The layered perovskites RCr(BO3)2 (R = Y and Ho) with magnetic triangular lattices were studied by performing ac/dc susceptibility, specific heat, elastic and inelastic neutron scattering, and dielectric constant measurements. The results show (i) both samples' Cr 3+ spins order in a canted antiferromagnetic structure with TN around 8-9 K, while the Ho 3+ ions do not order down to T = 1.5 K in HoCr(BO3)2; (ii) when a critical magnetic field HC around 2-3 T is applied below TN , the Cr 3+ spins in the Y-compound and both the Cr 3+ and Ho 3+ spins in the Ho-compound order in a ferromagnetic state; (iii) both samples exhibit dielectric constant anomalies around the transition temperature and critical field, but the Ho-compound displays a much stronger magnetodielectric response. We speculate that this is due to the magnetostriction which depends on both of the Cr 3+ and the Ho 3+ ions' ordering in the Ho-compound. Moreover, by using linear spin wave theory to simulate the inelastic neutron scattering data, we estimated the Y-compound's intralayer and interlayer exchange strengths as ferromagnetic J1 =-0.12 meV and antiferromagnetic J2 = 0.014 meV, respectively. The competition between different kinds of superexchange interactions results in the ferromagnetic intralayer interaction.

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.

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View the article online for updates and enhancements. Related contentMagnetic structure in iron borates RFe3(BO3)4 (R = Er, Pr): a neutron diffraction andmagnetization study C Ritter, A Vorotynov, A Pankrats et al. Abstract. Neutron diffraction measurements were performed on the iron borate DyFe 3 (BO 3 ) 4 to investigate details of the crystallographic structure, the low temperature magnetic structure and its magnetic properties. DyFe 3 (BO 3 ) 4 adopts at room temperature the P3 1 21 symmetry and becomes antiferromagnetic below T N = 39 K. Both, the rare earth and the iron sublattice, follow the same magnetic propagation vector = [0, 0, ½] which leads to a doubling of the crystallographic unit cell in the c-direction. The easy axis anisotropy of the rare earth determines the moment orientation to be mainly along c. No spin reorientation is found between T N and 1.5 K, however, a small anomaly in the thermal dependence of the unit cell aparameter is found at about 27 K which could be connected to repopulation of low lying Kramers doublets of Dy 3+. The magnetic moment value of the Fe-moment is at 1.5 K with Fe = 4.5 B only slightly smaller than expected for an S = 5/2 ion while the Dy moment is strongly reduced and amounts only to Dy = 6.4 B .

Temperature dependent neutron diffraction studies were performed on SmFe(3)(BO(3))(4). The crystallographic structure was determined to stay as R32 over the whole studied temperature range of 2 K < T < 300 K. A magnetic phase transition characterized by the magnetic propagation vector κ = [0 0 3/2] takes place at T(N) = 34 K. The magnetic structure sees an easy-plane arrangement within the trigonal basal a-b-plane of ferromagnetic layers of iron and samarium having a canting angle of about 70° relative to each other. Neighbouring layers in the c-direction are antiferromagnetically coupled; at 2 K the magnetic moment values amount to μ(Fe ) = 4.2(1) μ(B ) and μ(Sm) = 0.8(2) μ(B). The non-Brillouin type increase of the iron magnetic moment below T(N) points to a strong Fe-Sm exchange and to the simultaneous appearance of long range magnetic order on both sublattices.

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