Low temperature pressure dependence of the muon hyperfine fields in iron,cobalt and nickel

The pressure dependence of the μ⁺ local magnetic fields in polycrystalline Fe and Ni and a Co single crystal has been measured at 77 K, up to 0.7 GPa, using a He gas high pressure setup. The pressure derivatives dlnB_μ/dP in units of mT/GPa are +4.4±1.0 (Fe), -0.7±1.1 (Co) and +0.63±0.10 (Ni). From these values the hyperfine field volume derivatives are deduced. Using these values together with previously determined room temperature derivatives the thermal expansion part of the temperature dependence of the hyperfine field can be calculated. The remaining explicit temperature dependence below 300 K, which deviates markedly from the temperature dependence of the bulk magnetization, is discussed.     

Mössbauer studies of dilute Au:Er alloys: Obervation of hyperfine structure of ground and excited CEF levels

The hyperfine structure of dilute ¹⁶⁶Er impurities in Au has been investigated between 1.8 and 60 K by Mössbauer spectroscopy. The hyperfine spectrum of the Γ₇ electronic ground state is clearly observed below 4.2 K while at higher temperatures there is an indication of the contribution from the excited CEF-states Γ⁽¹⁾₈ and Γ₆. Using Hirst's relaxation theory for the Γ₇ ground state the magnetic hyperfine coupling constant A=(247±3) MHz and the exchange coupling constant J_sf=(0.10±0.02)eV were derived. A quadruple coupling constant B of about 1 MHz was estimated from the hyperfine pattern of the Γ⁽¹⁾₈ quartet.     

Ferromagnetism in LiTbF4

The magnetic properties of crystals of tetragonal LiTbF₄ are reported for the first time. A transition to an uniaxial, high-anisotropy, ferromagnetic state is observed at T_c = 2.86 ± 0.03 K. The saturation moment is 8.90 ± 0.03 μ_B, close to the theoretical maximum of 9 μ_B for Tb³⁺. Magnetic dipolar interactions are shown to be large, and the effects of crystal fields are discussed.     

Hyperfine fields in erbium metal

The hyperfine Splitting of the 80.6-keVγ transition in Er¹⁶⁶ has been measured in erbium metal between 4.2 °K and 40 °K using the Mössbauer effect. There is evidence for a unique magnetic field and electric fieldgradient at all nuclei in erbium metal. The magnetic field decreases from (7.55±0.20)·10⁶ Oe at 4.2 °K to (6.10±0.40)·10⁶ Oe at 40 °K. Extrapolation to 0 °K yieldsH (0 °K)=(7.60±0.20)·10⁶ Oe. The quadrupole interaction energy for the 80.6-keV state iseQ V _Z′Z′/4=(0.95±0.20)·10^?6 eV at 4.2 °K. These results are discussed and compared with other measurements.     

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.     

Optical investigation of ErFeO3

The absorption spectrum of single crystals of ErFeO₃ has been investigated in the red and near infrared spectral region in the temperature range between 1.2 °K and 4.2 °K and at 20 °K and 77 °K. Between 77 °K and 4.2 °K a constant splitting of the absorption lines is observed. Below the Néel-temperature of the erbium sublattice at 4.5 °K the splitting of the absorption lines increases; the saturation value extrapolated to 0 °K of the splitting of the lowest crystal field level of the⁴ I _15/2 groundterm is (6.08±0.30) cm^?1. By measuring the Zeeman effect the groundstate magnetic moment is determined asμ=(6.6±0.2)μ _B. The measured temperature dependence of the splitting of the lowest crystalfield level of the⁴I_15/2 groundterm is compared with that calculated by a Monte Carlo method.     

NMR hyperfine spectrum of 143Nd in ferromagnetic cubic intermetallic NdAl2

The hyperfine spectrum of ¹⁴³Nd in NdAl₂ measured at T = 1.4 K provides values of ∣a_t∣ = 786 ± 0.5 MHz and ∣P_t∣ = 3.25 ± 0.03 MHz. The latter value is in agreement with the expected calculated value obtained from the 4f ground state wave function in a crystal field plus molecular field model, which may be deduced from inelastic neutron scattering experiments combined with susceptibility measurements, or from polarized neutron diffraction experiments. It is shown that the 4f electronic moment can be directly obtained from zero field NMR with good accuracy.     

