Mößbauereffekt in Eisenstilben und FeCl2·H2O

Using Mößbauer effect measurements in the temperature range between 3 °K and 310 °K the magnetic fields at the nucleus in iron-stilbene, FeCl₂·H₂O and FeCl₃ are determined to beH _T=0=(250±10) kOe, (252±18) kOe and (468±10) kOe; a Néel-temperature ofT _N=(23±1) °K is measured for iron-stilbene. The electric quadrupole splittings atT=0 °K for iron-stilbene and FeCl₂ ·H ₂ O, ΔE=(+2.52±0.02) mm/sec and (+2.50±0.05) mm/sec, yield electric field gradients at the iron nucleus ofq _z=+9.7·10¹⁷ V/cm² and +9.6·10¹⁷ V/cm², whereq _z⊥H; Debyetemperatures of θ=162 °K and 188 °K are obtained. The energy of the excited 3d-electron levels in iron-stilbene is estimated to Δ₁=309 cm^?1 and Δ₂=618cm^?1 as deduced from the temperature dependence ofΔE. In contrast to the suggestion ofEuler andWillstaedt bivalence of the iron in ironstilbene is found; its composition is shown to be 4(FeCl₂ ·H ₂O)·stilbene.     

Optical spectroscopy of Dysprosium Aluminum Garnet (DAG)

The absorption spectrum of antiferromagnetic dysprosium aluminium garnet (DAG) (T _N =2.50 °K) has been investigated at low temperatures. The groundstate splitting due to all interactions in the antiferromagnetic state is (5.27±0.10) cm^?1 extrapolated to 0 °K. The temperature dependence of the lineshift of the absorption lines is measured. Zeeman effect studies give theg-tensor of the groundstate asg _z =18.4±0.5,g _x =g _y =0.5±0.2. The studies also allow the determination of the critical fields asH _c ^[100] =(5.0±0.1) koe,H _c ^[111] =(3.9±0.2) koe andH _c ^[110] =(4.9±0.6) koe. In addition an investigation of a number of satellite lines is performed. Some of them can be interpreted as spin wave sidebands (Stokes and anti-Stokes); others obviously come from dysprosium ions which have impurity ions on regular lattice sites as neighbours.     

γ-Detected NMR of103 mRhFe

Using the method ofγ-detection, the NMR in the metastable 40 keV-state of¹⁰³Rh in Fe (thin foils with diffused¹⁰³Pd activity) was measured in external fields of 0.5 to 14 kG. We find a zero-field resonance frequency ofv ₀=(550.3±0.5) MHz and a slope ofdv/dH= ?(0.933 ±0.017) MHz/kG, yielding g=1.22 ± 0.02. The resulting value for the hyperfine field, H_hf=(590±10) kG, is inconsistent with that of an NMR measurement in the ground state of¹⁰³Rh. Possible reasons for this discrepancy are discussed.     

Relaxation des Natrium-Grundzustandes bei Stößen mit den stabilen Helium- und Wasserstoff-Isotopen

The spin-polarization of the optically pumped Na-groundstate is investigated in presence of the stable He- and H₂-isotopes. The following disorientation cross sections are derived from the pressure dependence of the relaxation rate:σ=(16.2±2.0) · 10^?26 cm² for He³ σ=(2.4±0.5) · 10^?26 cm² for He⁴ σ=(3.9±1.5) · 10^?26 cm² for H₂ σ=(2.3±1.0) · 10^?26 cm² for D₂. These values can be compared with theoretical cross sections based on two relaxation models and indicate the existence of a relaxation mechanism involving the exchange of the electronic alkali-spin with the nuclear spin of the foreign gas.     

Mößbauereffekt in FeCl2, FeSO4 und FeSO4 · 7 H2O

Mößbauereffect measurements were performed with FeCl₂, FeSO₄ and FeSO₄ · 7 H₂O in the temperature range between 5 and 300 ?K. The quadrupole splittings at 5 ?K were determined to be (1.300±0.027) mm/sec, (3.650±0.053) mm/sec, and (3.350±0.053) mm/sec respectively. From the temperature dependence of the quadrupole splittings it follows that in FeCl₂ the energy of the excited 3d-electron-level isδ=150 cm^?1, in FeSO₄ δ ₁=360 cm^?1 andδ ₂=1680 cm^?1 and in FeSO₄ · 7 H₂Oδ ₁=480 cm^?1 andδ ₂=1300 cm^?1. The magnitudes of the magnetic field at the iron nucleus at 5 ?K are (202±8) kOe for FeSO₄ and (0±4) kOe for FeCl₂.     

