Abstract:
Neutron diffraction has been used to investigate the critical behavior at the onset of antiferromagnetic phase transitions in a (111) oriented Pt₇₃Fe₂₇ film grown on an α-axis oriented sapphire (α-Al₂O₃) substrate. As in the bulk, there is an antiferromagnetic reorientation transition from the Q₁=2π/α(1∕2,1/2, 0) phase to the Q₂=2π∕α(1∕2,0,0) phase upon cooling. The temperature dependence of the integrated intensity of the (1∕2,1∕2,0) and the (1∕2,0,0) antiferromagnetic Bragg peaks yielded the Néeel temperature of 160.25±0.2 K and a reorientation transition temperature of 95±0.2 K. The magnetization critical exponent β is found to be 0.368±0.013 for the Q₁ phase and 0.37±0.02 for the Q₂ phase. These critical exponents are in excellent agreement with the predictions of the 3d Heisenberg universality class. A comparison of the transition temperatures and the exponents in the film and in single crystal at the same alloy composition is presented.
