Dipolar effects on the critical fluctuations in Fe: Investigation by MIEZE

Abstract

Iron is one of the archetypical ferromagnets to study the critical fluctuations at a continuous phase transition thus serving as a model system for the application of scaling theory. We report a comprehensive study of the critical dynamics at the transition from the ferro- to the paramagnetic phase in Fe, employing the high-resolution neutron spin echo technique MIEZE. The results show that the dipolar interactions lead to an additional damping of the critical spin fluctuations at small momentum transfers $\mathbf{q}$. The results agree essentially with scaling theory if the dipolar interactions are taken into account by means of the mode-coupling equations. However, in contrast to expectations, the dipolar wavenumber $q_D$ that plays a central role in the scaling function $f(\kappa /q,q_D/\kappa )$ becomes temperature dependent. In the limit of small $\mathbf{q}$ the critical exponent $z$ crosses over from 2.5 to 2.0.

6 pages, 6 figures

References in corpus (3)

• Fluctuation-induced first-order phase transition in Dzyaloshinskii-Moriya helimagnets
• Critical spin-flip scattering at the helimagnetic transition of MnSi
• Neutron spin echo spectroscopy under 17T magnetic field at RESEDA

Cited by in corpus (4)

• Using small-angle scattering to guide functional magnetic nanoparticle design
• MIEZE Neutron Spin-Echo Spectroscopy of Strongly Correlated Electron Systems
• On the resolution of a MIEZE spectrometer
• Paramagnetic fluctuations of the magnetocaloric compound MnFe${}_4$Si${}_3$