The crystal magnetic field in a proton-polarized lanthanum magnesium nitrate single crystal

Abstract

Knowledge of the crystal magnetic fieldH _c is necessary for proton polarization measurements in polarized targets by the internal field method [1, 2]. Because of the importance of lanthanum magnesium nitrate (LMN) single crystals for low-energy polarized proton targets [3],H _c has been calculated for LMN on the basis of new x-ray diffraction data. We find thatH _c=ApP₂(cosθ), wherep is the proton polarization andP ₂ the second Legendre polynomial depending onθ, the angle between crystalc-axis and external magnetic field, andA is a constant characteristic for LMN. Our result$A = - \left( {0.242 \pm \begin{array}{*{20}c} {0.028} \\ {0.090} \\ \end{array} } \right) Oe$ leads to a field only about half as large as expected according to previous assumptions. The difference is due to the markedly different proton positions, revealed by the x-ray structure analysis.