Free layer in magnetoresistive random-access memory

A magnetoresistive random-access-memory (MRAM) comprising:

• a reference layer;
• a tunnel barrier layer above the reference layer;
• and
• a free layer above the tunnel barrier layer, wherein the free layer includes:
• a first cobalt-iron-boron (CoFeB) layer on top of the tunnel barrier layer;
• a spacer layer on top of the first CoFeB layer;
• a second CoFeB layer on top of the spacer layer;
• and
• a capping layer on top of the second CoFeB layer;
• wherein the spacer layer is an alloy of a refractory metal and iron including two layers of iron with each having a thickness between 0.5 nm and 1.0 nm and three layers of the refractory metal stacked alternately with the two layers of iron and a thickness of the layer of the refractory metal between the two layers of iron is between 0.05 nm and 0.3 nm such that it does not magnetically decouple the two layers of iron, with the iron having a concentration level ranging from 20 at. % to 80 at. % of the alloy.

A magnetic tunnel junction (MTJ) stack comprising:

• a reference layer;
• a tunnel barrier layer above the reference layer;
• and
• a free layer above the tunnel barrier layer,
• wherein the free layer includes a first cobalt-iron-boron (CoFeB) layer;
• a spacer layer of an alloy comprising a refractory metal and iron;
• a second CoFeB layer;
• and a capping layer, wherein the refractory metal is zirconium (Zr), niobium (Nb), hafnium (Hf), or rhenium (Re), and the spacer layer being sandwiched between the first and the second CoFeB layer, and
• wherein the spacer layer includes two layers of iron and three layers of the refractory metal stacked alternately with the two layers of iron, wherein each of the two outer layers of the refractory metal has a thickness between 0.1 nm and 0.4 nm to provide absorption of boron;
• each of the two layers of iron has a thickness between 0.5 nm and 1.0 nm to have magnetic power to couple with the first and the second CoFeB layer;
• and the layer of the refractory metal between the two layers of iron has a thickness between 0.05 nm and 0.3 nm to not magnetically decouple the two layers of iron.