Magnetic structure in iron borates RFe₃(BO₃)₄(R = Er, Pr): a neutron diffraction and magnetization study

Abstract

Neutron diffraction, susceptibility and magnetization measurements (for R = Er only) were performed on iron borates RFe(3)(BO(3))(4) (R = Pr, Er) to investigate details of the crystallographic structure, the low temperature magnetic structures and transitions and to study the role of the rare earth anisotropy. PrFe(3)(BO(3))(4), which crystallizes in the spacegroup R32, becomes antiferromagnetic at T(N) = 32 K, with τ = [0 0 3/2], while ErFe(3)(BO(3))(4), which keeps the P3(1)21 symmetry over the whole studied temperature range 1.5 K < T < 520 K, becomes antiferromagnetic below T(N) = 40 K, with τ = [0 0 1/2]. Both magnetic propagation vectors lead to a doubling of the crystallographic unit cell in the c-direction. Due to the strong polarization of the Fe-sublattice, the magnetic ordering of the rare earth sublattices appears simultaneously at T(N). The moment directions are determined by the rare earth anisotropy: easy-axis along c for PrFe(3)(BO(3))(4) and easy-plane a-b for ErFe(3)(BO(3))(4). There are no spin reorientations present in either of the two compounds but there is the appearance below 10 K of a minority phase in the Er-compound adopting a 120° arrangement of the Er-moments.

Magnetic structure of iron borate DyFe3(BO3)4: A neutron diffraction study

“…Table 2 lists the basis vectors of this IR and the refined values of their coefficients, the crystallographic details of the refinement are included in table 1. The magnetic structure found (figure 3) resembles strongly those found for TbFe 3 (BO 3 ) 4 [7] and PrFe 3 (BO 3 ) 4 [8] with a dominant easy axis orientation of the magnetic moments. The coefficients of the basis vectors describing an easy plane orientation of the two iron sites are zero or very close to (Table 2).…”

“…All magnetic peaks appear at positions not corresponding to nuclear Bragg peaks and can be indexed using the magnetic propagation vector = [0, 0, ½]. The same propagation vector has been already found in all other RFe 3 (BO 3 ) 4 compounds studied with neutrons [7][8][9][10]. It leads to a doubling of the magnetic unit cell in c-direction and is determined by the antiferromagnetic coupling between neighboring Fe spins along the helicoidal chain.…”

“…The presence of two magnetic sublattices, a structure which sees helicoidal Fe-Fe-chains with a strong one-dimensional character and the absence of direct R-O-Rinteractions [6] opens the way for a variety of magnetic ordering phenomena where the temperature dependent competition between the anisotropy of the rare earth sublattice and that of the iron sublattice leads to different magnetic structures and may induce spin reorientations and metamagnetic behavior. Previous neutron diffraction studies have established an easy-axis orientation of the magnetic moments for R = Tb, Pr [7,8] over the whole temperature range below T N and for R = Ho [9] below the spin reorientation temperature while for R = Nd, Er, Ho (above 5 K) and Y an easyplane orientation has been found [10,8,9]. Magnetic resonance data indicate for R = Gd a spin reorientation from easy-plane to easy-axis on lowering the temperature [11].…”

Ho and Fe magnetic ordering in multiferroic HoFe3(BO3)4

“…2,3 However, recent observations of improper ferroelectricity, 4,5 anomalous even within the realm of magnetoelectricity, require an even better understanding of the subject. Rare earth iron borates RFe 3 (BO 3 ) 4 , where R = rare earth, [6][7][8][9] are multiferroics, characterized by long-range magnetic wave vectors q c*, [10][11][12][13][14][15] and show a large magnetoelectric effect ( P ∼ 100 μC m −2 ). The RFe 3 (BO 3 ) 4 crystal structure 16,17 allows a dominant Fe-Fe exchange interaction, which is reflected by a T N in a narrow temperature range (30-40 K) for compounds with different R. The rare earth exchange interaction takes place via O and B, i.e., R-O-B-O-R.…”

“…To understand the magnetic structure of these compounds neutron powder diffraction on R = Y, Pr, Nd, Tb, Ho, and Er, [12][13][14][15] resonant magnetic x-ray scattering on R = Gd, 11 and nonresonant magnetic x-ray scattering on R = Nd, Gd, Tb, and Y 10 have been performed. From neutron powder diffraction it has not been possible to determine the spin direction in the basal plane, since these compounds have a trigonal crystal structure.…”