Giant negative thermal expansion in magnetic nanocrystals

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 phonons, 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 linkages. Thermal expansion can also be stopped in some magnetic transition metal alloys below their magnetic ordering temperature, a phenomenon known as the Invar effect, 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.

Negative thermal expansion materials: technological key for control of thermal expansion

“…The magnetovolume effect is commonly observed for magnetic metals of various kinds aside from Invar, including Laves phase intermetallics such as YMn 2 [43,44], Th 2 Zn 17 -type intermetallics such as Tm 2 Fe 16 Cr [45,46,47], and manganese antiperovskites Mn 3 AX (A represents transition metals or semiconducting element; X denotes C and N). Recently, large NTE related to magnetism has been discovered in CuO nanoparticles [48].…”

Synthesis of copper/copper oxide nanoparticles by solution plasma

“…Moreover, many recent efforts have been directed toward the fabrication of nanocrystalline CuO to enhance its performance [3][4][5][6] and develop new functions. 7,8 Metallic nanoparticles of copper attract attention not only in the scientific field but also in industry because of their application in electronic devices such as printed circuit boards [9][10][11] and multilayer ceramic capacitors. 12,13 Conventionally, copper/copper oxide nanoparticles have been produced by gas-phase and liquid-phase methods, however, both methods face great challenges.…”

Local Structural Distortion Induced Uniaxial Negative Thermal Expansion in Nanosized Semimetal Bismuth

“…Unlike doping method, size effect recently has been proved to be another effective way to adjust the thermal expansion behaviors 8, 9, 10, 11. Because of the presence of dangling bonds, defects, and quantum correlation effects in nanosized metal or semimetal, some abnormal thermal expansion behaviors have been reported 12, 13.…”