Variation of structural and magnetic properties with composition in the (Co{sub x}Ni{sub 1-x}){sub 1.5}[Fe(CN){sub 6}]{center_dot}zH{sub 2}O series

Journal Article · Fri Jun 01 00:00:00 EDT 2007 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.75.224419· OSTI ID:20951533

Kumar, Amit; Yusuf, S M; Keller, L; Yakhmi, J V; Srivastava, J K; Paulose, P L ^[1]

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1. Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)

Structural and magnetic properties of the compounds (Co{sub x}Ni{sub 1-x}){sub 1.5}[Fe(CN){sub 6}]{center_dot}zH{sub 2}O (0{<=}x{<=}1) have been studied by x-ray and neutron-diffraction, dc magnetization, infrared (IR), and Moessbauer spectroscopic techniques. All studied compounds of the series crystallize in the fcc structure with Fm3m space group. Detailed structural studies by x-ray diffraction followed by Moessbauer and IR studies reveal disordered structures with the presence of Co/Ni-N{identical_to}C-Fe-C{identical_to}N-Co/Ni- and Co/Ni-C{identical_to}N-Fe-N{identical_to}C-Co/Ni-type linear chains along the edges of the unit-cell cube. Neutron-diffraction patterns of all the members of the series have diffuse scattering and a broad peaklike feature at the (100) position which is forbidden under the Fm3m space group. The reverse Monte Carlo simulations of this diffuse scattering, present due to structural disorders, indicate a correlated substitution of water molecules at the empty Fe(CN){sub 6} sites. The magnetic ordering temperature decreases with increasing amount of the Co substitution and it is minimum for the x=0.75 compound. Field-dependent magnetization measurements at 1.5 K and up to a maximum field of 70 kOe reveal that all compounds (except x=1) of the series are ferromagnetic with positive exchange interactions between the nearest-neighbor low-spin Co{sup 2+}(S=(1/2))/Ni{sup 2+} (S=1) and the mixed-spin Fe{sup 3+} [low-spin (S=(1/2)) and high-spin (S=(5/2))] ions. However, the end compound Co{sub 1.5}[Fe(CN){sub 6}]{center_dot}zH{sub 2}O (x=1) of the series is a ferrimagnet with negative exchange interactions between the high-spin Co{sup 2+} (S=(3/2)) and the low-spin Fe{sup 3+} (S=(1/2)) and also between the low-spin Co{sup 2+} (S=(1/2)) and the high-spin Fe{sup 3+} (S=(5/2)) ions. The observed dip in the values of the lattice parameter, transition temperature, saturation magnetization, coercive field, and remanence around x=0.75 is ascribed due to the presence of the largest amount of structural disorder around that composition. Neutron-diffraction patterns of the compounds, down to 1.5 K, do show negligibly small magnetic contribution to the fundamental (nuclear) Bragg reflections, however, these contributions are more than one order of magnitude smaller than the modulated diffuse scattering contributions. The effects of structural disorder, due to the presence of vacancies of the Fe(CN){sub 6} and uncoordinated water molecules, and the quenched disorder, due to random substitution of Ni by Co at the (0, 0, 0) site, on the magnetic ordering in these molecular magnetic compounds have been brought out.

• OSTI ID: 20951533
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 75, Issue 22; Other Information: DOI: 10.1103/PhysRevB.75.224419; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BRAGG REFLECTION
CARBON NITRIDES
COBALT IONS
COMPUTERIZED SIMULATION
CYANIDES
DIFFUSE SCATTERING
EXCHANGE INTERACTIONS
FCC LATTICES
INFRARED SPECTRA
IRON IONS
MAGNETIC PROPERTIES
MAGNETIZATION
MONTE CARLO METHOD
NEUTRON DIFFRACTION
NICKEL IONS
SPACE GROUPS
SPIN
TRANSITION TEMPERATURE
VACANCIES
X-RAY DIFFRACTION