Aqueous mixtures of 1,2-dimyristoyl-sn-glycero-3phosphocholine (DMPC), 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine diethylenetriamine pentaacetate (DMPE DTPA) with complexed thulium ions (Tm3+), and cholesterol with varying molar ratio were studied at different temperatures in the presence and absence of a magnetic field. For mixtures without cholesterol weakly magnetically alignable small disks, so-called bicelles, are formed at temperatures below the phase transition temperature (5 22 C), as shown by cryo-transmission electron microscopy (cryo" TEM) and small-angle neutron scattering (SANS). In presence of 16 mol % cholesterol the disk size and the magnetic alignability were larger within the entire temperature range studied (5-40 C). Cholesterol acts as a spacer between DMPE DTPA with complexed Tm3+, allowing these molecules to integrate more frequently into the planar part of the bicelles. Replacing DMPC partially by cholesterol thus lead to an increase in magnetic aligning by a higher amount of the magnetic handles (Tm3+ complexed to DMPE-DTPA) in the plane and by an increased number of phospholipids in the enlarged bicelles. The magnetic aligning was most pronounced at 5 C. The temperature-dependent structural changes of the DMPC/cholesterol/DMPE DTPA/Tm3* aqueous mixtures are complex, including the transient appearance of holes in the disks at intermediate temperatures.