Neutron diffraction and ESR studies of pseudocubic Nd0.77Ba0.23MnO3 and its anomalous critical behavior above TC

Neutron diffraction, magnetization, and ESR studies of pseudocubicNd0.75Ba0.25MnO3and its critical behavior aboveTCRyzhov1, Lazuta2, Smirnov3 et al. 2005Phys. Rev. B190130View full textAdd to dashboardCite

“…The OO ′ transition is not usually accompanied by the octahedral tilting. In this case c/ √ 2 ≈ a ≈ b above T JT and c/ √ 2 < a, b below it, as it is found in LaSr [20], LaCa [21] and x = 0.23 NdBa [14] manganites. The T −variations of the lattice parameters and unit-cell volume (Fig.2a,b) are observed above T C .…”

“…Fig.2 displays the T −variations of structural parameters. The orthorhombic distortions are small in range of the measurements as in the x = 0.23 manganite [14]. However, there are essential differences in their character.…”

“…In contrast, the data on nonlinear response of the second order clearly indicated the occurrence of an anomalous critical behavior for T C < T < T * that suggested the coexistence of the two magnetic phases. Although the x = 0.23 compound exhibited an orbital ordering due to the JT effect below T JT ∼ 350K, the neutron diffraction study did not reveal a two phase structure in the anomalous T −range [14] that would be a natural explanation of the phase separated (PS) magnetic state. In addition, according to the ESR measurements, the transition did not become hysteretic in temperature and clearly first order.…”

“…Although our measurements of the dMn-O are not a very high accuracy, they contradict the coexistence of the O and O ′ phase with the comparable volume fractions even at 220 K, and support formation of the nearly structural uniform phase below 230 K. The T −evolution of the structural parameters does not reveal any peculiarities in the anomalous T −range (T * ≈ 4 143 K ÷ 129 K ≈ T C ) which can be directly associated with the appearance of a two-phase structural state. Note that a character of the JT distortions in the x = 0.23 manganite below 150 K (dMn-O21 -dMn-O1 ≈ dMn-O1 -dMnO22), where it depends weakly on temperature [14], differs from that of the x = 0.25 manganite. Thus, the FI state and the anomalous critical behavior can occur at the different types of these distortions.…”

“…The neutron diffraction investigations have been also performed to elucidate the effects of the lattice distortions and orbital ordering. The study of the critical magnetic properties of the x = 0.23 (T C ≈ 124 K) and x = 0.25 (T C ≈ 129 K) manganites revealed a more complicated scenario than that expected for the 3D isotropic ferromagnets [12,13,14,15]. The conventional critical behavior was observed to proceed for T * < T < 2T C where T * ≈ 147 K (x = 0.23) and T * ≈ 143 K (x = 0.25).…”