Effect of chemical and hydrostatic pressures on structural and magnetic properties of rare-earth orthoferrites: a first-principles study

Abstract

The dependence of structural and magnetic properties of rare-earth orthoferrites (in their Pbnm ground state) on the rare-earth ionic radius is systematically investigated from first principles. The effects of this 'chemical pressure' on lattice constants, Fe-O bond lengths, Fe-O-Fe bond angles and Fe-O bond length splittings are all well reproduced by these ab initio calculations. The simulations also offer novel predictions (on tiltings of FeO6 octahedra, cation antipolar displacements and weak magnetization) to be experimentally checked. In particular, the weak ferromagnetic moment of rare-earth orthoferrites is predicted to be a linear function of the rare-earth ionic radius. Finally, the effects of applying hydrostatic pressure on structural and magnetic behavior of SmFeO3 is also studied. It is found that, unlike previously assumed, hydrostatic pressure typically generates changes in physical properties that are quantitatively and even qualitatively different from those associated with the chemical pressure.

Properties of rare-earth iron garnets from first principles

“…One can first see that these cubic lattice parameters for the Type (1) calculation (i.e., when f electrons of the R ions are treated as core electrons) all nearly linearly decrease when r R decreases within the Lanthanide series, as consistent with the concept of "chemical pressure" that is typically given to the variation of the rare-earth ionic radius in various R-based families (see, e.g., Refs. [12,22] and references therein). Interestingly, the only element that does not belong to the Lanthanide series, that is Y , is predicted to adopt a cubic lattice constant that deviates upward from this linear behavior.…”

Spin reorientation and disordered rare earth magnetism in Ho2FeCoO6

“…The well-studied end members of Ho 2 FeCoO 6 are orthorhombic HoFeO 3 and HoCoO 3 [13,14] which are weak ferromagnets with the rare earth Ho 3+ ordering magnetically at ≈ 4.1 K and ≈ 3 K respectively [15,13]. The orthoferrites RFeO 3 generally have high Néel temperatures of the order of ∼ 700 K [16,17] and in bulk form are not multiferroic though, recent theoretical calculations on thin films show the emergence of electric polarization with the application of strain [18]. In the orthoferrite HoFeO 3 spin reorientation of the Fe moments is reported in the temperature ranges 50 K -58 K [13] and 34 K -54 K [19], caused by Ho 3+ -Fe 3+ interactions and competing Zeeman and van Vleck contribution to the anisotropy that initiates the Fe spin reorientation.…”

Origin of the magnetization and compensation temperature in rare-earth orthoferrites and orthochromates

“…13 Others propose that it involves all the possible magnetic orderings (i.e., ferromagnetism, as well as G-, A-and C-types of antiferromagnetism) of this Fe/Cr sublattice. 14 We are also still missing a discussion on how the peculiarities of the P bnm crystal structure -i.e., in-phase and antiphase oxygen octahedral tiltings and antiferroelectricity 15,16 -may also affect the occurrence and nature of this effective magnetic field. This possibility is especially obvious when one notes that the magnetic ordering of the B-sublattice of ABO 3 perosvkites has been shown to depend on the octahedral tilting pattern, 17 or that antiferroelectricity has been predicted to mediate magnetoelectric switching (i.e., reversal of the magnetic order parameter by application of electric field) in some perovskites.…”