Disorder-driven spin-reorientation in multiferroic h-YMn1−xFexO3

Abstract

Magnetic structure evolution of multiferroic hexagonal YMn 1-x Fe x O 3 (x= 0, 0.05, and 0.1) has been studied by carrying out detailed temperature-dependent neutron diffraction at zero and 5T fields.Thermodynamic data confirm antiferromagnetic ordering at T N in all the compositions. Our sub-T N neutron diffraction results assign the magnetic structure of pure YMnO 3 to Γ 1 irreducible representation. Over the perturbative-doping range, magnetic structure changes via Γ 1 +Γ 2 for YMn 0.95 Fe 0.05 O 3 on to Γ 2 for YMn 0.9 Fe 0.1 O 3 , as the maiden compositional analogue of spinreorientation; its occurrence in temperature-domain already reported for several manganites.Moreover, while the large thermal isostructural changes observed above T N are subdued in the ordered state, small alterations by the applied 5T-field are relatively uniform across, confirming strong magneto-elastic nature of the system. Decrease of the ordered magnetic moment (µ ord ) and planar magnetic frustration noted with Fe-doping is enhanced by the applied field; apparently through canting.Keywords: Multiferroics, Magneto-elasticity, Frustrated Antiferromagnet, Neutron Diffraction. PACS: 75.50.Ee, 75.85.+t , 61.05.fm, 75.75 2Materials that possess coexistent magnetic and electrical orderings in single phase are known as Multiferroics. 1 Hexagonal YMnO 3 is a member of their special class known as geometrically frustrated multiferroics, and is one of the most intensively studied h-RMnO 3 . 2 It undergoes ferroelectric (FE) transition at T C ~ 900K and antiferromagnetic (AFM) ordering at T N ~70K. [3][4] The crystal structure of h-YMnO 3 consists of alternating layers of MnO 5 trigonal bipyramids. These bipyramids (in trimer-combinations, sharing a common planar Oxygen) are corner-linked in the abplane to form a triangular lattice, and are separated from one another along the c-axis by the planes of Y-ions. 5 The geometric effect of buckling of the trimerized MnO5-bipyramids is accompanied by the inversion-symmetry-breaking displacements of Y-layers, originating the ferroelectric polarization. 6 Regarding the magnetic structure, below T N the Mn 3+ moments order in the a-b plane, and form a 2D non-collinear spin structure, characterized by an angle of 120 o between the neighbouring spins. [7][8][9] Consequent to the 2D magnetism and triangular lattice, the magnetic structure of YMnO 3 is frustrated, characterized by the frustration factor f = |Θ CW |/T N , found to be as large as 7.8 for YMnO 3 . 10 Here, Θ CW is the (negative) intercept on the temperature-axis of the (interpolated) high-temperature T-linear (Curie-Weiss) inverse susceptibility of the independent-spins. The antiferromagnetic (AFM) order is governed by the in-plane Mn-O-Mn super-exchange interaction, whereas the Mn-O-O-Mn supersuper-exchange interaction between the stacked triangular planes is about two order of magnitude weaker. This weak inter-layer (z=0 and z=1/2), 4,7,11 configuration is the one that differentiates among the several magnetic structures proposed f...

Spin-lattice coupling and frustrated magnetism in Fe-doped hexagonal LuMnO 3

“…It was noted in the work by Solovyev et al, [14] using first-principles methods that the different magnetic ground state models for hYMnO 3 and hLuMnO 3 have close-by energies. In doped compounds of hYMnO 3 and hLuMnO 3 , refinement using combination of different representations have been used to get a better result [24,25]. In Fig 3 (a) (b) and (c), the refined atomic positions, x of Mn/Fe and z of Lu1 and Lu2 are plotted as a function of temperature.…”

Effect of atmosphere annealing on the magnetic and dielectric properties of YMn0.8Fe0.2O3 multiferroic ceramics

“…However, single phase multiferroic materials are quite rare in nature, and hexagonal YMnO 3 in space group of P6 3 cm is one of the most intensively studied materials [5][6][7]. The structure of the hexagonal YMnO 3 can be described as corner-linked MnO 5 trigonal bipyramids separated by a layer of Y 3? ions.…”