Mössbauer study of a single crystal of RbFeF4

Mössbauer measurements taken between 1.4 and 300 K on a single crystal of RbFeF₄ show that below the Néel temperature of 133.8 K the hyperfine field is at an angle of 16.5 ± 0.5° to the principal axis of the electric field gradient tensor. The hyperfine field is seen to be along the [001] axis allowing the identification of the principal axis of the EFG with the shortest ligand of the tilted FeF₆ octahedra that are constituents of the crystal structure. At 300 K the ratio of recoil-free fractions (?_⊥/?_:) is measured as 0.96 ± 0.05 but at 77 K the measured ratio is 1.7 ± 0.2.     

59Co nuclear magnetic resonance in antiferromagnetic CsCoCl3

The ⁵⁹Co NMR in a CsCoCl₃ single crystal has been observed by the spin echo method at 4.2 K. The obtained spectrum is composed of seven distinct lines split by the nuclear-quadrupole interaction. The frequency of the central (± $\text{1}\text{2}$ ? ± $\text{1}\text{2}$) transition 502.08±0.05 MHz corresponds to the hyperfine field of 499.38 ± 0.05 kOe, which agrees well with the calculated value. Due to the interaction of the nucleus with the electronic moment induced by the external field, a shift as large as 18% was observed for the nuclear g-factor.     

X and K band ESR study of the Pb Interface centres in thermally oxidized p-type (001)Si wafers at low temperatures and influence of medium-dose As+ ion implantation

Electron spin resonance (ESR) experiments have been carried out at cryogenic temperatures (4.2 ? T ? 35 K) and room temperatures at 9.0 and 20.9 GHz on the P_b0 and P_b1 (commonly referred to as P_b) spin-active defects residing at the Si/SiO₂ interface. The ESR lineshapes were shown to display gaussian characteristics with inhomogeneous line broadenings amounting to 0.7 ± 0.1 and 0.2 ± 0.1 mT at K band for P_b0, and P_b1 respectively, whereas the oscillator strength of both signals followed the paramagnetic law (~ T^?1) down to 4.2 K within experimental error. In general the observed P_b spectrum appeared to have fewer peaks than in other observations, at most displaying two distinguishable lines. Mostly however, only one somewhat broad signal (of measured peak-to-peak linewidth >B_ptp ? 1.5 ± 0.15 mT and g = 2.0058 ± 0.0002 for $\text{\$}\text{?}$B 6 [001] was observed. By fully incorporating ΔB_ptp data for the first time in these observations and using computer simulations, it has been shown that the pervailing experimental spectrum always contains the signals from both kind of centers although mostly these are not separately discernable. Further, it emerged that the actual appearance of the experimental spectra is dirigated by the presence of a distribution of the SiIII unsaturated bond orientations around the ones normally prescribed by the Si crystallinity at the interface. It is found that for both centers this “angle” distribution predominantly occurs vertically with respect to the (001) interface plane. Ion implantation of 10¹⁴ As⁺ cm^?2 at 60 or 80 keV into the oxide layer of the Si/SiO₂ structure is shown to randomize the P_b dangling bond (DB) orientations (resulting in an isotropic g value behavior) but the effect of this is totally eliminated by subsequent annealing at 1000°C in N₂ ambient. It is argued that ESR has become a very sensitive means to study the “purity” of interfacial DB positions with respect to the Si single-crystal prescribed positions and to enable the display of collective fingerprints of the interface defects.     

Mössbauer Effect Study of Eu0.88Fe4Sb12 Skutterudite

The partly filled skutterudites Eu_0.88Fe₄Sb₁₂ were investigated by ⁵⁷Fe Mössbauer spectroscopy in the temperature range 4.2 K ≤ T ≤ 295 K and in external fields up to 13.5 T. The results favour a statistical distribution of Eu and voids in the Fe near neighbour shell. Below 82 ± 1 K magnetic order is present. Debye temperatures Θ _D = 460 ± 20 K and 165 ± 30 K were obtained for Fe with completely occupied Eu sites and for Fe with vacancies in the R-neighbour shell, respectively. The temperature dependence of the quadrupole splitting reflects the thermal expansion of the lattice. The induced hyperfine fields at 4.2 K are negative and differ by roughly a factor of two for the two Fe surroundings.     

EPR Study of the Vanadium Ions in Mg2SiO4 Crystal

Vanadium-doped forsterite crystal has been studied with X-band electron paramagnetic resonance (EPR) spectroscopy. The sample was grown by the Czochralski technique in an argon atmosphere with 2 vol% of hydrogen. The EPR spectrum of the sample at T = 15 K is predominantly represented by the V⁴⁺ ion signals that possess a characteristic eight-line hyperfine structure and are observed close to g = 2. The observation of the two magnetically nonequivalent centers in the angular dependence in the (ab) crystal plane and one center in the (ac) and (bc) planes, combined with the published optical spectroscopy data, unambiguously show that the V⁴⁺ ions are located at the silicon lattice site. Principal values of the hyperfine A and g-tensor and magnetic axes orientations of the V⁴⁺ centers have been determined. The orientation disorder of the V⁴⁺ centers has been found around the crystalline c axis but not in the (ab) crystal plane. The angular variation of the hyperfine component linewidth is described best with a disorder range of ±3.0°.     

