Hole concentration induced transformation of the magnetic and orbital structure in Nd{1-x}Sr{x}MnO{3}

TL;DR

This study investigates how hole concentration affects magnetic and orbital structures in Nd{1-x}Sr{x}MnO{3}, revealing systematic phase transitions and orbital orderings through neutron diffraction analysis.

Contribution

It provides detailed insights into the relationship between hole doping, orbital ordering, and magnetic phases in Nd{1-x}Sr{x}MnO{3}, highlighting the coexistence of charge and magnetic orders.

Findings

Identification of phase transitions with increasing x.

Observation of orbital orderings linked to MnO6 octahedral distortions.

Detection of charge ordering near x=3/4 or 4/5.

Abstract

In order to study the magnetic and crystal structures in the Nd{1-x}Sr{x}MnO{3} system, we have peformed neutron diffraction measurements on melt-grown polycrystalline samples with 0.49 < x < 0.75. As a function of hole concentration x, the system shows systematic transformation of magnetic and crystal structures, which is consistently explained by the change of the character of Mn eg orbitals. With increasing x, the Nd{1-x}Sr{x}MnO{3} system exhibits a metallic ferromagnetic state, a metallic A-type AFM state, and then an insulating C-type AFM state. The CE-type charge-ordered AFM state was observed only in the vicinity of x=1/2, and it coexists with the A-type AFM state for x > 1/2, indicating that the energy difference between these two states is extremely small. We also found that the MnO{6} octahedra are apically compressed in the CE-type and A-type AFM states due to the d(3x2-r2)/d(3y2-r2) or d(x2-y2) orbital orderings, respectively, whereas they are apically elongated by the rod-type d(3z2-r2) orbital ordering in the C-type AFM state. In addition, a selective broadening of Bragg peaks was observed in the C-type AFM phase, and its x dependence strongly suggests the charge ordering for a commsurate value of the hole concentration at either x=3/4 or x=4/5.