Anomalous thermal expansion and magnetostriction of single crystal Tb.27Dy.73Fe2

Single crystal magnetostriction and thermal expansion measurements are reported on Tb.27Dy.73Fe2. A spin reorientation at T = 283K causes the sudden onset of a very large magnetostrictive distortion which yields a huge anomalous contribution to the linear thermal expansion. The temperature and magnitude of this contribution is field controlled. The expansion coefficient can be varied from +5 to +115×10^-6/°K. Normal magnetostrictive behavior is observed above 283K. Below this temperature a change in the easy axis from the highly magnetostrictive [111] axis to the weakly magnetostrictive [100] direction causes an anomalous field dependence. Here large external fields are required to saturate the moment along [111].