The Mn-doping effect on the charge ordering state of La1/3Sr2/3FeO3

The longitudinal ultrasonic velocity (Vl), as well as resistivity has been measured in single-phase polycrystalline La1/3Sr2/3Fe1−xMnxO3 (x = 0, 0.025, 0.05) at a frequency of 10 MHz, from 20 K to 300 K. It is found that with increasing Mn-doping level, the resistivity increases and the charge ordering transition temperature TCO shifts to lower temperature. For all samples, upon cooling down from 300 K, a substantial softening in Vl above TCO and dramatic stiffening below TCO are observed. This abnormal elastic softening above TCO can be described well by the mean-field theory, which indicates that this feature is due to the electron–phonon coupling via the Jahn–Teller effect and this coupling is enhanced with the Mn doping. Below TCO, another softening in Vl is observed for x = 0, and weakens with the increasing of Mn content. This character is attributed to the breathing-type distortion of Fe–O octahedron and suggests that the charge disproportionation (CD) transition is suppressed by the Mn substitution.

Research highlights▶ For La1/3Sr2/3Fe1−xMnxO3 system, with increasing the Mn-doping level, the resistivity increases and the charge ordering transition temperature TCO shifts to lower temperature. ▶ Two kinds of lattice distortion exist in La1/3Sr2/3Fe1−xMnxO3 samples. ▶ The first is the distortion arising from the Jahn–Teller effect of high-spin Fe4+, and the second is the breathing-type distortion. ▶ With the Mn doping, the Jahn–Teller effect is enhanced, and the breathing-type distortion is weakened.