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SUMMARY:Studies of $\\mu^+$ Diffusion and Trapping in dilute Fe Alloys by 
 Longitudinal  $\\mu^+$ Spin Relaxation Technique
DTSTART;VALUE=DATE-TIME:20220830T164000Z
DTEND;VALUE=DATE-TIME:20220830T170000Z
DTSTAMP;VALUE=DATE-TIME:20220826T121024Z
UID:indico-contribution-3810@indico.stfc.ac.uk
DESCRIPTION:Speakers: Nobuhiko Nishida (JAEA & Tokyo Tech.)\nIn the late 1
 970s and 1980s $\\mu^+$spin rotation experiments were performed elaboratel
 y to study $\\mu^+$ diffusion and trapping in Fe and Fe alloys. In Fe allo
 ys not many experiments were performed\, probably because the unavoidable 
 inhomogeneity of the magnetization in ferromagnetic Fe alloys bring about 
 the fast dephasing of spin rotation and may obscure the diffusion and trap
 ping effects. Recently at J-PARC MUSE we have found that the measurement o
 f the longitudinal $\\mu^+$spin relaxation time $T_L$ in ferromagnetic Fe 
 alloys is the effective new microscopic technique to study the $\\mu^+$ di
 ffusion and trapping in Fe dilute alloys and to investigate how the hydrog
 en interacts with the principal alloying elements in an attractive or repu
 lsive manner and how the local lattice strain induced by them affect the h
 ydrogen diffusion. We revisit the $\\mu^+$SR studies of diffusion and trap
 ping in Fe alloys. We have measured the temperature dependence of the $T_L
 $ in several dilute Fe alloys containing principal alloying elements such 
 as Ni\, Mn\, Cr\, Ti\, Al\, Si and interstitial impurities C and O.  In so
 me alloys the temperature dependence of $1/T_L$ exhibits the peaks and in 
 some other alloys a hump in a broad temperature region.  We have developed
  the `two-state' model of ferromagnetic dilute Fe alloys: the trapped stat
 e by impurity atom and the freely diffusing state of $\\mu^+$. The $\\mu^+
 $SR results are well explained by this model. The peaks are due to the mot
 ional narrowing effect where the $\\mu^+$-impurity interaction is repulsiv
 e and the $\\mu^+$ diffuse in the crystal apart from the impurity atoms. T
 he broad hump is due to the trapping and de-trapping of $\\mu^+$ by impuri
 ties. The 1st principle calculations of hydrogen-impurity interactions\, t
 he magnetic moment of the impurity and the local strain induced by the imp
 urity in dilute Fe alloys are compared with the $\\mu^+$SR results.\n\nhtt
 ps://indico.stfc.ac.uk/event/53/contributions/3810/
LOCATION:Science and Technology Campus\, University of Parma
URL:https://indico.stfc.ac.uk/event/53/contributions/3810/
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