Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

We studied the high-field phase diagram of a chiral-lattice antiferromagnet Sr(TiO)Cu₄PO₄)₄ by means of ultrasound, dielectric, and magnetocaloric-effect measurements. These experimental techniques reveal two new phase transitions at high fields, which have not been resolved by previous magnetization experiments. Specifically, the c₆₆ acoustic mode shows drastic changes with hysteresis for magnetic fields applied along the c axis, indicating a strong magnetoelastic coupling. Combined with cluster mean-field theory, we discuss the origin of these phase transitions. By considering the chiral-twist effect of Cu₄O₁₂ cupola units, which is inherent to the chiral crystal structure, the phase diagram is reasonably reproduced. The agreement between experiment and theory suggests that this material is a unique quasi-two-dimensional spin system with competing exchange interactions and chirality, leading to a rich phase diagram.