Weak ferromagnetism in hexagonal orthoferrites RFeO3 (R = Lu, Er-Tb)

Abstract

Hexagonal orthoferrites of rare earths RFeO3 (R = Lu, Er-Tb) were grown epitaxially on (111)ZrO2(Y2O3) substrates using metal-organic chemical vapour deposition. Temperature and field dependences of magnetization were measured and analyzed for all samples and revealed weak ferromagnetic behavior below T = 120–140 K. The difference in electronic structure along with a distinct similarity in the crystal structure of hexagonal manganites RMnO3 and hexagonal orthoferrites RFeO3 are brought into focus in order to explain the results. Hexagonal orthoferrites are regarded as a promising family of multiferroics.

Multiferroicity in doped hexagonalLuFeO3

“…As both (100) and (101) reflections were observed at low temperature, the resolution-corrected integrated intensities were refined using a two-representation model with basis vectors of both the A 1 and A 2 representations, thereby allowing for rotation of the moments in the plane while requiring only two free parameters after scaling to the integrated intensities of several nuclear reflections. At 5 K the moments are found to be coherently rotated in the a-b plane 25 (5) • from the pure A 2 configuration toward the A 1 with m = 3.55 (9) could not be determined here and was thus fixed to zero in these refinements; this is consistent with a ferromagnetic moment less than 0.1μ B /Fe based upon recent studies of thin films [13][14][15][16], whose intensity is further suppressed by the structure factor for the special position of the transition metal species.…”

“…Recent ab initio calculations [12] have suggested that the closely related family of hexagonal ferrites such as LuFeO 3 (h-LFO) may exhibit greatly enhanced magnetic properties relative to their manganite counterparts due to enhanced exchange interactions, larger localized magnetic moments, and differences in the local electronic anisotropy between Mn 3+ and Fe 3+ . In fact, recent investigations of thin films of h-LFO demonstrate that magnetic order occurs as high as 150 K with the simultaneous appearance of a net ferromagnetic (FM) moment parallel to the ferroelectric axis [13][14][15][16] consistent with ab initio calculations [12]. To date, studies of this material have been limited to thin films as h-LuFeO 3 is metastable in bulk and instead forms the centrosymmetric and nonpolar orthorhombic Pbnm structure, precluding ferroelectricity [17].…”

Phase separation in LuFeO3 films

“…Hexagonal LuFeO 3 (h-LuFeO 3 ) is a multiferroic material that exhibits spontaneous electric and magnetic polarizations simultaneously. [1][2][3][4][5] It has been predicted that the magnetic dipole moment in h-LuFeO 3 can be switched by an electric field, 6 which is appealing for application in energy efficient information storage and processing. [7][8][9] Rather than h-LuFeO 3 , the orthorhombic crystallographic structure (o-LuFeO 3 ) is the thermodynamically stable bulk structure of LuFeO 3 with standard conditions, 10 meaning that the free energy of o-LuFeO 3 is lower than that of the h-LuFeO 3 .…”

Intrinsic magnetic properties of hexagonal LuFeO3 and the effects of nonstoichiometry

“…Using epitaxial stabilization, however, it is possible to make a metastable hexagonal polymorph of LuFeO 3 that is isostructural with YMnO 3 and other hexagonal rare-earth manganites. 21 In this hexagonal structure, LuFeO 3 has been measured to be both ferroelectric 22,23 and weakly ferromagnetic, [22][23][24] with first principles calculations predicting the ability to reverse the magnetization with a change in polarization. 25 It was recently reported that h-LuFeO 3 is antiferromagnetically ordered at room temperature with a canted antiferromagnetic ordering at T N = 130 K, 23 making it one of the few known room-temperature multiferroics (in this work we will refer to the onset of canted antiferromagnetic order, which is what we can measure, as the Néel temperature).…”