Direct control of magnetic chirality in NdMn2O5 by external electric field

Abstract

Detailed investigation of the incommensurate magnetic ordering in a single crystal of multiferroic NdMn2O5 has been performed using both non-polarized and polarized neutron diffraction techniques. Below TN ≈ 30.5 K magnetic Bragg reflections corresponding to the nonchiral type magnetic structure with propagation vector k1 = (0.5 0 kz1) occurs. Below about 27 K a new distorted magnetic modulation with a similar vector kz2 occurs, which is attributed to the magnetization of the Nd 3+ ions by the Mn-sub-lattice. Strong temperature hysteresis in the occurrence of the incommensurate magnetic phases in NdMn2O5 was observed depending on the cooling or heating history of the sample. Below about 20 K the magnetic structure became of a chiral type. From spherical neutron polarimetry measurements, the resulting low-temperature magnetic structure kz3 was approximated by the general elliptic helix. The parameters of the magnetic helix-like ellipticity and helical plane orientation in regard to the crystal structure were determined. A reorientation of the helix occurs at an intermediate temperature between 4 K and 18 K. A difference between the population of right-and left-handed chiral domains of about 0.2 was observed in the as-grown crystal when cooling without an external electric field. The magnetic chiral ratio can be changed by the application of an external electric field of a few kV/cm, revealing strong magnetoelectric coupling. A linear dependence of the magnetic chirality on the applied electric field in NdMn2O5 was found. The results are discussed within the frame of the antisymmetric super-exchange model for Dzyaloshinsky-Moria interaction.I.

Optical and magnetic investigation of multiferroic and magnetocaloric properties of Nd0.8Tb0.2Mn2O5

“…The reported XRD patterns allow us only to calculate the c-lattice constants. However, previous crystallographic studies carried out on our samples [16,19,24] have identified an orthorhombic structure with the Pbam space-group symmetry. The reported lattice constants a, b, and c are found to be 7.4940, 8.6071, and 5.6934 Å for NdMn 2 O 5 (at 300 K); 7.531(5), 8.610(5), and 5.719(5) Å for Nd 0.8 Tb 0.2 Mn 2 O 5 (at 3.8 K); and 7.351, 8.60, and 5.690 Å for TbMn 2 O 5 (at 300 K), respectively.…”

“…Furthermore, its electrical polarization develops at T 2 ∼ 26 ± 2 K (T C ), arises only in an incommensurate state, being in contrast with other RMn 2 O 5 multiferroic members [11]. These properties render NdMn 2 O 5 unique as a reference member of the RMn 2 O 5 series to provide a deeper understanding of the fundamental mechanisms behind its magnetic and electric properties [15][16][17][18]. Doping this parent compound with smaller rare-earth elements, such as terbium (Tb), could enhance its multiferroic character.…”