Field-induced incommensurate spin structure of TbNiAl4

TbNiAl${}_{4}$ exhibits incommensurate and commensurate magnetic ordering as a function of temperature. As a function of applied field it undergoes a series of magnetic phase transitions. The first of these transitions, into an intermediate spin arrangement, is the source of a large inverse magnetocaloric effect, an unusual result given that an aligning field is being applied. This has potential uses in magnetic cooling. Here, single-crystal neutron diffraction with applied magnetic field is used to obtain the intermediate field spin arrangement in TbNiAl${}_{4}$. We find that not only does the applied field drive the system from commensurate to incommensurate ordering, but that the phase transition shows hysteresis such that a mixed state simultaneously showing commensurate and incommensurate antiferromagnetic ordering, along with ferromagnetism, can be obtained.