Description: anisotropic peak broadening

We based this expression for anisotropic peak broadening caused by antiphase boundaries on work by Her, Stephens et al (Acta Cryst. B 63 561 (2007)). We found it useful for fitting magnetic Bragg peaks in layered materials with much shorter magnetic correlation lengths along c than in the ab plane (Phys. Rev. B 89 100402(R) (2014); Phys Rev. B, in press).

Expression for constant wavelength data:

    lor_fwhm = C_star*((L^2)^0.5)*D_spacing  Lam / (Pi*xi_z Cos(Th)) Rad;
    prm xi_z  47.53024`_3.31957 min 0 max 1000

Expression for time-of-flight data:

    lor_fwhm = C_star*((L^2)^0.5)*D_spacing * difc_n58 * (D_spacing^2) / (Pi*xi_z ) ; 
    prm xi_z  86.31282`_1.33195 min 0 max 1000	

where xi_z is the correlation length along z.

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