Critical exponent values at λ-transitions

The values of the critical exponents of a cooperative transition approached along different thermodynamic paths are in general different. The relations between these values are discussed and illustrated by application to decorated Ising lattices.     

Magnetic hyperfine fields in Y2Fe17−x Si x compounds

Y₂Fe_17–x Si _x compounds withx=0, 0.5, 1.0, 1.5, 2.0, 2.5 and3.0 were investigated by magnetic measurement andNMR. It is found that with increasing Si content the Curie temperatureT _C increases while the average Fe magnetic moment _Fe decreases. NMR study indicates that Si preferentially substitute the Fe atoms at 4f sites, which is responsible for the increase ofT _C.     

61Ni Mössbauer study of the surface hyperfine magnetic field in nickel

⁶¹Ni Mössbauer measurements have been performed at 4.2 K on spherical Ni particles with an average diameter of 100 and 30 Å, covered with a protective layer of SiO. Their spectra contain a surface component with a significantly reduced hyperfine magnetic field as compared with the field in the bulk. This result confirms recent theoretical predictions.     

Covalency and hyperfine structure of (3d)5 — Ions in crystal fields

A theoretical model is suggested which explains the dependence of the isotropic hyperfine interaction in ⁵⁵Mn²⁺ and ⁵⁷Fe³⁺ on a single covalency parameter.     

Critical dynamics of φ2n with random fields in the tree approximation

In the tree approximation, the critical relaxational dynamics of ²ⁿ with quenched random fields is calculated by renormalization near the upper critical dimensiond _u=4+2/(n–1). Although the relation between the characteristic frequency _c q and the wave-numberq is as usual,unusual results are obtained for the asymptotic decay of the order-parameter correlation functionS(q,t).Dedicated to Prof. Dr. W. Döring on the occasion of his 75th birthday     

Theory for position of muonium in α-quartz and associated hyperfine interaction

The electronic structures and hyperfine interactions of muonium and hydrogen in -quartz are investigated by the unrestricted Hartree-Fock cluster procedure. The muonium is found to be trapped near the center of the line joining two silicon atoms. On including vibrational effects, the muon hyperfine constant comes out as 1.09 times that for free muonium, this ratio being larger than unity and smaller than for protons in trapped hydrogen, both features being in agreement with experiment.Briefly reported in Abstract at the American Physical Society meeting in New Orleans, March 1988. See Bull. Am. Phys. Soc. 33 (1988) 770.     

Supertransferred hyperfine magnetic fields at111Cd(←111In) in ferrimagnetic oxides with the spinel structure

The supertransferred hyperfine magnetic fields,H _STHF, at¹¹¹Cd(¹¹¹In) on the tetrahedral sites of the spinel oxides Fe_3-xM_xO₄ (M = Ni or Co) were measured by means of the time differential perturbed angular correlation. The observedH _STHF were analyzed as the sum of the fields transferred from individual B site magnetic ions: 11 kOe/Fe³⁺, 8 kOe/Fe²⁺, 4 kOe/Ni²⁺ and 4 kOe/Co²⁺. A brief discussion is presented on these results in comparison with previous ones onH _STHF at¹¹¹Cd(^111mCd) in rocksalt-type oxides and the one at¹¹¹in in NiFe₂O₄.     

Effect of random magnetic fields on the hyperfine structure of Mössbauer spectra in paramagnetic single crystals

Under certain conditions, the⁵⁷Fe Mössbauer spectra of Al(NO₃)₃·9H₂OFe³⁺ single crystals exhibit new lines [1,2] (so-called z-lines) at an unusually high velocity of about 10.5 mm/s. The dependence of the positions and intensities of these z-lines on the magnitude and direction of an external magnetic field has been investigated. The appearance of the z-lines is explained by small random magnetic fields arising from magnetic nuclei in the crystal.     

