Abstract
Orthorhombic HoMnO3 is a multiferroic in which Mn antiferromagnetic order induces ferroelectricity. A second transition occurs within the multiferroic phase, in which a strong enhancement of the ferroelectric polarization occurs concomitantly to antiferromagnetic ordering of Ho 4f magnetic moments. Using the element selectivity of resonant X-ray diffraction, we study the magnetic order of the Mn 3d and Ho 4f moments. We explicitly show that the Mn magnetic order is affected by the Ho 4f magnetic ordering transition. Based on the azimuthal dependence of the (0 q 0) and (0 1-q 0) magnetic reflections, we suggest that the Ho 4f order is similar to that previously observed for Tb 4f in TbMnO3, which resembles an ac-cycloid. This is unlike the Mn order, which has already been shown to be different for the two materials. Using non-resonant diffraction, we show that the magnetically-induced ferroelectric lattice distortion is unaffected by the Ho ordering, suggesting a mechanism through which the Ho order affects polarization without affecting the lattice in the same manner as the Mn order.
Highlights
INTRODUCTIONPerovskite manganites of the o-RMnO3 family (o is short for orthorhombic, R denotes a rare-earth lanthanide or Y) have been the subject of significant attention for over a decade, owing mostly to their magnetically induced ferroelectricity (type-II multiferroic behavior), which occurs for R ions heavier (smaller) than Gd [1] (i.e., Tb-Lu and Y)
Perovskite manganites of the o-RMnO3 family (o is short for orthorhombic, R denotes a rare-earth lanthanide or Y) have been the subject of significant attention for over a decade, owing mostly to their magnetically induced ferroelectricity, which occurs for R ions heavier than Gd [1] (i.e., Tb-Lu and Y)
We show that the magnetically induced polar lattice distortion is unaffected by the Ho ordering, suggesting a mechanism through which the Ho order affects ferroelectric polarization without affecting the lattice in the same manner as the Mn order
Summary
Perovskite manganites of the o-RMnO3 family (o is short for orthorhombic, R denotes a rare-earth lanthanide or Y) have been the subject of significant attention for over a decade, owing mostly to their magnetically induced ferroelectricity (type-II multiferroic behavior), which occurs for R ions heavier (smaller) than Gd [1] (i.e., Tb-Lu and Y) All materials in this family exhibit antiferromagnetic (AF) orders of Mn moments that can be described by the same parametrized ordering wave vector Q = (0 q 1), with different values of q (using Pbnm notation). In this work we study the magnetic and structural orders of o-HoMnO3 using x-ray diffraction techniques on thick single-crystalline films. Samples were mounted on the cold head of a Janis ST-400 flow cryostat and cooled to temperatures as low as 9 K
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