1 1 5 I H I G H L I G H T S 2 0 2 1
fashion (Figure 94b-c). The A layer is composed of pure Pb2+ and B is the mixture of Pb2+ and Pb4+ with a ratio of 1:3. Consequently, two FeO6 octahedra with different symmetries are sandwiched between different interlayers of A B and B B. This renders PbFeO3 unique in all the reported charge-order perovskite oxides.
Strong antiferromagnetic Fe3+-Fe3+ coupling results in a canted G-type spin-ordering at 600 K in PbFeO3, where the spins are along the a-axis and a net magnetic moment is formed along the c-axis (Figure 95). When the temperature decreases to 418 K, a spin reorientation (SR) transition is found to occur, leading to the formation of a
collinear antiferromagnetic structure with spins parallel to the b-axis. In RFeO3 (R = rare earth) family, the SR transitions present often at temperatures below 200 K due to the single-ion magnetic anisotropy of the R ions. However, in PbFeO3, both Pb
2+ and Pb4+ cations located at the A-site are nonmagnetic, which excludes the anisotropic magnetic interactions between A- and B-site. Besides, the temperature-dependent diffraction experiments confirm that there is no crystal structure transition. Based on further theoretical investigations, the origin of SR in PbFeO3 is determined to be the anisotropic energy competition between the two kinds of Fe3+ magnetic sublattices generated by the peculiar A-site charge ordering.
PRINCIPAL PUBLICATION AND AUTHORS
Observation of novel charge ordering and spin reorientation in perovskite oxide PbFeO3, X. Ye (a,b), J. Zhao (a,b), H. Das (c,d), D. Sheptyakov (e), J. Yang (e), Y. Sakai (f,c), H. Hojo (g), Z. Liu (a,b), L. Zhou (a,b), L. Cao (a), T. Nishikubo (c), S. Wakazaki (c), C. Dong (a,b), X. Wang (h), Z. Hu (h), H-J. Lin (i), C-T. Chen (i), C. Sahle (j), A. Efiminko (j), H. Cao (k), S. Calder (k), K. Mibu (l), M. Kenzelmann (e), L.H. Tjeng (h), R. Yu (a,b,d), M. Azuma (c,f), C. Jin (a,b,m), Y. Long (a,b,m), Nat. Commun. 12, 1917, (2021); https:/doi.org/10.1038/s41467-021-22064-9 (a) Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing (China) (b) School of Physical Sciences, University of Chinese Academy of Sciences, Beijing (China) (c) Laboratory for Materials and Structures, Tokyo Institute of Technology, Yokohama, Kanagawa (Japan) (d) Tokyo Tech World Research Hub Initiative (WRHI), Institute of Innovative Research, Tokyo Institute of Technology, Yokohama,
Kanagawa (Japan) (e) Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, Villigen (Switzerland) (f) Kanagawa Institute of Industrial Science and Technology, Ebina (Japan) (g) Department of Advanced Materials and Engineering, Faculty of Engineering Sciences, Kyushu University, Kasuga (Japan) (h) Max-Planck Institute for Chemical Physics of Solids, Dresden (Germany) (i) National Synchrotron Radiation Research Center, Hsinchu, Taiwan, (ROC) (j) ESRF (k) Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee (USA) (l) Graduate School of Engineering, Nagoya Institute of Technology, Nagoya (Japan) (m) Songshan Lake Materials Laboratory, Dongguan, Guangdong (China)
Emerging 2D magnetic states in a graphene based-monolayer of EuC6
The discovery of two-dimensional (2D) magnetism offers unprecedented opportunities to address fundamental problems in condensed matter physics, with upcoming applications in ultra-compact spintronics and quantum computing. Further progress hinges on the deep understanding of the electronic and magnetic properties of 2D magnets at the atomic scale, exploiting the element selectivity of XMCD.
The quest for two-dimensional (2D) magnetism has a rich history , from rather pessimistic theoretical assessments to experimental studies of ultrathin films of magnetic metals and to discoveries of 2D ferromagnetism in layered materials scaled down to monolayers. The ever-growing material landscape of 2D magnets lacks carbon-based systems, prominent in other areas of 2D research. Attaining strong 2D magnetism, however, seemed challenging
or even out of reach. After all, carbon is not best known for its magnetic properties. However, magnetism into carbon-based structures can be introduced extrinsically, as demonstrated by the integration of graphene with the ferromagnetic semiconductor EuO . One may anticipate that the successful extrinsic action of Eu in forging graphene magnetism is replicated once Eu and graphene make a stoichiometric compound.
Bulk EuC6, graphite functionalised by Eu 2+ magnetic
ions carrying a large magnetic moment of 7 µB, exhibits antiferromagnetic order. In contrast, its single monolayer, comprising flat sheets of Eu and graphene (Figure 96a), was shown to behave as a 2D ferromagnet, but the saturation magnetic moment was found to be significantly lower than that expected for the half-filled f-shells of Eu2+ ions . Traditional magnetisation measurements do not reveal a cause for reduced magnetic moments in monolayer EuC6 the notable diamagnetism of the substrate limits the studies to relatively low magnetic fields. Quite remarkably, the functionalisation by Eu does not destroy the electron