Giant magneto-elastic coupling in multiferroic hexagonal manganites

Abstract

The motion of atoms in a solid always responds to cooling or heating in a way that is consistent with the symmetry of the given space group of the solid to which they belong. When the atoms move, the electronic structure of the solid changes, leading to different physical properties. Therefore, the determination of where atoms are and what atoms do is a cornerstone of modern solid-state physics. However, experimental observations of atomic displacements measured as a function of temperature are very rare, because those displacements are, in almost all cases, exceedingly small. Here we show, using a combination of diffraction techniques, that the hexagonal manganites RMnO3 (where R is a rare-earth element) undergo an isostructural transition with exceptionally large atomic displacements: two orders of magnitude larger than those seen in any other magnetic material, resulting in an unusually strong magneto-elastic coupling. We follow the exact atomic displacements of all the atoms in the unit cell as a function of temperature and find consistency with theoretical predictions based on group theories. We argue that this gigantic magneto-elastic coupling in RMnO3 holds the key to the recently observed magneto-electric phenomenon in this intriguing class of materials.

Perturbed angular correlations investigations on YMnO3 multiferroic manganite

“…Since the XRD measurements have been performed at room temperature, the obtained structure is the noncentrosymmetric, which allows the appearance of ferroelectricity. Magnetic measurements show a paramagnetic-antiferromagnetic transition at T N ∼75 K, also in good agreement with the values reported in literature [13,14]. Fig.…”

“…The refinement of X-ray data show that YMnO 3 samples are single phase and crystallize in the hexagonal structure (space group P 6 3 cm) with corresponding cell parameters a=b=6.1354(1)Å and c=11.3916(3)Å in excellent agreement with the values reported in the literature [13,14]. Since the XRD measurements have been performed at room temperature, the obtained structure is the noncentrosymmetric, which allows the appearance of ferroelectricity.…”

Elastic anomalies associated with structural and magnetic phase transitions in single crystal hexagonal YMnO3

“…This becomes even more complex in a system such as YMnO 3 where magnetic structures have the propagation vector k = 0, meaning that magnetic reflections occur at the same position as nuclear reflections, causing great difficulty in the refinement of both magnetic and crystal structures [37]. Lee et al [7] observed 'giant' atomic displacements in YMnO 3 from neutron and x-ray diffraction experiments and suggested that these displacements could be responsible for coupling of the magnetic and electric order parameters. However, as remarked by Chatterji et al [37], no explanation was offered as to how correlations between structural and magnetic parameters were avoided and therefore it is difficult to accept this result.…”

“…The magnetoelastic coupling effect in YMnO 3 has been the subject of much work in recent years and a series of neutron diffraction experiments has been carried out to monitor changes in lattice parameters and atomic positions at T N [7,10,29,[35][36][37]. Monitoring of changes in atomic positions and bond lengths is difficult due to the small changes involved.…”

“…Some of the most successful examples of magnetoelectric multiferroics have come from the hexagonal rare earth manganites, RMnO 3 , and significant research has been undertaken to understand the magnetic and ferroelectric properties of these compounds (see, for example, [1][2][3][4][5][6][7][8]). Of these materials YMnO 3 , with a layered structure with Y ions placed between sheets of corner sharing MnO 5 triangular bipyramids, has been of particular interest [9][10][11][12][13][14][15][16].…”