Crystal structure, magnetic and dielectric behavior of h-LuMn x O 3 7 δ ceramics (0.95 r x r 1.04) A. Baghizadeh a,n , J.M Vieira a , J.S. Amaral b , M.P. Graça c , M.R. Soares d , D.A. Mota e , V.S. Amaral b a Department of Materials & Ceramic Engineering & CICECO, Aveiro University, 3810-193 Aveiro, Portugal b Physics Department & CICECO, Aveiro University, Aveiro, Portugal c Department of Physics and I3N, Universidade de Aveiro, 3810-193 Aveiro, Portugal d LCA- Central Analytical Laboratory & CICECO, Aveiro University, Aveiro, Portugal e IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia da Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal article info Article history: Received 26 March 2015 Received in revised form 4 July 2015 Accepted 25 July 2015 Available online 30 July 2015 Keywords: Multiferroic Hexagonal LuMnO 3 Vacancy Magnetoelectric coupling abstract Lattice constants, magnetic properties and dielectric behavior of h-LuMn x O 3 7δ solid solution (0.95 rx r1.04) of bulk ceramic samples prepared by the solid state reaction method were studied to determine the role of stoichiometry changes on the crystalline structure and magneto-electric coupling. It is found that increasing of Mn content results in reduction of cell volume of h-LuMn x O 3 7δ ceramics mostly due to shrinkage of a-axis length. The antiferromagnetic interactions of Mn 3 þ ions weaken with cell volume contraction. A weak ferromagnetic contribution appeared in all samples and extends up to the Neel temperature, T N . Irreversibility in temperature dependent magnetic measurements already reported for stoichiometric compositions of hexagonal RMnO 3 oxides appears for all h-LuMn x O 3 7δ samples right below Neel ordering transition. An increase of magnetic coercive field and magnetization on cooling below T N in samples is observed in field dependent magnetization and rises as x increases. In addition to the antiferromagnetic ordering transition at T N , two anomalies of the temperature dependent magnetic susceptibility and dielectric constant are identified below T N , centered at 69 K and 31 K re- spectively, being probably due to inhomogeneity of the crystalline structure inside ceramic grains. Changes of the dielectric constant at T N can be attributed to magneto-electric coupling in the off-stoi- chiometric hexagonal LuMn x O 3 7δ lattice. The behavior of the dielectric relaxation follows a thermally activated mechanism with activation energy values characteristic of polaron hoping. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Multiferroic hexagonal RMnO 3 7δ (R ¼ Ho-Lu, Y, Sc) materials have been investigated because they show both magnetoelectric coupling and magneto-elastic coupling, presenting open chal- lenges to the understanding of underlying physics behind coupling of ferroic properties [1–4]. In the effort to explain and ascertain the interdependence of each ferroic property on the observed physical and chemical properties of these materials, authors have mainly dealt with A-site or B-site doping approaches [2,5–8] or by changing synthesis conditions [9–13]. Although, upon doping or changing synthesis conditions, one is able to change the ferroic properties, still from all these experimental adjustments and theoretical approaches the role of rare-earth and metal ions on unit cell parameters and magnetic and dielectric properties could not be clearly and explicitly figured out. It was found in perovskite materials like LaMnO 3 7δ that creating off-stoichiometric A-site or B-site compositions would be a suitable tool for exploring the role of rare-earth (A-site) and transition metal ions (B-site) and of their effect upon the change in properties [13–18]. However, such concept has been seldom used to set the role of R and Mn ions in hexagonal rare-earth manganites [19–22]. Since Lu does not have localized 4f 14 electrons, it does not carry free magnetic moment to participate in magnetic interactions in h-LuMnO 3 7δ lattice and hence Mn 3 þ ions are the sole magnetic ions inside the structure. The AFM ordering is explained by the 2D magnetic interaction of frustrated Mn 3 þ ions forming trimmers of nearest neighbor Mn 3 þ ions in the triangular network of basal plane of the hexagonal lattice of the RMnO 3 compounds [2]. Any change in Mn or Lu will duly modify magnetic moment (interaction), dielectric polariza- tion behavior and the magneto-electric coupling. The Lu-depen- dent or Mn-dependent properties may reveal additional details of Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials http://dx.doi.org/10.1016/j.jmmm.2015.07.082 0304-8853/& 2015 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: ali.baghizhadeh@ua.pt (A. Baghizadeh). Journal of Magnetism and Magnetic Materials 395 (2015) 303–311