Insulator–metal transition in Nd0.8Na0.2Mn(1−x)CoxO3 perovskites

The electric and magnetic properties of the perovskites Nd0.8Na0.2Mn(1−x)CoxO3 (0less-than-or-equals, slantxless-than-or-equals, slant0.2) prepared by the usual ceramic procedure were investigated. The insulator-to-metal-like (IM) transition, closely related to a ferromagnetic arrangement, was revealed for the composition of x=0.04 and a similar tendency was detected for x=0. The insulating behavior persists down to low temperatures for higher contents of cobalt ions in spite of the transition to the bulk ferromagnetism. The properties are interpreted in terms of the steric distortion, tilting of the Mn(Co)O6 octahedra and the double-exchange interactions of the type Mn3+–O2−–Mn4+and Mn3.5+δ–O2−–Co2+, respectively. Presence of antiferromagnetic domains in the ferromagnetic matrix for the most of cobalt-substituted samples is supposed

Lanthanum manganese perovskite nanoparticles as possible in vivo mediators for magnetic hyperthermia

Manganese perovskite La0.75Sr0.25MnO3 nanoparticles of the crystallite size 20–180 nm were prepared starting from citrate gel precursor by annealing in the range of 570–900 °C. It is shown that the decrease of the crystallite size leads to a gradual decrease of the magnetization and Curie temperature. The observed behaviour is a consequence of a non-collinear spin arrangement at the surface layer of crystallites, estimated to be of ~5 nm. Magnetic heating experiments were carried out with an aqueous stable suspension of a selected sample (Mit = 42 emu/g, Tc = 352 K) under an alternating field of Hmax=88mT, v = 108 kHz. The yielded values of specific absorption rate (SAR) were found to be larger than 500 W/gMn at 27 °C and 350 W/gMn at 37 °C

Lanthanum manganese perovskite nanoparticles as possible in vivo mediators for magnetic hyperthermia

Manganese perovskite La0.75Sr0.25MnO3 nanoparticles of the crystallite size 20–180 nm were prepared starting from citrate gel precursor by annealing in the range of 570–900 °C. It is shown that the decrease of the crystallite size leads to a gradual decrease of the magnetization and Curie temperature. The observed behaviour is a consequence of a non-collinear spin arrangement at the surface layer of crystallites, estimated to be of ~5 nm. Magnetic heating experiments were carried out with an aqueous stable suspension of a selected sample (Mit = 42 emu/g, Tc = 352 K) under an alternating field of Hmax=88mT, v = 108 kHz. The yielded values of specific absorption rate (SAR) were found to be larger than 500 W/gMn at 27 °C and 350 W/gMn at 37 °C

Magnetic heating by cobalt ferrite nanoparticles

In the quest for suitable materials for hyperthermia we explored the preparation and properties of nanoparticles of Co ferrite. The material was produced by coprecipitation from water solution of Co and Fe chlorides and afterwards annealed at 400, 600 and 800 °C. The resulting particles were characterized by XRD, TEM, Mössbauer spectroscopy, and dc and ac magnetometry. The heating experiments in ac magnetic fields of various amplitudes were performed with diluted systems of particles suspended in agarose gel and the results were interpreted on the basis of the ac magnetic losses measured at various temperatures. The increase of magnetic losses and consequently of the heating efficiency with increasing temperature is explained by the strong dependence of the constant of magnetocrystalline anisotropy of Co ferrite on temperature