摘要
新型纳米结构如中空纳米颗粒和核壳纳米颗粒,因其独特的化学和物理功能以及巨大的应用前景而倍受化学、物理学和材料学等领域的科学家所广泛关注。在目前所发现纳米磁现象的基础之上,通过设计和制备各种磁性新型纳米结构,并探索其可能具有的纳米磁效应与功能,将可能利用所发现的新纳米磁效应来进一步提高磁信息容量。本论文围绕镍基磷化物新型纳米结构的制备、组装和磁性质进行了以下几个方面的研究:
1.采用有机液相化学反应法,以乙酰丙酮镍为镍源和三苯基膦为磷源,利用纳米Kirkendall效应成功一步合成出Ni2P中空纳米颗粒。并发现:Ni2P中空纳米颗粒是通过前期形成的颗粒Ni与三苯基膦反应并沿纳米Kirkendall桥不断向外扩散而形成。而且改变三苯基膦的浓度获得了中空直径从5nm到60nm的中空纳米颗,证实了三苯基膦可以作为一种表面活性剂以及新的廉价的磷源,来调控和提高Ni2P中空纳米颗粒的中空尺寸。
2.利用三苯基膦表面磷化镍纳米颗粒的工艺成功地合成出Ni/Ni2P核壳纳米颗粒。并发现:通过反应时间可以调控核壳比例,随着磷化时间的延长,Ni2P壳逐渐增厚,而Ni核不断减小,最终转变成Ni2P纳米颗粒。并且,将调整核壳比例后的Ni/Ni2P核壳纳米颗粒于氩气中退火,可以利用Ni核与Ni2P壳的化合反应合成出新型镍磷化物Ni3P。
3.对所合成纳米颗粒的室温磁性和磁热稳定性进行了深入研究。并发现:Ni/Ni2P核壳纳米颗粒存在铁磁-超顺磁转变,而Ni2P纳米颗粒为顺磁性。随着Ni2P壳的引入,表面磁性质的改性更加显著。磁表面改性后,颗粒的磁表面各向异性增强了,以致尺寸减小的同时磁热稳定性还可以提高,使利用尺寸来进一步提高磁信息容量成为可能。
4.通过选用铁磁-超顺磁转变温度更高的Ni/Ni2P核壳纳米颗粒进行自组装形成致密块材,获得了直到室温的记忆效应。并发现:采用平均转变温度更高的分散纳米颗粒进行自组装可以获得更高的记忆温区,并且减小组装间距可以进一步提升记忆温区;同时,增加测量磁场将导致记忆温区不断向低温移动;另外,利用磁-温记忆效应,实现了基于温度的磁信息读写新方式,使利用温度来进一步提高磁信息读写容量成为可能。
Increasing attention had been paid to the new styles of nanoscale structures with various application in the field of chemistry, physics and material, due to the unique properties and considerable potencial of the hollow nanostructures and core-shell nanostructures. On the basis of current nanoscale magnetic phenomena, the design and preparation of various new-style magnetic nanostructures with potential new nanomagnetic effect and properties would make it possible to further improve the capacity of magnetic information. In this thesis, the synthesis, assembly, and magnetic properties of the nickel-based phosphide nanoparticles with hollow and core-shell nanostructures were investigated.
Ni2P hollow nanoparticles with tunable void sizes were obtained by one-pot synthetic technique using triphenylphosphine as a lower-price phosphorus source in a mild temperature organic solution. It was found that the Ni2P hollow nanoparticles were formed by the reaction of as-formed Ni nanoparticles with the surface triphenylphosphine and the outward-diffusion of Ni core via Kirkendall bridges. Varied triphenylphosphine concentrations were used to prepare nanoparticles with void sizes tunable from about 5 to 60 nm in diameter, showing that the lower-price phosphorus source triphenylphosphine can serve a reactive surfactant to tune and heighten the void capacity for potentia applications.
Ni/Ni2P core-shell nanoparticles with tunable core-shell sizes were synthesized through surface phosphatizing Ni nanoparticles using triphenylphosphine as phosphorus source in a mild temperature organic solution. It was found that increasing phosphatizing time would lead to thickening of the Ni2P shell, with the Ni core diminishing. Overphosphatizing the particles would make Ni2P nanoparticles form with almost no Ni remaining. And after adjusting the core-shell proportion by reaction time, annealing the Ni/Ni2P core-shell nanoparticles would lead the formation of new-style phosphide Ni3P, through the chemical combination of Ni2P shell with inner Ni during annealing.
