Enhanced magnetopiezoelectric effect at the Néel temperature in CaMn2Bi2

Abstract

We have experimentally studied a magnetopiezoelectric effect (MPE), i.e. dynamic distortion caused by ac electric currents, in the antiferromagnetic conductor CaMn 2 Bi 2 at low temperatures down to 77 K using laser Doppler vibrometry. When ac electric currents are applied to CaMn 2 Bi 2 , dynamic displacement signals which increase in proportion to the current amplitude are clearly observed at 77 K, but their magnitude and temperature dependence strongly depend on Joule heating effects caused by the applied electric currents. Especially, poor thermal contact of CaMn 2 Bi 2 samples to the sample holder produces second-harmonic displacement signals owing to thermal expansion due to the Joule heating, and tends to affect the temperature dependence of the MPE signals. In a measurement run without any heating effects, a sharp enhancement of the MPE signal is observed at the Néel temperature of CaMn 2 Bi 2 , which suggests that fluctuations of itinerant Mn moments near the Néel temperature play an important role in the MPE. We speculate that electric currents produce nonequilibrium antiferromagnetic moments via the antiferromagnetic Edelstein effect and the induced antiferromagnetic momemts enhance the MPE signal with the help of a large magneto-volume coupling near the Néel temperature. The MPE efficiency as a piezoelectric response reaches 300-500 pC/N at a maximum, which is comparable to high values of piezoelectric coefficients detected in the piezoelectric (ferroelectric) ceramics.

Large Magneto-piezoelectric Effect in EuMnBi2 Single Crystal at Low Temperatures

“…The numerical integration of velocity data with respect to time corresponds to division of velocity by frequency in the frequency domain, and thus the calculated displacement diverges almost in proportion to 1/f (f: frequency) at low www.nature.com/scientificreports www.nature.com/scientificreports/ frequencies. Similar frequency dependence of background signals in the MPE measurements was observed at 77 K in previous papers 9,10 . In the following sections, background levels at the electric-current frequency are estimated by fitting the spectra with A/f + B (A and B: fitting parameters).…”

“…2c, and also it can be subject to stiffness of the bonding material between the sample and the Cu sample holder. We have used GE varnish to avoid Joule heating effects during the MPE measurements 10 , and the deformation of the backside face of the EuMnBi 2 sample may affect the detected magnitudes of the MPE signal.…”

“…Here, we kept the frequency and the amplitude of the AC electric current at 10 kHz and 100 mA, respectively. As mentioned in our previous papers 9,10 , stable measurement of the temperature dependence of small MPE signals is difficult in our experimental set-up, since the laser position and focus inevitably change at different temperatures owing to thermal expansion of the sample and the holder at high temperatures. www.nature.com/scientificreports www.nature.com/scientificreports/ Nevertheless, the temperature dependence data should be important to clarify the physical mechanism of the MPE, and thus it is discussed in detail by conducting two measurement runs.…”

“…The magneto-piezoelectric effect (MPE), which was very recently explored theoretically 7,8 and experimentally 9,10 , provides a new mechanism of piezoelectric responses in low-symmetry magnetic metals. While the usual piezoelectric effect is allowed in noncentrosymmetric insulators and semiconductors, the MPE occurs in noncentrosymmetric metals possessing many conduction electrons.…”

Superconductivity induced by fluctuations of momentum-based multipoles

“…Although the magnetic octupole is an EM multipole, the OM multipole order with broken inversion symmetry and TRS has recently been attracting significant attention. For example, Fulde-Ferrell-Larkin-Ovchinnikov superconductivity coexisting with the magnetic quadrupole [18,19], magnetoelectric effect [10][11][12][23][24][25] and magnetopiezoelectric effect [23,118,119] originating from the odd-parity magnetic multipole have been suggested. More than 110 OM multipole materials have been identified by a recent group-theoretical study [23].…”