Narrow Results

The neutron diffraction and measurements of specific heat and magnetization were carried out on single crystals of a quantum spin ice system Yb₂Ti₂O₇. The thermal hysteresis loops of temperature dependence of the magnetization and neutron diffraction intensity indicate a first-order ferromagnetic transition, where the used single crystals are confirmed to have a sharp peak structure in the specific heat (C)–temperature (T) curve at T_C ∼ 0.2 K. The magnetic structure analysis of neutron diffraction results revealed that the Yb³⁺ moments have a ferromagnetic collinear structure along [001] directions with ordered moment value 1.1 ± 0.1 μ_B at 0.03 K. The mechanism of ferromagnetic transition of Yb₂Ti₂O₇ will be discussed.