Magnetic ordering in La1.5Ca0.5CoO4 revealed by resonant magnetic x-ray scattering and neutron diffraction

DOI: 10.1103/PhysRevB.103.184422

Authors: G. Subias (CSIC-Universidad de Zaragoza; Universidad de Zaragoza) , J. Blasco (CSIC-Universidad de Zaragoza; Universidad de Zaragoza) , Javier Herrero-Martin (ALBA Synchrotron Light Source) , J. A. Rodríguez-Velamazán (Institut Laue-Langevin) , M. Valvidares (ALBA Synchrotron Light Source) , R. Fan (Diamond Light Source) , P. Steadman (Diamond Light Source) , J. García (CSIC-Universidad de Zaragoza; Universidad de Zaragoza)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review B , VOL 103

State: Published (Approved)
Published: May 2021
Diamond Proposal Number(s): 19996

Abstract: We report a comprehensive study on the magnetic ground state of La 1.5 Ca 0.5 Co O 4 combining single crystal neutron diffraction and resonant magnetic x-ray scattering at the Co L 2 , 3 edges. Three single-crystal samples obtained from the same boule were investigated exhibiting magnetic phase transitions from a high-temperature paramagnetic phase to an antiferromagnetic phase at T N ≈ 52 K . Single crystal neutron diffraction reveals that the crystal structure at room temperature shows an orthorhombic A -centered lattice but with a and b axes almost equal in length. The structural phase transition (charge-ordering-like) from the parent tetragonal cell takes place above 523 K into the space group A 2 m m where two nonequivalent compressed and expanded Co O 6 octahedra are ordered showing a checkerboard pattern in the a b plane. The charge segregation between the nonequivalent Co sites is about 0.4(1) electrons. Resonant magnetic x-ray reflections indexed as ( 1 / 4 , 1 / 4 , 0 ) t , ( 1 / 4 , 1 / 4 , 1 ) t , and ( 1 / 4 , 1 / 4 , 1 / 2 ) t in the parent tetragonal cell were observed at low temperature at the Co L 2 , 3 -edge energy range. The resonant spectral shape, with a noticeable absence of any resonant enhancement at the Co L 2 edge, indicates that only Co 2 + -like ions participate in the magnetic ordering. The polarization analysis discloses that the orientation of Co magnetic moments is the same for the three magnetic orders and they are long-range ordered along the diagonal in the a b plane of the parent tetragonal cell with a slight tilt in the c axis. Despite the onset temperatures for the three resonant magnetic reflections being the same, ≈ 55 K , different thermal behavior is observed between ( 1 / 4 , 1 / 4 , 1 / 2 ) t and ( 1 / 4 , 1 / 4 , L ) t ( L = integer ) reflections whose intensities maximize at different temperatures, suggesting the coexistence of two magnetic arrangements. Moreover, the intensity of the ( 1 / 4 , 1 / 4 , 1 / 2 ) t magnetic reflection is at least ten times larger than that of the ( 1 / 4 , 1 / 4 , L ) t ( L = integer ) ones. On the other hand\, neutron diffraction measurements only detect a single type of antiferromagnetic ordering following the propagation vector k = ( 1 / 4 , 1 / 4 , 1 / 2 ) t that involves half of the Co atoms in the unit cell. We conclude that the bulk magnetic order in La 1.5 Ca 0.5 Co O 4 corresponds then to this propagation vector k = ( 1 / 4 , 1 / 4 , 1 / 2 ) t while ( 1 / 4 , 1 / 4 , 0 ) t and ( 1 / 4 , 1 / 4 , 1 ) t magnetic reflections correspond to a minority magnetic phase that must be due to changes in the oxygen stoichiometry near the surface.

Journal Keywords: Antiferromagnetism; Magnetic order; Single crystal materials; Neutron diffraction; X-ray resonant magnetic scattering

Diamond Keywords: Antiferromagnetism

Subject Areas: Materials, Physics


Instruments: I10-Beamline for Advanced Dichroism

Other Facilities: BOREAS at ALBA

Added On: 25/05/2021 09:54

Discipline Tags:

Quantum Materials Hard condensed matter - electronic properties Physics Magnetism Materials Science Perovskites Metallurgy

Technical Tags:

Scattering Resonant Soft X-ray Scattering (RSXS)