Crystal structure and magnetic properties of the unique Jahn-Teller system 154Sm0.6Sr0.4MnO3 -: art. no. 094432

Structural neutron diffraction investigations as well as data on resistance, linear susceptibility, and second harmonic of magnetization are presented for (Sm0.6Sr0.4MnO3)-Sm-154 manganite. The structural studies reveal the unique Jahn-Teller (JT) character of this compound which is established to exhibit a Pbmn space group. Unusual large coherent JT distortions are found to develop below T(JT)approximate to 180 K and remain even in a metallic ferromagnetic phase below the Curie point T(c)approximate to 120 K. In the paramagnetic region the resistance is consistent with polaron hopping. A field hysteresis of the second harmonic is observed above T-c. This evidences the existence of the macroscopic ferromagnetic regions in the paramagnetic matrix. In contrast, temperature dependence of the linear susceptibility reveals a plateau at T>T-c. These conflicting peculiarities of the magnetic properties can be explained by assuming the ferromagnetic behavior to be associated with the antiferromagnetic regions possessing a weak ferromagnetism. The ordered regions appear as a result of first order transition at T approximate to 160 K, destroy at T-* approximate to 137.5 K and reveal a characteristic three-critical behavior for T -->T-*+0. Change in a balance between the ferromagnetic double exchange hopping of e(g) electrons and the antiferromagnetic interactions of t(2g) spins, which caused by the cooperative JT effect, and the charge ordering correlations are supposed to account for the anomalous magnetic behavior above T-c.