Scientists at Rice University have determined that cerium magnesium hexalluminate, previously thought to host a quantum spin liquid, actually exhibits a novel state of matter driven by competing magnetic forces. The discovery, detailed in a study published in Science Advances, explains the material's lack of magnetic order and continuum of energy states through neutron scattering experiments. Researchers describe it as the first observation of such a phenomenon.
Cerium magnesium hexalluminate (CeMgAl11O19) drew attention for mimicking signs of a quantum spin liquid, including no magnetic ordering and a spread of low-energy states. However, a team co-led by Rice University's Pengcheng Dai found these traits stem from a delicate balance between ferromagnetic and anti-ferromagnetic interactions rather than quantum fluctuations. The material allows magnetic ions to adopt mixed arrangements, creating degenerate states that produce similar observational data to a true quantum spin liquid but without ongoing transitions between states once settled near absolute zero. Neutron scattering and other measurements revealed the unusually weak boundary between these magnetic behaviors, enabling freer movement among configurations. Bin Gao, a co-first author and research scientist at Rice, noted, 'The material had been classified as a quantum spin liquid due to two properties: observation of a continuum of states and lack of magnetic ordering. But closer observation showed that the underlying cause wasn't a quantum spin liquid phase.' Tong Chen, another co-first author at Rice, added, 'It was not a quantum spin liquid, yet we were observing what we thought were quantum spin liquid-associated behaviors.' Dai, the corresponding author, called it 'a new state of matter that, to our knowledge, we are the first to describe,' emphasizing the need for careful data scrutiny in quantum research. The findings were supported by the U.S. Department of Energy and other foundations.
