B. Lindgren

The effect of pressure on the positive muon spin precession in iron and nickel

Abstract We have determined the pressure dependence of the local magnetic fields at μ + sites to be: ( ∂ In B / ∂p ) 298K = -1.05 (2) × 10 -3 /kbar for Fe, +0.43 (6) × 10 -3 /kbar for Ni. The dependence on temperature (also measured here) is discussed on the basis of these results.

Temperature dependence of the hyperfine fields for fluorine in ferromagnetic iron, nickel and gadolinium

The temperature dependence of the magnetic hyperfine fields at the sites of F nuclei implanted into ferromagnetic Fe, Ni and Gd has been studied in the temperature range from 77 K to 670 K. A pulsed proton beam was used to observe the time-differential precession of the 5/2+ state in19F. Deviations from the bulk magnetization were found for Fe and Ni. The damping of the two observed fields in Ni was interpreted in terms of a field distribution caused by an induced radiation damage. The occupation sites for F and possible mechanisms of the anomalous temperature dependence are discussed.

The effect of lattice vibrations on the pressure dependence of the electric field gradient in cadmium metal

We determined the pressure dependence of the electric field gradientq in Cd at 150, 300, and 575 K by perturbed angular correlations on111Cd. Close to the melting point,q varies less with pressure than at low temperature, although Cd becomes more anisotropic. We attribute this to volume effects which grow with increasing lattice vibration amplitudes.

Hyperfine fields amd electronic structure of non-magnetic impurities in iron

Hyperfine fields of non-magnetic impurities in iron are calculated using the local-density formalism in an embedded cluster model. The hyperfine fields are seen to result from a delicate balance between negative exchange polarized “bound-paired” states and positive “unpaired-band” contributions. Pressure and temperature dependence and effects due to lattice relaxation are discussed.

SC-molecular/cluster calculations of the electric field gradient on 5sp-impurities (Ag-Xe) in cadmium — Volume and surface effects

The electric field gradient (EFG) on impurity atoms (Ag-Xe) in hcp Cd are calculated within the SC local density molecular/cluster approach using 27 atoms. The systematic trend and change of sign with increasing impurity charge, is well reproduced and explained by a successive population of hybridized pz and px, py orbitals. Results on the volume and c/a dependence of the EFG will also be presented, as well as on the surface EFG.

A high pressure, low temperature system for μSR studies

A high pressure, low temperature system for μSR studies is described which compresses gases like He or Ar up to 14 kbar at temperatures between 10K and room temperature. The present construction of the cell, made of hardened CuBe, limits the pressure range to 7 kbar. The sample space is approximately 4 cm3. Pressure generation up to 14 kbar is accomplished in about 15 minutes while cool-down to 10K requires about 2 hours.

Self-consistent calculation of electron density and muon hyperfine field in transition metals and their compounds

The use of finite cluster models to represent the electronic structure of solids in the framework of self-consistent local density theory is reviewed. The embedding problem is discussed, and practical variational approaches to treating crystalline potentials and wavefunction boundary conditions are presented. Hyperfine fields atμ+ sites in Fe, Ni, and Co are found to result from a delicate balance between negative contributions of deep-lying (bound, paired) states and positive contributions due to polarization of band levels near the Fermi energy. The nature of muon screening, and the potential forμ+ in Cu and Al are briefly considered. Finally, we explore the likely binding sites and bonding mechanisms forμ+ in the defect compound VOx.

Hyperfine fields at Ce in GdAl2 and DyAl2

The local fields at140Ce in the cubic intermetallic compounds GdAl2 and DyAl2 have been measured with the DPAC method. At our lowest temperatures we obtainBeff (30K)=54(2) T for GdAl2 andBeff(12.5K)=27(1) T for DyAl2 which are considerably lower than the hyperfine field of the free Ce3+ ion (183 T). The (Ce)GdAl2 field is quantitatively explained by a cubic crystal field splitting of 4f states but for DyAl2 additional effects are discussed.

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

Abstract 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 dlnBμ/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.

Pressure dependence of the muon knight shift in antimony

The pressure dependence of the muon Knight shift in antimony has been measured at 30K using polycrystalline samples and at 10K using single crystals. A considerably stronger pressure dependence is observed with the field parallel to the c-axis than perpendicular. The deduced linear parts of the isotropic and axial pressure dependence are dKiso/dP=−0.19(3)%/kbar and dKax/dP−0.24 (5)%/kbar. First principle molecular-cluster calculations show the origin, of the huge Knight shift and its pressure dependence.