Magnetic properties of quasi-one-dimensional Ising-chain compounds FexCo1−xNb2O6 at very low temperatures

Abstract

Combining very low-temperature experiments such as neutron diffraction, magnetometry, and specific-heat measurements, we report on the magnetic properties of the FexCo1−xNb2O6 series of compounds. This investigation demonstrates that the ground state for x = 0.2, 0.4, and 0.6, previously reported as totally frustrated, is composed of Ising-like ferromagnetic chains that are antiferromagnetically ordered. Ordering at these compositions is observed to occur below 2 K. The magnetic structure is obtained from neutron diffraction, and susceptibility measurements allow us to estimate the values of intra- and interchain exchange constants, the former being clearly dominant. Fe/Co cation disorder reduces the average exchange strength within and between chains, reflecting the tendency to suppress long-range magnetic order. The diffuse magnetic signal observed by neutron diffraction slightly above the Néel temperature is analyzed to extract information on short-range magnetic correlations. Magnetization curves at 80 mK and specific-heat measurements reveal that an external magnetic field easily breaks the antiferromagnetic order, leading to a high magnetization due to the alignment of the ferromagnetic Ising chains.