Orientation of hyperfine magnetic fields of α-iron films produced by laser deposition

Iron films were produced by pulsed laser deposition (PLD) of iron in Ar gas and M?ssbauer spectra of these films were obtained at room temperature. The orientation of the hyperfine magnetic field was found to vary depending on the pressure of the Ar gas. Iron films produced at low Ar pressures exhibited magnetic fields parallel to the substrate surface. The magnetic field became increasingly perpendicular to the substrate with increasing Ar pressure. Collisions with Ar gas molecules reduced the translational energies of laser-evaporated iron atoms and thus the orientation of crystals formed on the substrate varied depending on the Ar pressure.     

Photon statistics measurement for coherent fields

An efficient scheme for photon statistics measurement is presented based on the Hanbury-Brown-Twiss configuration.We set the sampling time T_s to satisfy the relationship of T_s < T_d < T_m,where T_d is the dead time of each detector and T_m is the laser pulse repetition period.And each single photon detector cannot detect more than one photon in each pulse.The approach can sufficiently eliminate the influences of the detector's dead time on photon statistics.At last,the photon statistics of coherent field is experimentally determined.     

Spin alignment and Mössbauer hyperfine fields in the reentrant spin glass (Fe0.65Ni0.35)1-xMnx

Hyperfine Interactions - We performed Mössbauer spectroscopy on the ternary alloy system (Fe0.65Ni0.35)1-xMnx in applied external magnetic fields. From the hyperfine field distributions the...     

Inferring unresolved hyperfine structure in liquid solution EPR:14N hyperfine structure in the 1∶1 copper-calcimycin complex

Theoretical expressions for EPR line widths in liquids suggest the following two strategies for inferring unresolved hyperfine structure in near square planar copper(II) complexes and thereby identify the coordinating ligand atoms: (i) Increasing the resolution by reducing the line widths, by forming a mixed ligand complex of lower magnetic anisotropy. (ii) By demanding that the magnetic anisotropy determined from line widths, assuming unresolved hyperfine structure, should agree with that determined from frozen solution EPR spectrum.¹⁴N hyperfine structure from a coordinating cal (A _N ～ 12 G) in 1∶1 copper-calcimycin complex (Cu?cal) has been observed / inferred by the application of these strategies in 1∶1 chloroform-ethanol mixtures. It has been suggested that Cu?cal prepared in the presence of the bidentate ligand diethyldithiocarbamate (dtc^?) is the mixed ligand complex Cu(dtc)(cal) in which cal is a bidentate ligand. The Cu?cal prepared in the presence of a monodentate anion AN (AN=NO ₃ ^? , Br^?, Cl^? etc.) is Cu(AN)(cal) in which cal is a tridentate ligand. These complexes have near planar coordination geometry.     

Mössbauer measurement of hyperfine field in martensite

The dependence of the hyperfine field at ⁵⁷Fe nucleus in martensite on the carbon content by means of the Mössbauer effect was measured. This field is increasing relatively to that in α-Fe with the increase of % C the slope being (+1.5±0.2)% wt. % C.     

Theory of anisotropic hyperfine interactions in π-electron radicals

Anisotropic proton hyperfine interactions in π-electron radicals are approximated by a magnetic dipole interaction between each proton and an electron spin magnetization that is distributed in 2s and 2p Slater atomic orbitals centred on carbon atoms.     

Critical Hardy–Lieb–Thirring Inequalities for Fourth-Order Operators in Low Dimensions

This paper considers Hardy–Lieb–Thirring inequalities for higher order differential operators. A result for general fourth-order operators on the half-line is developed, and the trace inequality

Transfer matrix calculation of the exponent γ for two-dimensional self-avoiding walks

We develop two independent transfer matrix methods for the determination of the exponent in the two-dimensional, self-avoiding walk problem. Our first method is based on the calculation of the correlation length and uses conformal invariance. Our second method is based on the direct calculation of the moments of the order parameter distribution. Our results are in good agreement with the conjectured values.