237Np Mössbauer study of a novel intermetallic NpRh2Si2

NpRh₂Si₂ (ThCr₂Si₂ structure) has been studied by ²³⁷Np Mössbauer spectroscopy between 4.2 and 100 K. The isomer shift value suggest a Np⁴⁺ electronic configuration. A single site combined magnetic plus quadrupole pattern is observed up to the magnetic ordering temperature of T_c=73(1) K. A Np magnetic moment of 1.4μ_B is deduced from the hyperfine field measured at 4.2 K. The magnetic moments are estimated to make an angle of either 90° or 34° with the tetragonal axis.     

Polymorphism of anhydrous ferrous sulfate

The Mössbauer spectra of α-FeSO₄ and β-FeSO₄ have been measured in the temperature range 4.2 K ? T ? 30 K. The high temperature (β) phase is accompanied by a weak fraction of a third component. In analogy to CoSO₄, the third component of the three-fold polymorphism in anhydrous ferrous-sulfate is named the γ phase. X-ray powder measurements confirm this phase to be isomorphous to the corresponding γ-CoSO₄ structure. The parameters of the hyperfine interaction at 4.2 K of the three phases are evaluated. The magnetic ordering temperatures are T_N (α) = 24.0 K, T_N(β) = 17.0 ± 1.5 K and T_N(γ) = 19.5 ± 1.0 K.     

Etude par spectrometrie Mössbauer (57Fe) de FeMo2S4

We have investigated FeMo₂S₄ by transmission Mössbauer spectroscopy on the ⁵⁷Fe nucleus between 4.2 and 1037 K, using both powdered and single crystal samples.The temperature dependences of the isomer shift and the quadrupole splitting indicate the existence of ferrous ions with well localized 3d electrons. The two different crystallographic Fe sites cannot be separated over the experimental temperature range. The local symmetry of the iron site is lower than axial (η ~ 0.47) and the crystal field splittings Δ₁ and Δ₂ of the Fe²⁺ ? T_2g Orbitals, estimated by the Ingalls' method, are close to 250 and 900 cm^?1.The hyperfine field makes an angle of 14° with the normal on the plane (a, b), deviating a little from the direction of the magnetic moments determined to be perpendicular to (a, b) by neutron diffraction study.At higher temperatures, and more particularly near T_N, a line broadening is observed, and the spectra have to be fitted by a hyperfine field distribution. The broadening comes from the presence of about 7% “abnormal” Fe-sites observed in the paramagnetic spectra, and whose origin is discussed.The Néel temperature was determined to be 112 ± 1 K for the powdered sample and 106 ± l K for the single crystal.     

PrBa2Cu3O7−y investigated by141Pr Mössbauer spectroscopy

The¹⁴¹Pr Mössbauer isomer shift and hyperfine field spectrum of PrBa₂Cu₃O_7–y were measured at 25 and 4.2 K, respectively. The isomer shift corresponds to an intermediate valency of 3.4(1) and the hyperfine field spectrum at 4.2 K seems to indicate a hyperfine field of 29(3) T.     

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.     

On the determination of the structure of staurolite through mössbauer spectroscopy

Mössbauer studies are carried out on the powder and single crystal samples of staurolite silicate mineral at room temperature, 77 K and 4.2 K. The fitted hyperfine parameters are discussed in terms of staurolite structure. Our results suggest only one site for Fe²⁺ in the staurolite structure. V_zz is found at 45° to crystal a and c axes.     

Relaxation effects in Mössbauer spectra of bridged seven-coordinate Fe3+ pairs

The compound [Fe₂L(H₂O)₄] (ClO₄)₄.H₂O which contains pairs of Fe³⁺ ions within a binucleating macrocycle derived from Schiff base condensation of 2,6-diacetylpyridine and 1,3-diamino-2-hydroxy-propane has been studied by magnetic susceptibility measurements and⁵⁷Fe Mössbauer spectroscopy between 4.2 K and 300 K, and its crystal structure determined. The spectra show relaxation effects at all temperatures. Spectra taken at 4.2 K in applied fields of about 3 T showed thatV _zz is positive and η～0. The spectra were fitted using a stochastic model of a magnetic hyperfine field relaxing parallel to thez axis, giving relaxation times of 10^?9?10^?10 s.