The magnetic properties of as-synthesized nickel-based phosphide nanoparticles were studied at and below the room temperature. It was found that the Ni/Ni2P core-shell nanoparticles have a magnetic transforming from ferromagnetism to superparamagnetism as warming from 10 K to the room temperature. However, the Ni2P nanoparticles are paramagnetic. As a result, the surface magnetic modification of Ni core by the Ni2P shell was enhanced as the increase of phosphatizing time. And the magnetic thermal stability of the nanoparticles with redued ferromagnetic Ni core was inproved through the enhanced influence of magnetic surface anisotropy after surface magnetic modification, which makes it possible to further improve the information capacity via size.
The magnetization-temperature memory effect up to room-temperature was observed in the self-assembly of Ni/Ni2P core-shell nanomagnetic particles under low-filed direct-current magnetization process. It was found that the self-assembly of nanoparticels with higher magnetic thermal stability can highen the temperature-rang for memory effect, and lowering interparticle spacing can further improve the temperature-rang. However, heightening applied magnetic field can suppress the memory effect with decreasing temperature-range. Moreover, a new mode to read-write magnetic coding was realized based on temperature using the memory effect, indicating a new way to further heighten the information capacity via temperature.
引文
[1]Song Q, Zhang Z J, Shape Control and Associated Magnetic Properties of Spinel Cobalt Ferrite Nanocrystals. J. Am. Chem. Soc.2004,126:6164-6168.
[2]Black C T, Murray C B, Sandstrom R L, et al. Spin-dependent tunneling in self-assembled cobalt-nanocrystal superlattices. Science,2000,290:1131-1134;
[3]Shi W S, Zeng H, Sahoo Y, et al. A general approach to binary and ternary hybrid nanocrystals. Nano Letters,2006,6:875-881.
[4]Gruner M E, Entel P, Magnetic properties of nanostructured hollow microspheres. Journal of Magnetism and Magnetic Materials,2007,310:2453-2455.
[5]Inderhees S E, Borchers J A, Green K S, et al. Manipulating the magnetic structure of Co Core/CoO shell nanoparticles:implications for controlling the exchange bias. Phys. Rev. Lett.,2008,101:117202.
[6]Jun Y W, Seo J W, Cheon J, Nanoscaling laws of magnetic nanoparticles and their applicabilities in biomedical sciences. Acc. Chem. Res.,2008,41:179-189.
[7]Cheon J, Kang N J, Lee S M, et al. Shape evolution of singlecrystalline iron oxide nanocrystals. J. Am. Chem. Soc.,2004,126:1950-1951.
[8]Park J I, Kang N J, Jun Y, et al. Superlattice and magnetism directed by the size and shape of nanocrystals. ChemPhysChem,2002,3:543-547.
[9]Morales M P, Veintemillas-Verdaguer S, Montero M I, et al. Surface and internal spin canting in y-Fe2O3 nanoparticles. Chem. Mater.,1999,11:3058-3064.
[10]Chiang I C, Chen D H, Synthesis of monodisperse FeAu nanoparticles with tunable magnetic and optical properties. Adv. Funct. Mater.,2007,17:1311-1316.
[11]Qiu J M, Wang J P, Tuning the crystal structure and magnetic properties of FePt nanomagnets. Adv. Mater.,2007,19:1703-1706.
[12]Brown W F, Thermal fluctuations of a single-domain particle. Phys. Rev.,1963, 130:1677.
[13]Singh V, Seehra M S, Bonevich J, Nickel-silica nanocomposite:variation of the blocking temperature with magnetic field and measuring frequency. J. Appl. Phys., 2008,103:07D524.
[14]Victora R H, Predicted time dependence of the switching field for magnetic materials. Phys. Rev. Lett.,1989,63:457.
[15]Kechrakos D, Trohidou K N, Magnetic properties of self-assembled interacting nanoparticles. Appl. Phys. Lett.,2002,81:4574-4576.
[16]Dormann J L, Fiorani D, Yamani M E, Field dependence of the blocking temperature in the superparamagnetic model:H2/3 coincidence. Phys. Lett. A,1987, 120:95-99.
[17]Bae C J, Angappane S, Park J G, et al. Experimental studies of strong dipolar interparticle interaction in monodisperse Fe3O4 nanoparticles. Appl. Phys. Lett., 2007,91:102502.
[18]Frankamp B L, Boal A K, Tuominen M T, et al. Direct Control of the magnetic interaction between iron oxide nanoparticles through dendrimer-mediated self-assembly. J. Am. Chem. Soc.,2005,127:9731-9735.
[19]Zeng H, Li J, Liu J P, et al. Exchange-coupled nanocomposite magnets by nanoparticle self-assembly. Nature,2002,420:395-398.
[20]Zeng H, Li J, Wang Z L, et al. Bimagnetic core/shell FePt/Fe3O4 nanoparticles. Nano Letters,2004,4:187-190.
