Structural, magnetic and dielectric properties of Ni doped LiInCr4O8 breathing pyrochlore

Abstract

Herein, polycrystalline compounds of breathing pyrochlore LiInCr4-xNixO8 (x = 0, 0.1, 0.2, 0.4) were synthesized by the solid state method. Structure, magnetism, and dielectric properties have been investigated with x-ray diffraction, Raman spectroscopy, magnetic susceptibility, isothermal magnetization, AC impedance, and heat capacity measurements. The mean particle size of the Ni substituted samples decreased from 1.95 μm to 1.22 μm, which is larger than the size determined by the Scherrer formula and the Williamson-Hall method. Raman scattering revealed slightly red-shifted modes Eg, F2g(2), F2g(3), and A1g, which were caused by higher effective atomic mass and increased bond strength. At low temperatures, field cooled and zero field cooled susceptibility measurements, as well as frequency dependent χac data, show a spin-glass type freezing. The resulting Mydosh parameter p of x = 0.4 is 0.01, suggesting the spin glass state. Magnetic measurements exhibit a large negative CW temperature (|θCW| > 290 K), initially decreasing and then increasing at high Ni concentration, in support of the relationship between magnetic interactions and the structural parameters of Cr–Cr spins. Despite the large negative θCW in substituted samples, long-range magnetic order was suppressed at high Ni contents. With increasing nickel concentration, the spin gap gradually vanished, indicating a significant reduction in breathing distortion. The isothermal magnetization at 2 K confirms antiferromagnetic characteristics and weak ferromagnetic components in the substituted samples. When the frequency is increased at room temperature, the dielectric data shows a drop in dielectric constant as well as lower dielectric loss. At low frequencies, interfacial polarization mechanisms play a crucial role. In contrast, at high frequencies, the dielectric constant becomes frequency independent up to ∼ 105 Hz, due to reverse electron motion. The low temperature specific heat behavior implies the good insulator characteristic of LiInCr3.6Ni0.4O8 and a residual entropy feature related to spin-glass type freezing.