μ⁺SR in magnetically ordered BCC metals: Local fields, μ⁺ sites, quantum diffusion, and strain effects

Abstract

The paper gives a critical discussion of the procedures for extracting from theμ ⁺SR signals obtainable on magnetically ordered metals information onμ ⁺ sites, on local lattice distortions induced by theμ ⁺, on the local magnetic fields felt by theμ ⁺, and on quantum diffusion. Results forα-Fe are:μ ⁺ occupy O sites, the tetragonality of the elastic double-force tensor isA−B ≈ 2eV, the dipolar magnetic field acting on theμ ⁺ isB _dip=(0.66±0.02)T. Using this informationμ ⁺ hopping rates and diffusivities in Fe are deduced and compared with diffusivities obtained for hydrogen and deuterium. From this it is concluded that hydrogen in Fe diffuses via the adiabatic mechanism. In addition, the paper contains a brief summary of the theoretical background required for taking advantage of the rather large ¦A− B¦ values expected forμ ⁺ at O sites in bcc metals in order to gain information on the effects of energy asymmetries between neighbouringμ ⁺ sites on the μ⁺ hopping rates.