EPR of Fe3+ ion and symmetry of [AIF5·H2O]2? complex ion in (NH4)2AIF5·H2O single crystals

We used the spin-Hamiltonian method for the analysis of the electron paramagnetic resonance (EPR) spectrum of Fe³⁺ as a probe ion in (NH₄)₂AlF₅·H₂O single crystalline basic material. The theoretical expressions for the magnetic field (at which the fine structure transition lines appear) versus the angle between the magnetic field and the axis of symmetry of the magnetic complex are also given. These values were calculated by applying the perturbation theory to the second-order terms. From the experimental results (at 300 K and 9.21 GHz), the spin-Hamiltonian parameters were deduced:D=(668±10)·10⁻⁴ T,E=(−56±10)·10⁻⁴ T,a=(−54±10)·10⁻⁴ T,F=(30±10)·10⁻⁴ T. An isotropic superhyperfine structure was evidenced for the five fluorine ions. The obtained EPR data were used to determine the local symmetry of the Al³⁺ ion. A good agreement with X-ray diffraction measurements was found.     

Magnetic transitions in K2MnCl4·2H2O

Results of (dM/dH) measurements on tetrahedral K₂MnCl₄·2H₂O as a function of temperature and magnetic field, are presented. An antiferromagnetic transition along the tetragonal axis is observed at T_N = (3.05±0.05) K. The H-T magnetic phase diagram was completely determined, and shows the usual characteristics of that of a low anisotropy antiferromagnet. The T = 0 critical fields are compatible with the values H_E = (29.2±0.3) kOe and H_A = (5.9±0.6) kOe for the exchange and anisotropy fields.     

Crystalline fields,exchange interactions and spin reorientations in TmxHo1−xFe2 systems,studied by a Yb170 Mössbauer probe

Mössbauer studies of the 84.3 keV gamma ray of Yb¹⁷⁰ emitted from Yb in Tm_xHo_1?xFe₂ at various temperatures were performed. These yield the crystalline field parameters (A₄〈r⁴〉 = 36 ± 5 K, A₆〈r⁶〉 = -3 ± 2K, the exchange field (μ_BH_exch = 116 ± 4 K) and the Yb³⁺ free ion hyperfine constants (H_4f = 4100 ± 150 kOe, eqQ = 2400 ± 250 MHz and H (conduction electrons) = 350±100 kOe). Spin relaxation phenomena observed in TmFe₂ at low temperatures give a value of ～ 0.03 for |?(E_F)J_sf|. Spectra observed in Tm_0.2Ho_0.8Fe₂ in the spin reorientation transition region indicate that the transition is of second order.     

Das magnetische Moment des 2,083 MeV-Zwei-Protonen-Niveaus des gerade-gerade-Kerns Ce140

The nuclearg-factor of the 2·083 MeV-state of Ce¹⁴⁰ has been determined as:g=1·11±0·04 This value suggests the interpretation of the level as the (g7/2,d5/2)₄ two proton shell model configuration. The investigation implies an integral measurement as well as a time dependent differential measurement (spin rotation method) of the rotation of the 329 keV-487 keVγγ-angular correlation in strong external magnetic fields. Liquid sources of lanthanum nitrate solved in 3n HNO₃ were used in these experiments. Some cerium (IV)nitrate was added to make sure that the 4f;-electronic shell remained empty after theβ ^?-decay. This prevented paramagnetic effects. Additional runs were performed without adding cerium (IV)nitrate and finally by using liquid sources of lanthanum chloride solved in 2n HCl with some iron (II)-chloride added. It was expected that the Fe⁺⁺ ions would reduce the primarily formed Ce⁺⁺⁺⁺ ions into the Ce⁺⁺⁺ state. The Ce⁺⁺⁺ shell is paramagnetic and enlarges the effective magnetic field at the position of the nucleus by about 36%. As no definitely faster rotation could be observed, one has to conclude that the ion reaction Ce⁺⁺⁺⁺+Fe⁺⁺?Ce⁺⁺⁺+Fe⁺⁺⁺ takes more than about 10^?8s. The half life of the 2·083 MeV state has been redeterminded asT _1/2=(3·41±0·04)·10^?9s. Differential measurements of the angular correlation of the 329 keV-487 keV cascade as a function of the time delay showed that perturbations by internal fields were very small. The coefficientsA ₂ andA ₄ of the angular correlation and the attenuation parameterλ ₂ were determined from measurements with sources of the first type as:A ₂=?0·105±0·003A ₄=?0·001±0·002 andλ ₂=(0·0065±0·0040)·10⁹S^?1=(0·032±0·020)·λ A comparison with the theoretical coefficients of a (3-4-2)-cascade shows that the multipolarity of the 329 keV radiation is a mixture of 99·83%M1 and (0·17±0·03) %E2.     

