Evidence of Robust Half-Metallicity in Strained Manganite Films

Abstract

We investigated the relationship between ferromagnetism and metallicity in strained La 0.67 Ca 0.33 MnO 3 films grown on lattice-mismatched NdGaO 3 (001) by means of spectroscopic techniques directly sensitive to the ferromagnetic state, to the band structure, and to the chemical state of the atoms. In this system, the ferromagnetic metallic (FMM) phase spatially coexists with an insulating one in most of the phase diagram. First, the observation of an almost 100% spin polarization of the photoelectrons at the Fermi level in the fundamental state provides direct evidence of the half-metallicity of the FMM phase, a result that has been previously observed through direct probing of the valence band only on unstrained, phase-homogeneous La 0.67 Sr 0.33 MnO 3 . Second, the spin polarization results to be correlated with the occupancy at the Fermi level for all the investigated temperature regimes. These outcomes show that the half-metallic behavior predicted by a double-exchange model persists even in phase-separated manganites. Moreover, the correlation between metallicity and ferromagnetic alignment is confirmed by X-ray magnetic circular dichroism, a more bulk-sensitive technique, allowing one to explain transport properties in terms of the conduction through aligned FMM domains.

Uniaxial Strain and Hydrostatic Pressure Engineering of the Hidden Magnetism in La1–xCaxMnO3 (0 ≤ x ≤ 1/2) Thin Films

“…At 1.5 GPa, the reduced ε b fails to stabilize an AFI state. The monoclinic AFI phase partially melts into the orthorhombic FMM phase, and accommodation strain forms at their interfaces, which could involve the formation of spatially inhomogeneous PS states. − ,− As shown in Figure b, at 3.2 GPa, the FMM phase dominates, but a small volume fraction of AFI remains, which is similar to that of LCMO/KTO at 2.6 GPa (see Figure S11). Based on an estimated pressure dependence of strain, compressive stress induced by 3.2 GPa is calculated to be about 1%.…”

“…Different symmetries of epitaxial strain can also induce quite dissimilar octahedral distortions, orbital orderings, and structural/magnetic domain morphologies. − In general, epitaxial strains can anisotropically change the atomic spacing along the in-plane and out-of-plane directions, and on the contrary, hydrostatic pressure compresses the lattice isotropically. − Therefore, the hydrostatic pressure and epitaxial strain could be considered as complementary tuning knobs. Manganite films have attracted much attention, arising from their colossal magnetoresistance, phase separation (PS), charge/orbital/spin ordering, and half-metal feature. ,, However, utilizing hydrostatic pressure and epitaxial strain cooperatively to engineer the structural/octahedral distortions of manganite thin films has rarely been addressed.…”

“…For intermediate-bandwidth La 1– x Ca x MnO 3 (LCMO) system, the Jahn–Teller distortion, which is typically coupled to Mn 3+ , competes with the double-exchange interaction, resulting in complex phase diagrams. − A bulk ferromagnetic metallic (FMM) state occurs in ∼1/5 ≤ x < 1/2 . By applying external perturbations, such as magnetic field ( H ), hydrostatic pressure ( P ), as well as epitaxial strain, LCMO may overcome energy barriers to reach a hidden phase in a complex free-energy landscape. − In contrast to the biaxially strained antiferromagnetic insulating (AFI) phase in LCMO films grown on SrTiO 3 (STO) substrates, it is found that utilizing anisotropic strain is much effective in inducing a charge-ordered AFI phase and PS in LCMO/NGO thin films at x = 1/3. − However, what is the difference between anisotropically and biaxially strained AFI phases and their associated orbital orderings? And can we extend the AFI ground state to lower doping levels in LCMO films, even at 0 ≤ x ≤ 1/2, and thus obtain an extended AFI phase diagram?…”

“…And can we extend the AFI ground state to lower doping levels in LCMO films, even at 0 ≤ x ≤ 1/2, and thus obtain an extended AFI phase diagram? Considering that both the hydrostatic pressure and epitaxial strain are effective tuning knobs, ,,− for the first time we try to use them cooperatively to tune the Jahn–Teller distortion and magnetic/electrical properties. These endeavors will provide valuable insights into the relation between local structure, electronic correlation, long-range order, and their physical properties. − …”

Formation and Etching of the Insulating Sr‐Rich V5+ Phase at the Metallic SrVO3 Surface Revealed by Operando XAS Spectroscopy Characterizations

“…Transition metal oxides are widely studied due to their broad range of versatile functionalities arising from the complex interplay between charge, orbital, spin, and lattice degrees of freedom. [ 1–6 ] In this family, it was shown that some composition present two antagonist properties at the same time: high electrical conductivity and visible‐range optical transparency. This class of materials is called transparent conductive oxide (TCO).…”