Circularly polarized soft x-ray diffraction study of helical magnetism in hexaferrite

Abstract

Magnetic spiral structures can exhibit ferroelectric moments as recently demonstrated in various multiferroic materials. In such cases the helicity of the magnetic spiral is directly correlated with the direction of the ferroelectric moment and measurement of the helicity of magnetic structures is of current interest. Soft x-ray resonant diffraction is particularly advantageous because it combines element selectivity with a large magnetic cross-section. We calculate the polarization dependence of the resonant magnetic x-ray cross-section ͑electric dipole transition͒ for the basal plane magnetic spiral in hexaferrite Ba 0.8 Sr 1.2 Zn 2 Fe 12 O 22 and deduce its domain population using circular polarized incident radiation. We demonstrate there is a direct correlation between the diffracted radiation and the helicity of the magnetic spiral.Magnetic spiral structures can exhibit ferroelectric moments as recently demonstrated in various multiferroic materials. [1][2][3][4] In such cases the helicity of the magnetic spiral is directly correlated with the direction of the ferroelectric moment and measurement of the helicity of magnetic structures is of current interest. Magnetic spiral structures have been observed directly with neutron diffraction ͑ND͒ and resonant x-ray diffraction ͑RXD͒ 5 as their superstructure gives rise to satellite reflections. With polarized neutron diffraction the chirality of the magnetic structure can be determined, as was first predicted by Blume 6 and achieved by Siratori. 7 Recently this has been particularly insightful for the study of ferroelectric magnetic spiral structures in TbMnO 3 , 8 LiCu 2 O 2 , 9 and CuFe 1−x Al x O 2 10 observing that the chirality of the magnetic structure is manipulated with applied electric field. With circular polarized nonresonant x-ray diffraction the chiral magnetic domain population in holmium has been determined 11 and, very recently, polarization analysis has been used to study the cycloidal magnetic domains in multiferroic TbMnO 3 in its ferroelectric phase. 12 An advantage of RXD is that via tuning the incident energy to a particular absorption edge, element specific magnetism is observed. In the case of transition metals, the L 2,3 edge is particularly insightful because the core electron is excited from the core 2p to the 3d valence states and the ͑empty͒ magnetic states are directly probed. The magnetic cross-section is significant compared to the charge crosssection and soft x-ray resonant diffraction has emerged as a very valuable technique with which to study magnetic and orbital order in transition-metal oxides, in particular to distinguish between charge, orbital, and magnetic order. [13][14][15][16] Correlation between the RXD intensity and the helicity of the magnetic spiral has been demonstrated by imaging of the spiral domains in holmium 17 but a quantitative analysis of the diffracted intensities is missing.In this Brief Report we calculate the polarization dependence of the RXD cross-section and deduce the domain population of the magn...

The effect of field cooling on a spin-chiral domain structure in a magnetoelectric helimagnet Ba0.5Sr1.5Zn2Fe12O22

“…The discovery ignited a renewed interest in the hexaferrite systems which have long been used for magnetic technologies [12], and triggered off extensive studies on magnetoelectric properties [13] in various types of helimagnetic hexaferrites such as Y-type Ba 2 Mg 2 Fe 12 O 22 [14,15], M-type Ba(Fe,Sc,Mg) 12 O 19 [16], Z-type Sr 3 Co 2 Fe 24 O 41 [17], and U-type Sr 4 Co 2 Fe 36 O 60 [18]. Furthermore, the long size of the c axis in these helimagnetic hexaferrites provides a benefit to studying their magnetic structures by means of the resonant X-ray diffraction with longwavelength soft X-rays at the energy of the Fe L 3 edge [8,19,20]. In this study, we examine the effect of magnetic-and/or electric-fieldcooling on the spin-chiral domains in Ba 0.5 Sr 1.5 Zn 2 Fe 12 O 22 by means of the scanning resonant X-ray microdiffraction technique using a circularly polarized and highly focused soft X-ray beam.…”

Cycloidal Order of4fMoments as a Probe of Chiral Domains inDyMnO3

“…The resonant case was worked out in detail for a magnetic spiral [28], which is analogous to the present cycloid. The measurement of circular dichroism connected to the ferroelectric polarization in DyMnO 3 requires sizeable domains of welldefined P. These were obtained by a novel approach that uses the local charging of the sample by the x-ray beam.…”

Origin of the anomalous low-temperature phase transition in BaVS3

“…Resonant soft XRD is able to directly measure and disentangle charge, orbital, and magnetic ordering contributions in such a 3d 1 system by directly accessing the 3d states responsible for physical properties. 13,14 To clarify the origin of the T X transition observed in BaVS 3 we have studied the associated SL reflection and determined its q position. We have also determined the temperature, energy, and polarization dependence of the SL reflections observed at V L 2,3 edges.…”