Magnetic Structure of Iron Manganite by Neutron Diffraction

Abstract

Pure iron manganite FeMn2O4 was prepared at 1250°C and quenched. It crystallizes in the b.c. tetragonal system D4h19. Neutron diffraction measurements above the Curie temperature (120°C) show that the inversion parameter is 0.91 (nearly inverse spinel). The spontaneous magnetization at 4.2°K measured in high static and pulsed fields is 1.55 μB/mol. The magnetic moment was observed to increase linearly above 70 kOe and showed the presence of a strong anisotropy with easy axis near the [101] direction (unusual fact). Neutron diffraction measurements at 4.2°K lead to the determination of the magnetic structure of FeMn2O4. The tetrahedral sublattice moments (4.3 μB) are collinear in a (010) plane making an angle of − 172° with Ox [100]. Spins in octahedral sites (3.1 μB) are divided into four magnetic sublattices with a pyramidal arrangement whose axis of symmetry lies in the plane (010) and makes an angle of 14° with Ox [100]. At 55°K the spins of the octahedral sublattices become collinear, the easy magnetization direction remaining unchanged up to 310°K where it changes to the [110] direction, the magnetic structure of FeMn2O4 becoming completely collinear.

Structural and magnetic transitions in spinel FeMn2O4 single crystals

“…A typical single crystal boule obtained from the floating-zone furnace is shown in the inset of Figure 1 [22], which is comparable with the previous reports [15,20].…”

“…Instead, we note the sharp raise of M below ~ 400 K, and an obvious decrease below 50 K. For the easy determination of the transition temperatures, we calculate dM/dT as shown in Figure 2(b). Note that there are two peaks with one at T FI-1 ~ 373 K and the other at T FI-2 ~ 50 K. The transition temperatures are comparable to those previously reported [11,15]. In a previous neutron diffraction study, the authors reported a ferrimagnetic ordering below 390 K followed by sublattice spin reorientations below 55 K resulting in a non-collinear ordering [15].…”

“…The tetragonal structure is manifested due to a cooperative Jahn-Teller (JT) distortion of the MnO 6 octahedra [12][13][14]. Magnetically, this system orders in a ferrimagnetic (FI) configuration [15,16]. While there is a trend that the transition temperature T FI decreases with increasing x [17], most of these studies have been on the iron-rich region i.e.…”

First-principles study of the inversion thermodynamics and electronic structure ofFeM2X4(thio)spinels (M=Cr, Mn, Co, Ni;Santos‐Carballal1, Roldan2, Grau‐Crespo3 et al. 2015Phys. Rev. B

“…The upper limit (x = 0.3) of the shallow inversion free energy that we predicted agrees semiquantitatively with the experimental inversion degree (x = 0.5) found for FeMn 2 O 4 in a conductivity and thermopower 35 investigation, as well as inferred from the study of a series of spinels, 36 see Table III. The inversion degree has also been found in neutron diffraction experiments to be at x = 0.91 37,38 which is in reasonably good agreement with the global minimum calculated here. We speculate that the two inversion degrees of FeMn 2 O 4 may be hampered by kinetic control, a situation that is outside the scope of this paper, but which explains the different cation arrangements described in the literature.…”

“…~ 0.0 33 0.00 FeMn2O4 0.5 35,36 0.10 and 1.00 0.91 37,38 FeMn2S4* ----0.03 FeMn 2 X 4 . At 1000 K, the scenario for FeMn 2 O 4 is unique in this study, as in addition to the global minimum of ΔF config at x = 1, it has a local one at x = 0.1.…”