Hyperfine fields on Hafnium nuclei in iron and gadolinium metal

The recoil implanation perturbed angular correlation technique, IMPACT, has been used to study the hyperfine interaction in¹⁸⁰Hf in iron and gadolinium. The perturbed angular correlation through the Coulomb excited 4⁺ state was used, thus minimizing the effect of quadrupole interactions. The effective hyperfine fields on Hf in iron and gadolinium are determined to have the same sign,negative, and magnitudes of (507±60) kOe and (304±31) kOe, respectively. Results are compared with values reported from several other experiments ostensibly measuring the same quantity. Problems inherent in the various experimental techniques are considered.     

Nuclear magnetic resonance of 131I and 132I oriented in Fe

Nuclear magnetic resonance has been applied to radioactive I nuclei oriented in Fe. By field shifting the ¹³¹I resonance the hyperfine field is determined as positive. The ¹³¹I resonance at 683.3 ± 1.0 MHz and the ¹³²I resonance at 674.0 ± 0.5 MHz give H_int = 1144.0 ± 1.5 kOe.     

Untersuchung gestörter Winkelverteilungen an F19 in ferromagnetischen Gittern

The perturbation of the 197 keV transition angular distribution in F¹⁹ was investigated by time-dependent spin rotation measurements following excitation with a pulsed beam. The recoil implantation technique was used to determine the internal magnetic fields for F¹⁹ in Fe, Co and Ni lattices. The results are:H _HF(F¹⁹ in Fe)=+(95700±500) Oe,H _HF(F¹⁹ in Co)=+(59500±1500) Oe,H _HF(F¹⁹ in Ni)=?(21830±350)Oe. The temperature and field dependence of the effective fields was studied. Strong satellite fields due to lattice perturbations were detected. The half life and the gyromagnetic ratio of the 197 keV 5/2⁺ state in F¹⁹ were redetermined asT _1/2=(80.2±0.5) nsec andg=+1.436±0.007.     

Magnetic collapse in yttrium iron garnet Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> at high pressure

The effect of high pressures up to 70 GPa on single-and polycrystalline samples of yttrium iron garnet Y₃⁵⁷Fe₅O₁₂ is studied by Mössbauer absorption spectroscopy (for the ⁵⁷Fe nucleus) in a diamond-anvil cell. It is found that the hyperfine magnetic field H_hf at ⁵⁷Fe nuclei vanishes abruptly at a pressure of 48 ± 2 GPa, which indicates the transition of the crystal from the ferrimagnetic state to nonmagnetic one. The magnetic transition is irreversible. When the pressure decreases, the magnetic state is not recovered and the garnet remains nonmagnetic until zero pressure. The behavior of the quadrupole splitting and isomer shift shows that, simultaneously with the magnetic transition, irreversible electron and possibly spin transitions occur with changes in the local crystalline structure. The mechanisms of the magnetic collapse are discussed.     

Phenomenological analysis of the linear magnetic birefringence in dysprosium iron garnet

Experimental data on linear magnetic birefringence (LMB), previously reported at 1.15 μm wavelength in the 4.2-300 K temperature range and with an applied field up to 20 kOe, in dysprosium iron garnet (DyIG) are analyzed in terms of electric dipole transition within the three magnetic sublattices. Assuming that the garnet symmetry is cubic and that the contribution of the Fe³⁺ ions to LMB is the same as yttrium iron garnet (YIG), the 2nd order magneto-optical (MO) coefficient (Γ₂) of the Dy³⁺ ions is deduced. In the spontaneous state, Γ₂ is linear temperature dependent as previously found for the 1st order (MO) coefficient. It is shown that Γ₂ must be field dependent to explain the evolution of the LMB.     

