Tracking the continuous spin-flop transition inNi3TeO6by infrared spectroscopy

Abstract

Easy axis antiferromagnets usually exhibit a first order spin-flop transition when the magnetic field is applied along the easy axis. Recently a colossal magnetoelectric effect was discovered in Ni3TeO6, suggesting a continuous spin-flop transition across a narrow phase in this material [Y. S. Oh, et al., Nature Comm. 5, 3201 (2014)]. Additional evidence is, however, desirable to verify this mechanism. Here we measure the infrared vibrational properties of Ni3TeO6 in high magnetic fields and demonstrate that the phonon anomalies are consistent with a second-order mechanism.

Magnetoelectric Coupling through the Spin Flop Transition inNi3TeO6

“…2(a)), we immediately notice that while the intensities of the 1.2 eV peaks are similar, there is a large anisotropy between 1.5 and 2.2 eV, with the absorption being much stronger along c (≈2500 cm −1 ) than in the ab plane (≈1300 cm −1 ). Temperature effects are also more interesting in this direction, with the 4.2 K data showing (i) an overall hardening of the excitations, (ii) an intensity increase near 1.9 eV, and (iii) fine structure on the leading edge of the 1.1 eV band that may correspond to phonon side bands [16]. Examination of the 1.9 eV excitation reveals that the peak shape is a strong function of temperature.…”

“…Recent magnetization and magneto-infrared experiments do in fact reveal the possibility of an unexplored transition between 30 and 35 T as well as metamagnetic transitions at 52 and 70 T for B c [15,16].…”

“…Moreover, Ni 3 TeO 6 sports the largest linear magnetoelectric coupling constant in a single-phase material known to date (α = 1, 300 ps/m) [13]. Metamagnetic transitions accompanied by extraordinarily large polarization changes have been discovered at 52 and 70 T [15], and indications of an unexplored transition between 30 and 35 T were observed as well [16]. The colossal polarization, rich magnetic phase diagram, and large spin-orbit coupling due to incorporation of the Te centers raise the possibility of large dynamic magnetoelectric coupling in this system.…”

Magnetoelectric excitations in multiferroic Ni3TeO6

“…As predicted by the factor group analysis for the crystal structure with R3 symmetry, 10,11 9 E(x,y,x 2 -y 2 ,xy,xz,yz) and 9 A(x 2 +y 2 ,z 2 ,z) modes are expected, both IR and Raman active. 15 All 18 modes can be seen in the IR spectra up to 300 K.…”

“…6 The previous report of a ferroelectric phase transition at 1000 K 13 is questionable, because the reported dielectric dispersion is typical of the MaxwellWagner relaxation in conducting systems, 14 and no switchable ferroelectric polarization has been observed above 53 K. Lattice dynamics of Ni 3 TeO 6 were investigated above 150 cm -1 using infrared (IR) spectroscopy as a function of temperature and magnetic field. 15 Phonon anomalies due to spin-phonon coupling were observed near T N and a spin-flop transition close to 9 T, but also near 30 T, which suggest another magnetic phase transition at 30 T. 15 In addition, interlocked chiral and polar domain walls were observed at room temperature, unveiling a complex coupling between the chiral and polar order parameters. 16 Due to sum rules, the static magnetoelectric coupling should be governed by magnetoelectric excitations (electromagnons) in the GHz and/or THz regions.…”