Size dependent Verwey transition

Size Dependence of Metal–Insulator Transition in Stoichiometric Fe3O4 Nanocrystals.
Jisoo Lee, Soon Gu Kwon, Je-Geun Park, and Taeghwan Hyeon
Nano Lett. 15, 4337 (2015)

Size dependence of T_V for Fe₃O₄ NCs. The contour plot represents the heat capacity data after removing the contribution of surfactant. The symbols mark the Verwey transition temperature (T_V) determined from three different types of measurements: heat capacity (green, C_P/T), conductance (blue, G), and magnetic moment (red, m). The size dependence of blocking temperature (T_B) is also plotted from the same magnetization measurement (black). The gray line is a guide to the eye for the size dependence of T_B.

 

Magnetic Interactions and Energy Barrier Enhancement in Core/Shell Bimagnetic Nanoparticles - The Journal of Physical Chemistry C (ACS Publications)

Magnetic Interactions and Energy Barrier Enhancement in Core/Shell Bimagnetic Nanoparticles.

Gabriel C. Lavorato, Davide Peddis, Enio Lima , Jr., Horacio E. Troiani, Elisabetta Agostinelli, Dino Fiorani, Roberto D. Zysler, and Elin L. Winkler

J. Phys. Chem. C 119, 15755 (2015) 

In this work, we studied the dynamic and static magnetic properties of ZnO-core/CoFe₂O₄-shell and CoO-core/CoFe₂O₄-shell nanoparticles. Both systems are formed by a core of ∼4 nm of diameter encapsulated in a shell of ∼2 nm of thickness. The mean blocking temperature changes from 106(7) to 276(5) K when the core is diamagnetic or antiferromagnetic, respectively. Magnetic remanence studies revealed the presence of weak dipolar interparticle interactions, where H_int is approximately −0.1 kOe for ZnO/CoFe₂O₄ and −0.9 kOe for CoO/CoFe₂O₄, playing a minor role in the magnetic behavior of the materials. Relaxation experiments provided evidence that the magnetization reversal process of CoFe₂O₄ is strongly dependent on the magnetic order of the core. At 10 K, activation volumes of ∼46(6) and ∼69(5) nm³ were found for CoO/CoFe₂O₄ and ZnO/CoFe₂O₄ nanoparticles, respectively, corresponding to one-third and one-fifth of the total shell volume. While the magnetic behavior of ZnO/CoFe₂O₄ nanoparticles is strongly affected by the surface disorder, the exchange coupling at the CoO/CoFe₂O₄ interface rules the magnetization reversal and the nanoparticles’ thermal stability by inducing a larger energy barrier and promoting smaller switching volume.

Diversity of Hyperthermia Response

A Single Picture Explains Diversity of Hyperthermia Response of Magnetic Nanoparticles.

Ivan Conde-Leboran , Daniel Baldomir, Carlos Martinez-Boubeta, Oksana Chubykalo-Fesenko, María del Puerto Morales, Gorka Salas, David Cabrera, Julio Camarero, Francisco J. Teran, and David Serantes

Journal of Physical Chemistry C 119, 15698 (2015)

 

Addressing the Control of NP arrangement and performance in Hyperthermia

Nano-objects for Addressing the Control of Nanoparticle Arrangement and Performance in Magnetic Hyperthermia.
Irene Andreu, Eva Natividad, Laura Solozábal, and Olivier Roubeau
ACS Nano, 9 1408 (2015)

One current challenge of magnetic hyperthermia is achieving therapeutic effects with a minimal amount of nanoparticles, for which improved heating abilities are continuously pursued. However, it is demonstrated here that the performance of magnetite nanocubes in a colloidal solution is reduced by 84% when they are densely packed in three-dimensional arrangements similar to those found in cell vesicles after nanoparticle internalization. This result highlights the essential role played by the nanoparticle arrangement in heating performance, uncontrolled in applications. A strategy based on the elaboration of nano-objects able to confine nanocubes in a fixed arrangement is thus considered here to improve the level of control. The obtained specific absorption rate results show that nanoworms and nanospheres with fixed one- and two-dimensional nanocube arrangements, respectively, succeed in reducing the loss of heating power upon agglomeration, suggesting a change in the kind of nano-object to be used in magnetic hyperthermia.

Magnetism on a curved nano-surface

Evolution of magnetism on a curved nano-surface.

D. G. Merkel, D. Bessas, Z. Zolnai, R. Rüffer, A. I. Chumakov, H. Paddubrouskaya, C. Van Haesendonck, N. Nagy, A. L. Tóth and A. Deák

Nanoscale 7, 12878 (2015)

Magnetic moment configuration calculated by micromagnetic simulation for (a) 26 Å, (b) 34.5 Å, (c) 48.5 Å and (d) 70.5 Å evaporated iron thickness on 25 nm diameter spheres. The blue color represents the magnitude of the z component while the red stands for the x–y in-plane component.

 

Size effects on EB in NiO NPs

Scrutinizing the role of size reduction on the exchange bias and dynamic magnetic behavior in NiO nanoparticles.
N Rinaldi-Montes, P Gorria, D Martínez-Blanco, A B Fuertes, L Fernández Barquín, I Puente-Orench and J A Blanco
Nanotechnology 26, 305705 (2015)

(a)–(d) Magnetic hysteresis loops for samples D2, D4 and D9 measured at selected temperatures, (a) 2, (b) 20, (c) 140 and (d) 300 K (that corresponding to a bulk NiO standard is included for the sake of comparison). (e)–(h) Enlarged views of the central part of the loops, evidencing the decrease in H_C and M_r with increasing temperature. The pictures inside (a)–(d) indicate the blocked/frozen (blue) or unblocked/unfrozen (red) regimes for the cores and shells, and correspond to samples D2 (top), D4 (middle) and D9 (bottom)