Antiferromagnetic phase transitions in an orderedPt3Fe(111)film studied by neutron diffraction

Abstract

Neutron diffraction has been used to investigate the critical behavior at the onset of antiferromagnetic phase transitions in a (111) oriented ${\mathrm{Pt}}_{73}{\mathrm{Fe}}_{27}$ film grown on an $a$-axis oriented sapphire $(\ensuremath{\alpha}\text{\penalty1000-\hskip0pt}{\mathrm{Al}}_{2}{\mathrm{O}}_{3})$ substrate. As in the bulk, there is an antiferromagnetic reorientation transition from the ${Q}_{1}=2\ensuremath{\pi}∕a(1∕2,1∕2,0)$ phase to the ${Q}_{2}=2\ensuremath{\pi}∕a(1∕2,0,0)$ 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 N\'eeel temperature of $160.25\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and a reorientation transition temperature of $95\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The magnetization critical exponent $\ensuremath{\beta}$ is found to be $0.368\ifmmode\pm\else\textpm\fi{}0.013$ for the ${Q}_{1}$ phase and $0.37\ifmmode\pm\else\textpm\fi{}0.02$ for the ${Q}_{2}$ 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.