A magnetic tunnel junction comprises a conductive first magnetic electrode comprising magnetic recording material, a conductive second magnetic electrode spaced from the first electrode and comprising magnetic reference material, and a non-magnetic tunnel insulator material between the first and second electrodes. The magnetic reference material of the second electrode comprises a synthetic antiferromagnetic construction comprising two spaced magnetic regions one of which is closer to the tunnel insulator material than is the other. The one magnetic region comprises a polarizer region comprising CoxFeyBz where “x” is from 0 to 90, “y” is from 10 to 90, and “z” is from 10 to 50. The CoxFeyBz is directly against the tunnel insulator. A non-magnetic region comprising an Os-containing material is between the two spaced magnetic regions. The other magnetic region comprises a magnetic Co-containing material. Other embodiments are disclosed.