Colossal magnetoresistance in low-doped EuTi1− x Nb x O3 ( x  = 0.003 and 0.005)

We studied the magnetization (M), magnetostriction (λ||), resistivity (ρ), magnetoresistance (MR), and thermoelectric properties of low-doped EuTi1−xNbxO3 (x = 0.003 and 0.005). In both the samples, Eu2+(4f7) spins order antiferromagnetically at TN≅5.5K, and the paramagnetic to antiferromagnetic transition is accompanied by a spontaneous contraction of the length in the absence of magnetic field and a positive magnetostriction under external magnetic fields. ρ(T) shows non-metallic behavior in the temperature range 400–2.5 K but a weak kink at TN in a zero magnetic field. The application of an external magnetic field induces the semimetal-metal transition and negative MR. The magnitude of negative MR has a maximum value of 82% (57%) under 7 T for x = 0.003 (0.005) at T = 2.5 K, and the MR monotonously decreases with increasing temperature. Thermopower data indicate that the doped carriers are electrons. It is suggested that scattering of 4d1 electrons doped in the impurity band by 4f spin fluctuations is responsible for the colossal magnetoresistance.