Magnetic Structure of EuTiO3

Abstract

Europium titanate has the cubic perovskite structure containing divalent Eu (7 μB) and tetravalent Ti. From magnetic measurements we find that EuTiO3 is one of the few antiferromagnetic materials with a positive θ (TN=5.3°K, θ=3.8°K). At 1.3°K the magnetic moment (σ) increases linearly with field to 10 kOe; above 14 kOe the moment saturates and σ=156 emu/gm (6.93 μB) at 20 kOe. Powder neutron-diffraction work indicates that EuTiO3 has the Type G magnetic structure in which a given Eu++ has six nearest-neighbor europium ions antiparallel and 12 next-nearest-neighbor europium ions parallel. In a perovskite structure where only the 12-coordinated ion is magnetic, i.e., Eu++, the molecular field relations for a two sublattice model yield J1/k=−0.021°K, where J1 is the effective intersublattice exchange interaction, and J2/k=0.040°K, where J2 is the effective intrasublattice exchange interaction. The signs of J1 and J2 are opposite to those found in the europium chalcogenide series. The chalcogenides, however, have the rocksalt structure in which the number of 90° cation-anion-cation interactions differs from the perovskite structure.

EuTiO3magnetic structure studied by neutron powder diffraction and resonant x-ray scattering

“…The value of the Eu ++ magnetic moment (μ = 7 ± 1 μ B ) was found to be consistent to the free ion as previously reported. 15 The large uncertainty arises from the large neutron cross section of the Eu ions, which severely affects the observed intensities.…”

“…Specific heat measurements suggest a structural instability at T A = 282 K, 14 while high resolution x-ray powder diffraction is able to resolve a peak splitting due to the cubic to tetragonal transition only at T B = 235 K. 13 In order to reconcile this discrepancy Allieta et al propose the presence of short-range correlation in the transient regime between T A and T B , a position supported by results from their pair distribution function analysis below T A . 13 At T N = 5.3 K the localized 4f moments on the Eu ++ (S = 7/2, L = 0) sites order in a G-type antiferromagnetic arrangement, 15 that is, the six nearest neighbors have opposite spins while the 12 next-nearest neighbors have parallel spins. Concomitant with the onset of antiferromagnetism, the dielectric constant decreases abruptly (∼3.5%) and shows a strong enhancement as a function of the applied magnetic field (∼7% at B ∼ 1.5 T), providing evidence for magnetoelectric coupling.…”

Nonlinear pressure dependence ofTNin almost multiferroic EuTiO3

“…At T N = 5.5 K the compound undergoes a paramagnetic to antiferromagnetic (AFM) phase transition [4]. Over a large temperature regime a transverse optic long wave length mode softens reminiscent of a ferroelectric phase transition [2,3].…”

Electric field modulation of the tetragonal domain orientation revealed in the magnetic ground state of quantum paraelectric EuTiO3

“…Although EuTiO 3 has been known as a G-type antiferromagnet (AF) below T N ∼ 5.5 K since the 1960s 5 , its magnetoelectric properties were only revealed in 2001 by a 7% drop in the dielectric constant at T N 6 . Early efforts to model EuTiO 3 shared one critical feature: an assumption of cubic crystal symmetry throughout the phase diagram [7][8][9] .…”