and these at the 3b site in the heavy R compounds(GdCo₃, TbCo₃ and HoCo₃) have a large orbital contribution.     

59Co nuclear magnetic resonance study in GdCo2Si2 compound

The spin echo NMR spectra of⁵⁹Co for GdCo₂Si₂ are reported. A weak negative hyperfine field on Co nuclei was found in magnetically ordered state of the compound. The splitting of resonance lines in external magnetic field indicates on antiferromagnetic structure of Gd moments lying in thea-a plane with energetic minima in [100] and [110] directions as in GdFe₂Si₂ and GdNi₂Si₂.