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Tailoring surface phase transition and magnetic behaviors in BiFeO3 via doping engineering.

ABSTRACT: The charge-spin interactions in multiferroic materials (e.g., BiFeO3) have attracted enormous attention due to their high potential for next generation information electronics. However, the weak and deficient manipulation of charge-spin coupling notoriously limits their commercial applications. To tailor the spontaneous charge and the spin orientation synergistically in BiFeO3 (BFO), in this report, the 3d element of Mn doping engineering is employed and unveils the variation of surface phase transition and magnetic behaviors by introducing chemical strain. The spontaneous ferroelectric response and the corresponding domain structures, magnetic behaviors and spin dynamics in Mn-doped BFO ceramics have been investigated systematically. Both the surface phase transition and magnetization were enhanced in BFO via Mn doping. The interaction between the spontaneous polarization charge and magnetic spin reorientation in Mn-doped BFO are discussed in detail. Moreover, our extensive electron paramagnetic resonance (EPR) results demonstrate that the 3d dopant plays a paramount role in the surface phase transition, which provides an alternative route to tune the charge-spin interactions in multiferroic materials.

SUBMITTER: Yan F

PROVIDER: S-EPMC4360736 | biostudies-other | 2015

REPOSITORIES: biostudies-other

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Project description:Dopants in gold nanoclusters have been proved to mediate the intrinsic electronic properties of homo-clusters. In this work, we report the precise synthesis of atomically precise Au8Ag3(PPh3)7Cl3 alloy nanoclusters with multiple Ag dopants for the first time. Their structure was resolved by single-crystal X-ray crystallography. Au8Ag3(PPh3)7Cl3 nanoclusters possessed a similar structure topology to the well-known Au11(PPh3)7Cl3 nanoclusters. It is observed that the three Ag atoms were fixed at the cluster surface and bound selectively with the chlorine ligands in a C3-axis manner. The alloy nanoclusters exhibited a closed-shell electronic structure (i.e., 8(Au 6s1) + 3(Ag 5s1) - 3(Cl) = 8e), as evidenced by electrospray ionization-mass spectrometry (ESI-MS). The photothermodynamic stability of alloy clusters was remarkably improved (e.g., full decomposition after 7 days under sunlight irradiation vs. 3 days for Au11(PPh3)7Cl3 clusters). DFT calculations indicated that the Ag dopants in a C3-axis manner could obviously delocalize the electrons of Au to the orbitals of P atoms and then mediate the electronic property of the clusters. Shrinkage of the HOMO-LUMO gap to 1.67 eV of Au8Ag3(PPh3)7Cl3 was observed as compared with that of homo-nanoclusters of Au11(PPh3)7Cl3 (2.06 eV). The electrochemical gap of Au8Ag3(PPh3)7Cl3 alloy nanoclusters was 1.272 V, which was higher than that of Au11(PPh3)7Cl3 nanoclusters, which indicated higher electrochemical stability, as evidenced by the differential pulse voltammetry (DPV) method. Au8Ag3(PPh3)7Cl3 clusters exhibited three specific photoluminescence peaks at 405, 434 and 454 nm. AuAg alloy clusters exhibited twofold greater activity than homo gold clusters in the photooxidation of benzylamine, which was mainly due to the unique electronic properties of the alloy clusters. Controllable heteroatom doping engineering is a powerful method to tune the electronic properties of clusters, and then improve their photothermodynamic and electrochemical stability simultaneously for potential photocatalytic applications.

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Tailoring surface phase transition and magnetic behaviors in BiFeO3 via doping engineering.

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