We conducted small-angle neutron scattering (SANS) experiments on the ferromagnetic semimetal ${\mathrm{EuB}}_6$, where we observed first-hand evidence for the presence of magnetic polarons. We carried out SANS experiments over a large range of scattering vectors $|\vec{\mathbf{q}}|$, ranging from 0.006 to 0.140 ${\AA }^{-1}$ , and temperatures of 2 to 60 K. Just above $T_{\mathrm{C}}$ our experiments show magnetic scattering intensity, which has a Lorentzian dependence on the wave vector, characteristic of the presence of magnetic polarons. Below $T_{\mathrm{C}}$ the polarons merge, and most of the observed intensity is due to scattering from domains. We were able to extract a correlation length $\xi$ that ranges from 100 to 300 Å for the size of the magnetic polarons. This size is much larger than one would expect for magnetic fluctuations of a three-dimensional Heisenberg ferromagnet, demonstrating the influence of magnetic polarons on the phase transition.

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• Colossal magnetoresistance
• Critical exponents
• Electrical conductivity
• Ferromagnetism
• Magnetic interactions
• Magnetic order
• Magnetic texture
• Metal-insulator transition
• Phase separation
• Spin dynamics
• Spintronics
• Small angle neutron scattering