日本語フィールド
著者：X.G. Zheng題名：
Giant negative thermal expansion in magnetic nanocrystals発表情報：SPring-8 Research Frontiers 巻: 2008キーワード：概要：Giant negative thermal expansion in magnetic nanocrystals抄録：Most solids expand when they are heated but a property known as negative thermal expansion (NTE) has been observed in a number of materials, including the oxide ZrW2O8 (1) and the framework material ZnxCd1-x(CN)2 (2). 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], has been explained in terms of the geometric flexibility of its metal-cyanide-metal linkages (3). 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 tunable positive or negative thermal expansion in industrial applications has led to intense interest in both the Invar effect and NTE.
Here we report our recent finding of giant negative thermal expansion in magnetic nanocrystals of CuO and MnF2 (4). The cupric oxide, CuO, is a unique transition metal mono oxide that was clarified by us to show strong charge-spin-lattice coupling and ferroelectric properties below its magnetic (antiferromagnetic) transition (5). This strong charge-spin-lattice coupling recently receives intense attention and is renamed by the term “multiferroics”. Our previous structure study suggested small anomalies in the lattice parameters at its magnetic transition temperatures (Néel temperature TN) and disappearance of thermal expansion below TN (i.e., zero thermal expansion). CuO fine particles with sizes narrowly distributed around ~5 nm were prepared by ball-milling from large (~cm) pure single crystals grown by a chemical vapour transport method. The high-resolution TEM image suggests that they are of crystal nature (Fig. 1). A surprising result about the ball-milled nanoparticles is the absence of lattice defects that one might expect from the balling process (as is the case in our ball-milled submicron particles (Fig. 1)).
The powder x-ray diffraction experiments were carried out at SPring-8 BL02B2 using the large Debye-Scherrer camera with an imaging plate. XRD data were collected various temperatures from 300 K to 20 K with a 0.01˚ step from 0.00˚ to 75.00˚ in 2θ. The wavelength of the incident x-ray was tuned to approximately 0.5Å using the Si double monochromator.
The lattice constants of the nanocrystals at various temperatures were analyzed by the Rietveld method. Nanoparticle CuO has the crystal structure as single crystal CuO as shown in Fig. 2. We found a large NTE effect (β=--1.06 10-4K-1) for 5nm nano crystals of CuO below its magnetic ordering temperature (Fig. 3). By comparison the renowned NTE compound ZrW2O8 has β=--2.6 10-5K-1 (1). Similar result was observed for nano particles of MnF2 but not for NiO. Larger particles of CuO and MnF2 also show prominent Invar effect below their magnetic ordering temperature constant, whereas this behaviour is not observed in NiO. We propose that the NTE 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, i.e., the magnetostriction.
Fig. 1 The electron micrograph of the nanocrystals (the left) and submicron particles of ball-milled CuO.
Fig. 2 The crystal structure of CuO. The arrows represent the ordered spins below its magnetic transition temperature.
Fig. 3 Negative thermal expansion in nanocrystals of CuO and MnF2, but not NiO. The unit cell volumes are unified by their room-temperature values, respectively.
As is highlighted by Andrew L. Goodwin in Nature Nanotechnology (6), “if the link between magnetostriction and the NTE in nanoparticles proves to be general – and the materials science community will no doubt explore this possibility – then these results really are a very significant advance. Nearly all high-end functional materials show some form of magnetic ordering – this includes high-temperature superconductors, colossal magnetoresistance manganites and the rapidly expanding family of multiferroics. These are precisely the type of materials used in multicomponent devices, where compatibility between mechanical properties is paramount”. Moreover, the present finding suggests that “the particle size affects their fundamental thermodynamics in nanocrystalline magnets. Particle size has always been an important variable in materials science, but now the field has a clear indication of how it might be used to vary – and even invert – the complex interdependencies among fundamental parameters such as temperature, pressure and magnetism. If these principles can be extended to multiferroic materials, where magnetic order and electric polarization are linked, one might hope to develop nanoscale switches and sensors with previously unimaginable electronic responses to changes in temperature or pressure.”
References
1. Mary, T.A., Evans, J.S.O., Vogt, T. & Sleight, A.W. Negative Thermal Expansion from 0.3 K to 1050 K in ZrW2O8. Science 272, 90-92 (1996).
2. Phillips, A.E., Goodwin, A.L., Halder, G.J., Southon, P.D. & Kepert, C.J. Nanoporosity and Exceptional Negative Thermal Expansion in Single-Network Cadmium Cyanide. Angew. Chem. Int. Ed 47, 1396-1399 (2008).
3. Goodwin A.L., et al. Colossal positive and negative thermal expansion in the framework material Ag3[Co(CN)6]. Science 319, 794-797 (2008).
4. X. G. Zheng , H. Kubozono, H. Yamada, K. Kato, Y. Ishiwata, C.N. Xu: Nature Nanotechnology 3 (2008) 724-726.
5. Zheng et al., Phys. Rev. Lett. 85 (2000) 5170-5173; J. Phys. Soc. Jpn. 70 (2001) 1054-1063; J. Appl. Phys. 92 (2002) 703-2708; Phys. Rev. B 69, 104104 (2004) 1-7.