[21]Skumryev V, Stoyanov S, Zhang Y, et al. Beating the superparamagnetic limit with exchange bias. Nature,2003,423:850-853.
[22]Kang S S, Miao G X, Shi S, et al. Enhanced magnetic properties of self-assembled FePt nanoparticles with MnO Shell. J. Am. Chem. Soc.,2006,128:1042-1043.
[23]Johnston-Peck A C, Wang J W, Tracy J B, Synthesis and structural and magnetic characterization of Ni(core)/NiO(shell) nanoparticles. ACS Nano,2009,3: 1077-1084.
[24]Seshadri R, Masala O, Spinel ferrite/MnO core/shell nanoparticles:chemical synthesis of all-oxide exchange biased architectures. J. Am. Chem. Soc.,2005,127: 9354-9355.
[25]Salabas E L, Rumplecker A, Kleitz F et al. Exchange anisotropy in nanocasted Co3O4 nanowires. Nano Letters,2006,6:2977-2981.
[26]Benitez M J, Petracic O, Salabas E L, et al. Evidence for core-shell magnetic behavior in antiferromagnetic Co3O4 nanowires. Phys. Rev. Lett.,2008,101: 097206.
[27]Jagadeesan D, Mansoori U, Mandal P, et al. Hollow spheres to nanocups:tuning the morphology and magnetic properties of single-crystalline α-Fe2O3 nanostructures. Angew. Chem. Int. Ed.,2008,47:7685-7688.
[28]Neel L, Surface magnetic anisotropy and superlattice orientation. J. Phys. Radium, 1954,15:255.
[29]Labaye Y, Crisan O, Berger L, et al. Surface anisotropy in ferromagnetic nanoparticles. J. Appl. Phys.,2002,91:8715-8717.
[30]Salazar-Alvarez G, Qin J, Sepelak V, et al. Cubic versus spherical magnetic nanoparticles:the role of surface anisotropy. J. Am. Chem. Soc.,2008,130: 13234-13239.
[31]http://www.spmtips.com/library/data_storage.
[32]Sun Y, Salamon M B, Gamier K, et al. Memory effects in an interacting magnetic nanoparticle system. Phys. Rev. Lett.,2003,91:167206.
[33]Tsoi G M, Wenger L E, Senaratne U, et al. Memory effects in a superparamagnetic γ-Fe2O3 system. Phys. Rev. B,2005,72:014445.
[34]Wang W Z, Deng J J, Lu J, et al. Memory effect in a system of zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs. Appl. Phys. Lett.,2007,91:202503.
[35]Yang H T, Hasegawa D, Takahashi M, et al. Achieving a noninteracting magnetic nanoparticle system through direct control of interparticle spacing. Appl. Phys. Lett.,2009,94:013103.
[36]Kwon S G, Hyeon T, Colloidal chemical synthesis and formation kinetics of uniformly sized nanocrystals of metals, oxides, and chalcogenides. Acc. Chem. Res.,2008,41:1696-1709.
[37]Gao J, Gu H, Xu B, Multifunctional magnetic nanoparticles:design, synthesis, and biomedical applications. Acc. Chem. Res.,2009,42:1097-1107.
[38]Latham A H, Williams M E, Controlling transport and chemical functionality of magnetic nanoparticles. Acc. Chem. Res.,2008,41:411-420.
[39]Sun Y, Mayers B, Xia Y N, Metal nanostructures with hollow interiors. Adv. Mater.,2003,15:641-646.
[40]Tu K N, Gosele U, Hollow nanostructures based on the kirkendall effect:design and stability considerations. Appl. Phys. Lett.,2005,86:093111.
[41]Sun Z, Yang Z, Zhou J, A General approach to the synthesis of gold-metal sulfide core-shell and heterostructures. Angew. Chem. Int. Ed.2009,48:2881-2885.
[42]Herrmann I K, Grass R N, Mazunin D, Synthesis and covalent surface functionalization of nonoxidic iron core-shell nanomagnets. Chem. Mater.,2009, 21:3275-3281.
[43]Puntes V F, Krishnan K M, Alivisatos A P, et al. Colloidal nanocrystal shape and size control:the case of cobalt. Science,2001,291:2115-2117.
[44]Hou Y, Xu Z, Peng S, et al. A facile synthesis of SmCos magnets from core/shell Co/Sm2O3 nanoparticles. Adv. Mater.,2007,19:3349-3352.
[45]Park J, Kang E, Son S U, et al. Monodisperse nanoparticles of Ni and NiO: synthesis, characterization, self-assembled superlattices, and catalytic applications in the suzuki coupling reaction. Adv. Mater.,2005,17:429-434.
