BLANCO MARÍA CECILIA
Congresos y reuniones científicas
Título:
Influence of the B site ordering on the magnetic properties in the new La3Co2MO9 double perovskites with M = Nb or Ta
Autor/es:
FUERTES V. C.; BLANCO M. C.; D. G. FRANCO; DE PAOLI J. M.; E. V. PANNUNZIO MINER; SÁNCHEZ R.D.; FERNÁNDEZ-DÍAZ, M. T.; CARBONIO R. E
Lugar:
Ciudad de Buenos Aires, Buenos Aires, Argentina
Reunión:
Congreso; At the frontiers of condensed matter IV: Current trnds and novel materials.; 2008
Institución organizadora:
Centro Atómico Constituyentes
Resumen:
Perovskite compounds are very interesting materials because of their potential technological applications. The ideal cubic
perovskite structure can be seen like a three-dimensional corner-sharing network of BO6 octahedra, with a large A-cation
occupying the cuboctahedral cavities. Double perovskites are formed with the general formula A2B?B?O6 were ions B and B,
in the ideal case, occupy different crystallographic sites. Usually, however, there is a certain degree of anti-site disorder, where
a fraction of B occupies the B sites and vice versa. Usually, A is an alkali-earth ion, like Ca2+, Sr2+, Ba2+. However, there
are few reports of double perovskite materials in which the A site ion has been totally replaced by a small lanthanide Ln3+.
Magnetism in these compounds can be achieved when de B site ion is a transition metal cation with unmatched electrons.
Magnetic properties, like ferromagnetism, or ferrimagnetism, in double perovskites are strongly dependents on their B cations
order-disorder relationship. In the present work we describe the synthesis, structures and magnetic characterization of a new
perovskite type family: La3Co2MO9 with M = Nb, Ta. These phases were synthesized as polycrystalline powders by both
standard ceramic and sol gel method, this last one by a tartrate-precursor decomposition. Their crystallographic formula
can be written as La3(Co)2d(CoM)2cO9 for samples synthesized by solid state and as La3(Co2-xMx)2d(CoxM1-x)2cO9
forthose synthesized by the sol-gel method. Structural analysis was made through Rietveld refinement from XRPD and
NPD data. All are insulator monoclinic double perovskites and can be well characterized in P 21/n SG. Anti-site disorder
is noticeable larger in the sol-gel compounds case. Magnetic measurements were made in a commercial SQUID in the 10
300 K temperature range, with the objective to understand the effect that causes this disorder on the magnetic properties of
these materials. M vs T measurements indicated that samples synthesized by solid state are ferromagnetic with TC c.a. 60
K, while those synthesized by the sol-gel method are antiferromagnetic materials with TN c.a. 20 K. The solid state method
synthesized compounds have shown to be more B site ordered than sol-gel synthesized compounds. We assign the different
magnetic behaviours displayed by both compounds to these differences in antisite disorder. The refined magnetic cells are
in agreement with magnetic measurements in both, ferromagnetic and antiferromagnetic cases.
perovskite structure can be seen like a three-dimensional corner-sharing network of BO6 octahedra, with a large A-cation
occupying the cuboctahedral cavities. Double perovskites are formed with the general formula A2B?B?O6 were ions B and B,
in the ideal case, occupy different crystallographic sites. Usually, however, there is a certain degree of anti-site disorder, where
a fraction of B occupies the B sites and vice versa. Usually, A is an alkali-earth ion, like Ca2+, Sr2+, Ba2+. However, there
are few reports of double perovskite materials in which the A site ion has been totally replaced by a small lanthanide Ln3+.
Magnetism in these compounds can be achieved when de B site ion is a transition metal cation with unmatched electrons.
Magnetic properties, like ferromagnetism, or ferrimagnetism, in double perovskites are strongly dependents on their B cations
order-disorder relationship. In the present work we describe the synthesis, structures and magnetic characterization of a new
perovskite type family: La3Co2MO9 with M = Nb, Ta. These phases were synthesized as polycrystalline powders by both
standard ceramic and sol gel method, this last one by a tartrate-precursor decomposition. Their crystallographic formula
can be written as La3(Co)2d(CoM)2cO9 for samples synthesized by solid state and as La3(Co2-xMx)2d(CoxM1-x)2cO9
forthose synthesized by the sol-gel method. Structural analysis was made through Rietveld refinement from XRPD and
NPD data. All are insulator monoclinic double perovskites and can be well characterized in P 21/n SG. Anti-site disorder
is noticeable larger in the sol-gel compounds case. Magnetic measurements were made in a commercial SQUID in the 10
300 K temperature range, with the objective to understand the effect that causes this disorder on the magnetic properties of
these materials. M vs T measurements indicated that samples synthesized by solid state are ferromagnetic with TC c.a. 60
K, while those synthesized by the sol-gel method are antiferromagnetic materials with TN c.a. 20 K. The solid state method
synthesized compounds have shown to be more B site ordered than sol-gel synthesized compounds. We assign the different
magnetic behaviours displayed by both compounds to these differences in antisite disorder. The refined magnetic cells are
in agreement with magnetic measurements in both, ferromagnetic and antiferromagnetic cases.