6. Andrew L. Goodwin: Nature Nanotechnology 3 (2008) 711-712.英語フィールド
Author：X.G. ZhengTitle：
Giant negative thermal expansion in magnetic nanocrystalsAnnouncement information:SPring-8 Research Frontiers Vol: 2008An abstract：Giant negative thermal expansion in magnetic nanocrystalsAn abstract：Most solids expand when they are heated but a property known as negative thermal expansion (NTE) has been observed in a number of materials, including the oxide ZrW2O8 (1) and the framework material ZnxCd1-x(CN)2 (2). 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], has been explained in terms of the geometric flexibility of its metal-cyanide-metal linkages (3). 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 tunable positive or negative thermal expansion in industrial applications has led to intense interest in both the Invar effect and NTE.
Here we report our recent finding of giant negative thermal expansion in magnetic nanocrystals of CuO and MnF2 (4). The cupric oxide, CuO, is a unique transition metal mono oxide that was clarified by us to show strong charge-spin-lattice coupling and ferroelectric properties below its magnetic (antiferromagnetic) transition (5). This strong charge-spin-lattice coupling recently receives intense attention and is renamed by the term “multiferroics”. Our previous structure study suggested small anomalies in the lattice parameters at its magnetic transition temperatures (Néel temperature TN) and disappearance of thermal expansion below TN (i.e., zero thermal expansion). CuO fine particles with sizes narrowly distributed around ~5 nm were prepared by ball-milling from large (~cm) pure single crystals grown by a chemical vapour transport method. The high-resolution TEM image suggests that they are of crystal nature (Fig. 1). A surprising result about the ball-milled nanoparticles is the absence of lattice defects that one might expect from the balling process (as is the case in our ball-milled submicron particles (Fig. 1)).
The powder x-ray diffraction experiments were carried out at SPring-8 BL02B2 using the large Debye-Scherrer camera with an imaging plate. XRD data were collected various temperatures from 300 K to 20 K with a 0.01˚ step from 0.00˚ to 75.00˚ in 2θ. The wavelength of the incident x-ray was tuned to approximately 0.5Å using the Si double monochromator.
The lattice constants of the nanocrystals at various temperatures were analyzed by the Rietveld method. Nanoparticle CuO has the crystal structure as single crystal CuO as shown in Fig. 2. We found a large NTE effect (β=--1.06 10-4K-1) for 5nm nano crystals of CuO below its magnetic ordering temperature (Fig. 3). By comparison the renowned NTE compound ZrW2O8 has β=--2.6 10-5K-1 (1). Similar result was observed for nano particles of MnF2 but not for NiO. Larger particles of CuO and MnF2 also show prominent Invar effect below their magnetic ordering temperature constant, whereas this behaviour is not observed in NiO. We propose that the NTE 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, i.e., the magnetostriction.
Fig. 1 The electron micrograph of the nanocrystals (the left) and submicron particles of ball-milled CuO.
Fig. 2 The crystal structure of CuO. The arrows represent the ordered spins below its magnetic transition temperature.
Fig. 3 Negative thermal expansion in nanocrystals of CuO and MnF2, but not NiO. The unit cell volumes are unified by their room-temperature values, respectively.
As is highlighted by Andrew L. Goodwin in Nature Nanotechnology (6), “if the link between magnetostriction and the NTE in nanoparticles proves to be general – and the materials science community will no doubt explore this possibility – then these results really are a very significant advance. Nearly all high-end functional materials show some form of magnetic ordering – this includes high-temperature superconductors, colossal magnetoresistance manganites and the rapidly expanding family of multiferroics. These are precisely the type of materials used in multicomponent devices, where compatibility between mechanical properties is paramount”. Moreover, the present finding suggests that “the particle size affects their fundamental thermodynamics in nanocrystalline magnets. Particle size has always been an important variable in materials science, but now the field has a clear indication of how it might be used to vary – and even invert – the complex interdependencies among fundamental parameters such as temperature, pressure and magnetism. If these principles can be extended to multiferroic materials, where magnetic order and electric polarization are linked, one might hope to develop nanoscale switches and sensors with previously unimaginable electronic responses to changes in temperature or pressure.”
References
1. Mary, T.A., Evans, J.S.O., Vogt, T. & Sleight, A.W. Negative Thermal Expansion from 0.3 K to 1050 K in ZrW2O8. Science 272, 90-92 (1996).
2. Phillips, A.E., Goodwin, A.L., Halder, G.J., Southon, P.D. & Kepert, C.J. Nanoporosity and Exceptional Negative Thermal Expansion in Single-Network Cadmium Cyanide. Angew. Chem. Int. Ed 47, 1396-1399 (2008).
3. Goodwin A.L., et al. Colossal positive and negative thermal expansion in the framework material Ag3[Co(CN)6]. Science 319, 794-797 (2008).
4. X. G. Zheng , H. Kubozono, H. Yamada, K. Kato, Y. Ishiwata, C.N. Xu: Nature Nanotechnology 3 (2008) 724-726.
5. Zheng et al., Phys. Rev. Lett. 85 (2000) 5170-5173; J. Phys. Soc. Jpn. 70 (2001) 1054-1063; J. Appl. Phys. 92 (2002) 703-2708; Phys. Rev. B 69, 104104 (2004) 1-7.
6. Andrew L. Goodwin: Nature Nanotechnology 3 (2008) 711-712.