Antiferromagnetically Spin Polarized Oxygen Observed in MagnetoelectricTbMn2O5

Abstract

We report the direct measurement of antiferromagnetic spin polarization at the oxygen sites in the multiferroic TbMn2O5, through resonant soft x-ray magnetic scattering. This supports recent theoretical models suggesting that the oxygen spin polarization is key to the magnetoelectric coupling mechanism. The spin polarization is observed through a resonantly enhanced diffraction signal at the oxygen K edge at the commensurate antiferromagnetic wavevector. Using the fdmnes code we have accurately reproduced the experimental data. We have established that the resonance arises through the spin polarization on the oxygen sites hybridized with the square based pyramid Mn 3+ions. Furthermore we have discovered that the position of the Mn 3+ ion directly influences the oxygen spin polarization.PACS numbers: 75.30. Gw, 78.70.Ck, 75.50.Ee, 75.47.Lx The ability to couple magnetism and ferroelectricity, namely the control of charges by changing the magnetic state of a material, paves the way to the development of novel multifunctional devices. Recently, the goal of being able to control the ferroelectric state by the application of a magnetic field was realized in TbMnO 3 [1], and launched a new area of research into magnetoelectric multiferroic perovskite materials. In these materials the coupling is provided through complex non-linear magnetic structures. Central to current theories[2, 3] seeking to explain the spontaneous electric polarization in perovskite manganites, is the presence of a magnetic cycloid, arising from magnetic frustration. Such a magnetic structure breaks global inversion symmetry and allows the development of a ferroelectric moment. It is interesting therefore, that in TbMn 2 O 5 , a material found to have a huge magnetoelectric coupling [4], larger even than that in TbMnO 3 , the magnetic structure was found to be almost collinear [5]. This suggests that an entirely different mechanism drives the multiferroic behavior in TbMn 2 O 5 , opening up a new route for the development of multiferroic devices. A possible mechanism has been determined by Moskvin and coworkers [6,7], who show the importance of the charge transfer between the manganese and oxygen, and the resulting spin polarization of the oxygen sites.In this letter we report the direct observation of a long range, correlated spin polarization at the oxygen sites in TbMn 2 O 5 , observed using resonant soft x-ray scattering at the oxygen K edge. This resonance is seen at the (0.5,0,0.25) antiferromagnetic wavevector corresponding to the magnetic order. Through ab-initio calculations of the incident x-ray energy dependence of the diffraction intensity we show that the ordered spin polarization arises from the oxygen sites hybridized with the Mn 3+ ions. The temperature dependence of the oxygen spin polarization and the manganese ordering, confirms that the oxygen spin polarization appears at the antiferromagnetic transition, simultaneous to the onset of the ferroelectric dipole moment. We suggest that the oxygen spin polarization is a key fact...

Paramagnetic collective electronic mode and low temperature hybrid modes in the far infrared dynamics of orthorhombic NdMnO3

“…Our reflectivities show at about 120 K slightly higher than T N , the collective band sharpens by a temperature driven mechanism in which Mn moments develop magnetic long-range order assisting electron correlation and localization. This band profile change might also point to spin polarization hybridization with Mn 3+ ions at the oxygen sites as has been reported for TbMn 2 O 5 [42].…”

Magnetic structure and electric field effects in multiferroic YMn2O5

“…Recently, it has been shown that the induced magnetic moments at the oxygen might be important to understand the multiferroicity in these materials. 21,24 Resonant x-ray diffraction is an elemental sensitive technique that can probe the magnetism of the different elements separately, but information on the different ions is still missing. Another important aspect to understand multiferroics is the interplay between electric fields and the magnetic order, as this represents the magnetoelectric coupling directly.…”

“…21 Here we have checked for such spin polarization in both Y and Er compounds (RMn 2 O 5 , R=Y,Er) by measuring the commensurate magnetic reflection ( fig. 4.…”

“…7,[17][18][19][20][21][22][23] The soft x-ray range has the advantage to directly probe the 3d Mn and 4f R states using the L 2,3 and the M 4,5 edge resonances, respectively. Such technique has been previously used to study the Er 7,18 and Tb 20-22 compounds of the RMn 2 O 5 series.…”

The contribution of Diamond Light Source to the study of strongly correlated electron systems and complex magnetic structures

“…Nevertheless, significant insights have been obtained using RSXD [44][45][46], and RSXD is also an area of active interest for Diamond theorists [47][48][49][50]. A good example is provided by the so-called hexaferrites.…”