Magnetic Structure and Magnetotransport Properties of La_0.7Sr_0.3Mn_{1 – x}Ni _x O₃

Abstract

La_0.7Sr_0.3Mn_{1 – x}Ni _x O₃ (0.12 ≤ x ≤ 0.35) compositions have been studied using neutron diffraction, magnetometry, and measurements of magnetotransport properties. At temperatures of 5–300 K, these compounds were found to have a rhombohedral crystal structure. The substitution of nickel for manganese has been shown to result in a decrease in the Curie temperature from 278 K (х = 0.12) to 60 K (х = 0.3); in this case, the spontaneous magnetization of the compositions decreases to zero (x = 0.33). The magnetoresistive effect for the semimetals with 0.12 ≤ x < 0.18 increases near the Curie temperature, whereas the magnetoresistance of semiconducting compositions with х ≥ 0.2 progressively decreases as the temperature increases. For compositions with х ≥ 0.25, an antiferromagnetic G-type component has been found by neutron diffraction, the Neel temperature of which reaches 260 K (at х = 0.35). The study of the La_1–ySr _y Mn_0.65Ni_0.35O₃ (y ≤ 0.3) system showed that the content of ferromagnetic component decreases with increasing Sr content. It has been inferred that the antiferromagnetism of the compositions with х > 0.25 is due to the strong negative exchange interactions Ni²⁺–О–Ni²⁺ and Mn⁴⁺–О–Mn⁴⁺ and the absence of ionic order. The obtained data have been used to construct the magnetic phase diagram of the La_0.7Sr_0.3Mn_1–xNi _x O₃ (0.12 ≤ x ≤ 0.35) system.