With the increasing size of the memory system inside today's chips, memories are becoming a critical part of the design of modern embedded systems. SRAM, DRAM and FLASH, respectively used for cache, working memory and non-volatile storage, are the three main memory technologies of current memory hierarchies. But all are facing to manufacturing constraints in the most advanced node, which compromises further evolution. Magnetic RAM (MRAM) technology is a very attractive alternative offering simultaneously reasonable performance and power consumption efficiency, high density and non-volatility. Among the MRAM technologies, while Toggle MRAM suffers from scalability issue and Spin Transfer Torque MRAM (STT-MRAM) is facing to data retention failure, Thermally Assisted Switching MRAM (TAS-MRAM) uses a scheme allowing a fully scalable bit cell, low power writing and excellent data retention. This paper demonstrates how features of TAS-MRAM can lead to power efficient memory systems. A case study of a TAS-MRAM-based L2 cache shows significant power saving while keeping reasonable performance.