In this article, manufacture of a magnetic magnesium alloy based on the known magnesium alloys AZ91 or ZEK200 together with samarium–cobalt is investigated. The objective of the investigations is to produce an Mg alloy by die casting, possessing both magnetic characteristics and satisfactory mechanical properties with the aim of obtaining an Mg alloy which can be utilized as a lightweight sensor material. Inverse magnetostriction (Villari Effect) is exploited in order to verify the instantaneous operating forces in lightweight structural components made from Mg such as a vehicle's stub axle. The magnetic properties subject to cyclic loading are determined with the aid of a harmonic analyze of eddy current signals. Results show that for an MgSmCoZn alloy, an unambiguous linear dependency exists between the applied mechanical loading and the harmonic's measured values. The mechanical properties of the MgSmCoZn cast alloy have a similar order of magnitude as those of Mg alloys employed in engineering, such as for example AZ91, and thus possess a good standard.