Giant negative thermal expansion in magnetic nanocrystals
- 19 October 2008
- journal article
- letter
- Published by Springer Science and Business Media LLC in Nature Nanotechnology
- Vol. 3 (12), 724-726
- https://doi.org/10.1038/nnano.2008.309
Abstract
Most solids expand when they are heated, but a property known as negative thermal expansion has been observed in a number of materials, including the oxide ZrW2O8 (ref. 1) and the framework material ZnxCd1−x(CN)2 (refs 2,3). This unusual behaviour can be understood in terms of low-energy phonons1,2,3,4,5,6, while the colossal values of both positive and negative thermal expansion recently observed in another framework material, Ag3[Co(CN)6], have been explained in terms of the geometric flexibility of its metal–cyanide–metal linkages7. Thermal expansion can also be stopped in some magnetic transition metal alloys below their magnetic ordering temperature, a phenomenon known as the Invar effect8,9, and the possibility of exploiting materials with tuneable positive or negative thermal expansion in industrial applications has led to intense interest in both the Invar effect and negative thermal expansion. Here we report the results of thermal expansion experiments on three magnetic nanocrystals—CuO, MnF2 and NiO—and find evidence for negative thermal expansion in both CuO and MnF2 below their magnetic ordering temperatures, but not in NiO. Larger particles of CuO and MnF2 also show prominent magnetostriction (that is, they change shape in response to an applied magnetic field), which results in significantly reduced thermal expansion below their magnetic ordering temperatures; this behaviour is not observed in NiO. We propose that the negative thermal expansion effect in CuO (which is four times larger than that observed in ZrW2O8) and MnF2 is a general property of nanoparticles in which there is strong coupling between magnetism and the crystal lattice.Keywords
This publication has 17 references indexed in Scilit:
- Colossal Positive and Negative Thermal Expansion in the Framework Material Ag 3 [Co(CN) 6 ]Science, 2008
- Nanoporosity and Exceptional Negative Thermal Expansion in Single‐Network Cadmium CyanideAngewandte Chemie-International Edition, 2008
- Negative thermal expansion and low-frequency modes in cyanide-bridged framework materialsPhysical Review B, 2005
- Unusual Low-Energy Phonon Dynamics in the Negative Thermal Expansion CompoundPhysical Review Letters, 2004
- Large Negative Magnetic Contribution to the Thermal Expansion in Iron-Platinum Alloys: Quantitative Theory of the Invar EffectPhysical Review Letters, 2003
- Phonon density of states and negative thermal expansion in ZrW2O8Nature, 1998
- Large Low Temperature Specific Heat in the Negative Thermal Expansion CompoundPhysical Review Letters, 1998
- Negative Thermal Expansion from 0.3 to 1050 Kelvin in ZrW 2 O 8Science, 1996
- Magnetism in cupric oxideJournal of Physics C: Solid State Physics, 1988
- A refinement of the crystal structure of copper(II) oxide with a discussion of some exceptional e.s.d.'sActa Crystallographica Section B: Structural Science, Crystal Engineering and Materials, 1970