Uniaxial stress-induced symmetry breaking for muon sites in Fe

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Abstract
Uniaxial stress has been used on Fe single crystals to induce muon-precession frequency shifts. The frequency shift for a nominally pure Fe sample at 302 K was -0.34±0.023 MHz per 100 microstrain (με) along the 〈100〉 magnetization axis. This corresponds to a change of magnetic field at the muon of 25.1±1.6 G/100 με. For an Fe (3 wt. % Si) single crystal, the shifts were -0.348±0.008 MHz/100 με (25.7±0.5 G/100 με at 300 K), and -0.279±0.010 MHz/100 με (20.6±0.7 G/100 με at 360 K). The agreement between the shifts for Fe and Fe (3 wt. % Si) shows the effect to be intrinsic to iron and not strongly impurity sensitive. These shifts and their temperature dependence (1/T) are dominated by the effect of strain-induced population shifts between crystallographically equivalent, but magnetically inequivalent sites. Their magnitudes are in good agreement with theoretical predictions by Jena, Manninen, Niemenin, and Puska and by extrapolation from calculations on Nb and V by Sugimoto and Fukai, especially if both 4T(0) and 1T sites con- tribute comparably.