Crystal structure and magnetic properties of the unique Jahn-Teller system(Sm0.6Sr0.4MnO3)-Sm-154 - 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 u nique Jahn-Teller (JT) character of this compound which is established to e xhibit 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 fe rromagnetic phase below the Curie point T(c)approximate to 120 K. In the pa ramagnetic region the resistance is consistent with polaron hopping. A fiel d hysteresis of the second harmonic is observed above T-c. This evidences t he existence of the macroscopic ferromagnetic regions in the paramagnetic m atrix. In contrast, temperature dependence of the linear susceptibility rev eals a plateau at T>T-c. These conflicting peculiarities of the magnetic pr operties can be explained by assuming the ferromagnetic behavior to be asso ciated with the antiferromagnetic regions possessing a weak ferromagnetism. The ordered regions appear as a result of first order transition at T appr oximate to 160 K, destroy at T-* approximate to 137.5 K and reveal a charac teristic three-critical behavior for T -->T-*+0. Change in a balance betwee n the ferromagnetic double exchange hopping of e(g) electrons and the antif erromagnetic interactions of t(2g) spins, which caused by the cooperative J T effect, and the charge ordering correlations are supposed to account for the anomalous magnetic behavior above T-c.