The degree of alignment of the magnetic moments of Fe3+ ions in ultrafine maghemite particles has been studied in samples with induced magnetic texture. The textured samples were prepared by freezing ferrofluids, containing 7.5 nm maghemite particles, in a magnetic field. Mossbauer spectroscopy studies of the textured samples in large magnetic fields demonstrate that the lack of full alignment is not an effect of large magnetic anisotropy, as suggested recently, but that the effect is rather due to canting of individual spins.

The antiferroelectric (AFE) phase, in which nonpolar and polar states are switchable by an electric field, is a recent discovery in promising multiferroics of hexagonal rareearth manganites (ferrites), h-RMn(Fe)O 3 . However, this phase has so far only been observed at 60−160 K, which restricts key investigations into the microstructures and magnetoelectric behaviors. Herein, we report the successful expansion of the AFE temperature range (10−300 K) by preparing h-DyFeO 3 films through epitaxial stabilization. Room-temperature scanning transmission electron microscopy reveals that the AFE phase originates from a nanomosaic structure comprising AFE P3̅ c1 and ferroelectric P6 3 cm domains with small domain sizes of 1− 10 nm. The nanomosaic structure is stabilized by a low c/a ratio derived from the large ionic radius of Dy 3+ . Furthermore, weak ferromagnetism and magnetocapacitance behaviors are observed. Below 10 K, the film exhibits an M-shaped magnetocapacitance versus magnetic field curve, indicating unusual magnetoelectric coupling in the AFE phase.

High-quality MoFe 2 O 4 epitaxial films, exhibiting p-type conductivity and room-temperature ferrimagnetism, were successfully fabricated by a pulsed laser deposition technique. In this experiment, the MoFe 2 O 4 and MoFe 2 O 6 targets prepared via a vacuum-sealed annealing and air annealing were used. The result shows that the spinel MoFe 2 O 4 epitaxial films are obtained by using the MoFe 2 O 4 target, while films with cation-vacant spinel structures exhibiting n-type conductivity are obtained by using the MoFe 2 O 6 target even under reductive deposition conditions. Thus, controlling the oxygen content in the target is crucial to realize p-type conductivity probably related to the requirement of highly reductive Mo 3+ ions. The MoFe 2 O 4 film shows room-temperature ferrimagnetism with a large in-plane magnetic anisotropy (5 × 10 5 erg/cm 3 ) and high saturation magnetization (0.7 μ B /f.u.). In addition, the film exhibits an anomalous Hall effect and magnetoresistance at room temperature. Density functional theory calculations reveal that the p-type conductivity of MoFe 2 O 4 is derived from the holes generated in the occupied Mo 3+ 4d 3 t 2g majority spin orbitals. Article pubs.acs.org/crystal

Mn2Mo3O8 simultaneously exhibits ferroelectric polarization and unique magnetic properties, such as strong magnetoelectric coupling and magnetic-field-induced collinear-to-noncollinear spin structure transitions. However, practical applications of multiferroic Mn2Mo3O8 are hindered by low spontaneous magnetization (0.01 μ B/f.u. at 2 K) owing to the collinear spin order. Herein, we report the emergence of large spontaneous magnetization of 0.35 μ B/f.u. by applying 0.5% tensile strain to c-axis-oriented Mn2Mo3O8 epitaxial films. The Mn and Mo valence states were divalent and tetravalent, respectively. The enhanced spontaneous magnetization was directed in the in-plane direction, in contrast to that in the case of the bulk. These results suggest that the film has a noncollinear spin structure with tilted Mn2+ magnetic moments from the c-axis probably due to the tensile strain. We also performed first-principles calculations and demonstrated that the direction of the Mn2+ magnetic moment is sensitive to tensile strain.

Oxynitride MnTaO2N exhibits a helical spin order in contrast to the isostructural oxide MnTiO3 with a G-type antiferromagnetism. To understand the role of the nitride ions on the magnetism, in this study, we theoretically investigated the structural and magnetic properties of MnTaO2N. Band calculations based on the density functional theory revealed that besides the most stable anion coordinations of cis-MO4N2 octahedra (M = Mn and Ta), the other coordinations such as trans-MO4N2, MO3N3, and MO5N are also considered to coexist due to the small total energy difference. This results in random existence of the nitride ions in MnTaO2N. The magnetic properties were investigated using the Heisenberg model to quantify the coupling energy (J) between Mn 3d5 local moments. Interestingly, the average J of the Mn–N–Mn bonds (J 1N) was four times larger than that of the Mn–O–Mn bonds (J 1O), mainly due to the covalent nature of Mn–N bonds. In comparison to MnTiO3, which contains only one type of magnetic interaction, J 1O, MnTaO2N has various kinds of magnetic interactions due to the random existence of the nitride ions. In addition, the J 1O value became comparable to the next-nearest-neighbor interaction (J 2). These results caused spin frustration, which is a prerequisite to the emergence of the helical spin order in MnTaO2N.