Multihadronic decays and partial widths of the J/Ψ (3100) resonance produced in e+e− annihilation at adone

The reactions e⁺e^?→ hadrons and e⁺e⁺e^?→e⁺e^? have been studied at the J/gY (3100) resonance). The relative weights of the topological cross sections for fixed charged multiplicity are σ₂=(32±5)%, σ₄=(49±8)%, σ₆=(18±3)%, and σ₈=(1±0.6)%. The average pion multiplicities are 〈n_ch〉=3.8±0.3 and 〈n_{π^o〉=3.1±0.8}. The decay widths are Γ_e=(4.6±0.8) keV, Γ_h=(59±24) keV, and Γ=(68±26) keV.     

The upper critical field of superconducting polysulfur nitride, (SN)x

A measurement of the temperature and angular dependence of the upper critical magnetic field H_c² in crystals of polymeric (SN)_x is reported. A large anisotropy is observed at all temperatures with H_c²6 = 8.1 ± 0.4 kOe parallel to, and H_c²⊥ = 870 ± 80 Oe perpendicular to, the polymer axis at 0°K. The results are explained in terms of the polymeric crystal structure and fibrous morphology of (SN)_x.     

Die Hyperfeinstruktur des 32P3/2-Zustands von Natrium im starken Magnetfeld

The hyperfine structure of the 3²P_3/2 State of Na²³has been measured by the optical double resonance technique in a magnetic field of 3.1 kG sufficiently strong to decouple completelyI andJ. In the case of π or (σ⁺+σ^?) excitation the double resonance signal represents the superposition curve of eight unresolved radio-frequency transitions. The dependence of the signal on the pressure of sodium vapour and the radio-frequency field strength has been studied. The analysis of the experimental curves yields for the hyperfine coupling constants the valuesa=(18.7±0.4) Mc/s andb=(3.4±0.4) Mc/s. The nuclear electric quadrupole moment derived from the ratio ofb/a isQ=(0.146±0.02) · 10^?24cm². The Lande factor and the lifetime for the 3²P_3/2state are g_J=1.3344±0.0004 and τ=(1.61±0.07) · 10^?8 sec.     

Bestimmung der Atomspinkorrelationszeiten der Fe3+-Ionen in FeNH4(SO4)2·12 H2O mit Hilfe des Mössbauereffektes

The Mössbauer effect studies of⁵⁷Fe in the paramagnetic salt FeNH₄(SO₄)₂·12 H₂O reported byObenshain et al. were extended to higher values of the applied external magnetic fieldH _a. The results are discussed in terms of the theoretical calculations given byWegener. The data can be fitted using a maximum internal fieldH _max=(598±10) kOe and two atomic spin correlation times τ_c=2,4 · 10^?9 sec andτ′ _c=2,1 · 10^?9 sec.τ _c andτ′ _c are independent ofH _a and the temperatureT. It is assumed in the analysis that the distribution w(H) of the internal fields can be described by a continuous function of the Boltzmann factor type with two parameters. These two parameters are determined by the normalization and the macroscopic magnetization.     

Static electric quadrupole interaction of Ta- and Hf-ions in barium and lead titanate

The static electric quadrupole interaction of¹⁸¹Ta and¹⁷⁸Hf in polycrystalline barium and lead titanate at the site of titanium has been measured using time differential PAC and the Mössbauer effect. The electric field gradients (EFG) at room temperature at the¹⁸¹Ta nucleus are ¦V _zz¦=(3.6±0.2)·10¹⁷V/cm² in BaTiO₃ and ¦V _zz¦=(14.6±0.6)·10¹⁷ V/cm² in PbTiO₃. The temperature dependence of the quadrupole interaction has been studied giving the following EFG values: ¦V _zz¦=(2.4±0.2)·10¹⁷ V/cm² in the monoclinic and ¦V _zz¦=(1.1±0.3)·10¹⁷ V/cm² in the rhomboedral phase of BaTiO₃, and ¦V _zz¦=(15.7±0.6)·10¹⁷ V/cm² for¹⁸¹Ta/PbTiO ₃ at 77 °K. The EFG of¹⁷⁸Hf in PbTiO₃ has been derived from a Mössbauer effect experiment to beV _zz=+(10.7±0.5)·10¹⁷ V/cm². The results are compared with EFG's calculated in a point charge model and with experimental EFG's measured at⁴⁴Sc and⁵⁷Fe in the same titanates by other authors. Contributions of covalent bonds to the effective EFG's in perovskit crystals are discussed.