Spontaneous atomic ordering and magnetism in epitaxially stabilized double perovskites

Abstract

We have studied the atomic ordering of B-site transition metals and magnetic properties in the pulsed-laser deposited films of La 2 CrFeO 6 (LCFO) and La 2 VMnO 6 (LVMO), whose bulk materials are known to be single perovskites with random distribution of the B-site cations.Despite similar ionic characters of constituent transition metals in each compound, the maximum B-site order attained was surprisingly high, ~90% for LCFO and ~80% for LVMO, suggesting a significant role of epitaxial stabilization in the spontaneous ordering process. Magnetization and valence state characterizations revealed that the magnetic ground state of both compounds was coincidently ferrimagnetic with saturation magnetization of ~2μ B per formula unit, unlike those predicted theoretically. In addition, they were found to be insulating with optical band gaps of 1.6 eV and 0.9 eV for LCFO and LVMO, respectively. Our results present a wide opportunity to explore novel magnetic properties of binary transition-metal perovskites upon epitaxial stabilization of the ordered phase.

Enhanced spontaneous polarization in double perovskite Bi2FeCrO6 films

“…On account of the magnetic moments of Fe 3+ (5 μB) and Cr 3+ (3 μB), antiferromagnetic B ‐site ordered arrangement leads to a net magnetic value of 2 μB per formula unit, corresponding to ~160.5 emu/cm 3 . For partially ordered BFCO, the relationship between saturation magnetization and Fe/Cr ordering can be described by the equation: M s = (2‐4AS) μB/fu (where AS refers to antisite defects) . So, the M s of completely ordered BFCO thin films will be 2 μB/fu and that of the completely disordered phase should be zero.…”

“…It was reported that the bandgap of the BFCO films is strongly correlated with the B ‐site cation ordering, and E g varies between 1.4 and 2.6 eV as the R value decreases . However, given the low X‐ray scattering contrast between the Fe 3+ and Cr 3+ , it was recently argued that the observation of a superstructure is not a sufficient proof of B ‐site ordering in double perovskites, and in fact the truly B ‐site ordered double perovskite has relatively lower R value less than 1%, for example La 2 FeCrO 6 film deposited on (111)‐oriented STO substrate …”

Challenges in Sr2FeMoO6−δ Thin Film Deposition

“…PLD synthesis of double perovskite oxides requires tuning of the different oxidation behavior of transition metals . For the deposition of oxide thin films exhibiting a preselected perovskite phase or a B‐site ordering in double perovskites, the main two parameters of the growing film environment, oxygen partial pressue p O2 and substrate temperature T s , are usually adjusted to provide conditions favorable for the formation of the desired film structure . B‐site ordering is known to become stable only at a large‐enough size and a valence difference of the B′ and B″ cations of about 15…20 pm and 2.5…3, respectively .…”

“…B‐site ordering is known to become stable only at a large‐enough size and a valence difference of the B′ and B″ cations of about 15…20 pm and 2.5…3, respectively . PLD favors a kinetically driven spontaneous ordering where the driving force is the difference in ionic radii and the oxidation states of the two B‐site cations . Here, on completion of deposition the films should be quenched to room temperature to freeze the ion positions in the lattice, preserving the achieved cation ordering.…”

Interface‐Coupled BiFeO3/BiMnO3 Superlattices with Magnetic Transition Temperature up to 410 K

“…However, this concept has not been widely realized due to the lack of cation ordering as a result of negligible differences in ionic valences and ionic radii. [11][12][13][14][15] On the other hand, disordered double perovskites (notably BiFe 0.5 Mn 0.5 O 3 (BFMO) and Bi 2 CoMnO 6 (BCMO)) show a strongly enhanced T C albeit with lower magnetic moment than expected for the ordered structure. [ 16,17 ] Pálová et al extended the idea of ordered double perovskites by theoretically studying BFMO with an ordered nanoscale checkerboard structure (NCB-BFO/BMO, see Figure 1 a), i.e., columnar B -site ordering.…”