Magnetic phase diagram of magnetoelectric ${\text{CuFeO}}_2$ in high magnetic fields

A series of ultrasonic velocity measurements using both high-field pulsed and conventional superconducting magnets were used to determine the magnetic phase diagram of magnetoelectric ${\text{CuFeO}}_2$ up to 53 T. The results clearly indicate a previously undetected transition at about 49 T below 10 K. Analysis of Landau-type free energy suggests that this new phase boundary is due to a spin-flop transition.

Figure 1

(Color online) Temperature dependence of the normalized velocity variation of longitudinal waves propagating along $c$ $\left(\Delta V/V_{Lz}\right)$ and $x$ axis $\left(\Delta V/V_{Lx}\right)$. Curves in black/red correspond to increasing/decreasing temperature sweeps.

Figure 2

(Color online) Field dependence of the normalized velocity variation of longitudinal waves propagating along the $x$ axis $\left(V_{Lx}\right)$ and $c$ axis $\left(V_{Lz}\right)$. The continuous blue curves represent data collected using a quasistatic field produced by a conventional superconducting magnet up to 10 T.

Figure 3

(Color online) Field dependence of the normalized velocity variation of longitudinal waves propagating along the $x$ axis. For clarity, results obtained below and above $T_{N2}\sim 10.6\text{K}$ are presented separately.

Figure 4

(Color online) Field dependence of the normalized velocity variation of longitudinal waves propagating along the $c$ axis. For clarity, results obtained below and above $T_{N2}\sim 10.6\text{K}$ are presented separately.

Figure 5

(Color online) Magnetic phase diagram of ${\text{CuFeO}}_2$. The lines are guides for the eyes, while the boundary for the critical field $H_{N1}$ (red curve) is obtained by fitting the experimental data point using a mean field prediction. The arrows represent the proposed spin configurations. The broken line represents results from Landau theory.

Figure 6

Field dependence $\left(H/J_1\right)$ of the magnetization $M_z$ calculated at 0 K for the (3,1) commensurate state.