Magnetic magnesium alloys have an inherent load-sensitive behavior. These alloys are manufactured by casting of magnesium alloyed with the ferromagnetic element cobalt. In this context, the magnetoelastic effect can be used in order to measure mechanical loads during the component's service by means of a harmonic analysis of eddy current signals. The utilization of magnetic magnesium as a load-sensitive material in order to measure mechanical loads in structural components has been demonstrated in previous works. Another application is the magnetic labeling of the alloy. In this context the magnetic remanence is a significant characteristic value. A data track can be written directly on the material's surface by means of an electromagnetic write head. The track may contain relevant component-specific information like serial numbers, manufacture date and expected lifetime. This information can be read out by means of a sensor utilizing the giant magnetoresistive (GMR) effect. The magnetic labeling in relation to the manufactured alloy and the cooling rate during the casting process is examined in this work. The magnetic labeling of three alloys based on magnesium, cobalt and zinc has been investigated; these are MgCo4 and MgCo4Zn2. The alloys’ mechanical as well as their magnetic properties are significantly influenced by these additional alloying elements. In order to investigate the alloys’ suitability for magnetic data storage the quality of the data tracks read out using a GMR sensor are compared depending on the alloy composition. The magnetic labeling is influenced by the microstructure regarding solidification and cooling rate. A conical casting geometry with different solidification rates in top and bottom sections was used for an examination of the relationship between the density of the magnetic phases and the quality of the magnetic labeling.