Keren¶

Description¶

Keren’s generalization of the Abragam relaxation function to a longitudinal field, for fitting the time-dependent muon polarization.

The function is derived in *Phys Rev B, vol. 50, 14, 10039-42 (1994)* and is given by

$P_z(t) = A\exp\left[-\Gamma(t)t\right]$

where the relaxation rate $\Gamma(t)$ is

$\Gamma(t)t = 2\Delta^2 \frac{\left\{\left(\omega_L^2 + \nu^2\right)\nu t + \left(\omega_L^2-\nu^2\right)\left(1-e^{-\nu t}\cos(\omega_L t)\right) - 2\nu\omega_L e^{-\nu t}\sin(\omega_L t)\right\}}{\left(\omega_L^2 + \nu^2\right)^2}$

$A = P_z(0)$ is the polarization at time zero, $\nu$ is the fluctuation rate (inverse correlation time), $\Delta$ is the distribution width of the local fields and $\omega_L$ is the Larmor frequency (longitudinal field times muon gyromagnetic ratio).

Properties (fitting parameters)¶

Name	Default	Description
A	1.0	Polarization at time zero
Delta	0.2	Distribution width of local fields (MHz)
Field	50.0	Longitudinal field (Gauss)
Fluct	0.2	Hopping rate (inverse correlation time, MHz)

Categories: FitFunctions | Muon

Source¶

C++ source: Keren.cpp

C++ header: Keren.h