Journal of the Korean Physical Society

, Volume 62, Issue 10, pp 1489–1494

Electronic phase separation due to magnetic polaron formation in the semimetallic ferromagnet EuB6 — A weakly-nonlinear-transport study


  • Adham Amyan
    • Institute of PhysicsGoethe-University Frankfurt
  • Pintu Das
    • Institute of PhysicsGoethe-University Frankfurt
    • Institute of PhysicsGoethe-University Frankfurt
  • Zachary Fisk
    • Department of PhysicsUniversity of California

DOI: 10.3938/jkps.62.1489

Cite this article as:
Amyan, A., Das, P., Müller, J. et al. Journal of the Korean Physical Society (2013) 62: 1489. doi:10.3938/jkps.62.1489


We report measurements of weakly nonlinear electronic transport, as measured by third-harmonic voltage generation V, in the low-carrier density semimetallic ferromagnet EuB6, which exhibits an unusual magnetic ordering with two consecutive transitions at \(T_{c_1 } \) = 15.6K and \(T_{c_2 } \) = 12.5K. In contrast to the linear resistivity, the third-harmonic voltage is sensitive to the microgeometry of the electronic system. Our measurements provide evidence for magnetically-driven electronic phase separation consistent with the picture of percolation of magnetic polarons (MP), which form highly conducting magnetically ordered clusters in a paramagnetic and less conducting background. Upon cooling in zero magnetic field through the ferromagnetic transition, the dramatic drop in the linear resistivity at the upper transition \(T_{c_1 } \) coincides with the onset of nonlinearity, and upon further cooling is followed by a pronounced peak in V at the lower transition \(T_{c_2 } \). Likewise, in the paramagnetic regime, a drop of the material’s magnetoresistance R(H) precedes a magnetic-fieldinduced peak in nonlinear transport. A striking observation is a linear temperature dependence of Vpeak. We suggest a picture where at the upper transition \(T_{c_1 } \) the coalescing MP form a conducting path giving rise to a strong decrease in the resistance. The MP formation sets in at around T* ∼ 35K below which these entities are isolated and strongly fluctuating, while growing in number. The MP then start to form links at \(T_{c_1 } \), where percolative electronic transport is observed. The MP merge and start forming a continuum at the threshold \(T_{c_2 } \). In the paramagnetic temperature regime \(T_{c_1 } \) < T < T*, MP percolation is induced by a magnetic field, and the threshold accompanied by charge carrier delocalization occurs at a single critical magnetization.


Colossal magnetoresistanceMagnetic polaronsElectronic phase separation

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© The Korean Physical Society 2013