  We have studied the relationship between the structure and the spin Hall
angle of the early 5d transition metals in X/CoFeB/MgO (X=Hf, Ta, W, Re)
heterostructures. Spin Hall magnetoresistance (SMR) is used to characterize the
spin Hall angle of the heavy metals. Transmission electron microscopy images
show that all underlayers are amorphous-like when their thicknesses are small,
however, crystalline phases emerge as the thickness is increased for certain
elements. We find that the heavy metal layer thickness dependence of the SMR
reflects these changes in structure. The spin Hall angle largest
|\theta$_{SH}$| of Hf, Ta, W and Re (~0.11, 0.10, 0.23 and 0.07, respectively)
is found when the dominant phase is amorphous-like. We find that the
amorphous-like phase not only possesses large resistivity but also exhibits
sizeable spin Hall conductivity, which both contribute to the emergence of the
large spin Hall angle.