[46]Winnischofer H, Rocha T C, Nunes W C, et al. Chemical synthesis and structural characterization of highly disordered Ni colloidal nanoparticles. ACS Nano,2008, 2:1313-1319.
[47]Peng S, Chao W, Jin X, et al. Synthesis and stabilization of monodisperse Fe nanoparticles. J. Am. Chem. Soc.,2006,128:10676-10677.
[48]Sun S H, Zeng H, Robinson D B, et al. Monodisperse MFe2O4 (M= Fe, Co, Mn) nanoparticles. J. Am. Chem. Soc.,2004,126:273-279.
[49]Zeng H, Rice P M, Wang S X, et al. Shape-controlled synthesis and shape-induced texture of MnFe2O4 nanoparticles. J. Am. Chem. Soc.,2004,126:11458-11459.
[50]Yin M, O'Brien S, Synthesis of monodisperse nanocrystals of manganese oxides. J. Am. Chem. Soc.,2003,125:10180-10181.
[51]Seo W S, Shim J H, Oh S J, et al. Phase-and size-controlled synthesis of hexagonal and cubic CoO nanocrystals. J. Am. Chem. Soc.,2005,127:6188-6189.
[52]Lou X W, Archer L A, Yang Z, Hollow micro-/nanostructures:synthesis and applications. Adv. Mater.,2008,20:3987-4019.
[53]Lee J, Park J C, Song H, A nanoreactor framework of Au/SiO2 yolk/shell structure for catalytic reduction of p-nitrophenol. Adv. Mater.2008,20:1523-1528.
[54]Fan H J, Gosele U, Zacharias M, Formation of nanotubes and hollow nanoparticles based on kirkendall and diffusion processes:a review. Small,2007,3:1660-1671.
[55]Yin Y D, Rioux R M, Erdonmez C K, et al. Formation of hollow nanocrystals through the nanoscale kirkendall effect. Science,2004,304:711-714.
[56]Yin Y D, Erdonmez C K, Cabot A, et al. Colloidal synthesis of hollow cobalt sulfide nanocrystals. Adv. Funct. Mater.,2006,16:1389-1399.
[57]Peng S, Sun S H, Synthesis and characterization of monodisperse hollow Fe3O4 nanoparticles. Angew. Chem. Int. Ed.,2007,46:4155-4158.
[58]Zhou T, Lu M, Zhang Z, Synthesis and characterization of multifunctional FePt/ZnO core/shell nanoparticles. Adv. Mater.,2010,22:403-406.
[59]Chen D, Li J, Shi C S, et al. Properties of core-shell Ni-Au nanoparticles synthesized through a redox-transmetalation method in reverse microemulsion. Chem. Mater.,2007,19:3399-3405.
[60]Lee S, Lee N, Park J, et al. Ni/NiO core/shell nanoparticles for selective binding and magnetic separation of histidine-tagged proteins J. Am. Chem. Soc.,2006,128: 10658-10659.
[61]Johnston-Peck A C, Wang J, Tracy J B, Synthesis and structural and magnetic characterization of Ni(core)/NiO(shell) nanoparticles. ACS Nano,2009,3: 1077-1084.
[62]Zhou W, Zheng K, He L, et al. Ni/Ni3C core-shell nanochains and its magnetic properties:one-step synthesis at low temperature. Nano Lett.,2008,28:1147-115.
[63]Zeng J, Huang J, Lu W, et al. Necklace-like noble-metal hollow nanoparticle chains:synthesis and tunable optical properties. Adv. Mater.,2007,19:2172-2176.
[64]Gao J, Gu H, Xu B, Multifunctional magnetic nanoparticles:design, synthesis, and biomedical applications. Acc. Chem. Res.,2009,42:1097-1107.
[65]Gruner M E, Entel P, Magnetic properties of nanostructured hollow microspheres. Journal of Magnetism and Magnetic Materials,2007,310:2453-2455.
[66]Senevirathne K, Burns A W, Bussell M E, et al. Synthesis and characterization of discrete nickel phosphide nanoparticles:effect of surface ligation chemistry on catalytic hydrodesulfurization of thiophene. Adv. Funct. Mater.,2007,17: 3933-3941.
[67]Oyama S T, Novel catalysts for advanced hydroprocessing:transition metal phosphides. J. Catal.,2003,216:343-349.
[68]Panneerselvam A, Malik M A, Afzaal M, et al. The chemical vapor deposition of nickel phosphide or selenide thin films from a single precursor. J. Am. Chem. Soc., 2008,130,2420-2423.
[69]Lou X W, Archer L A, A general route to nonspherical anatase TiO2 hollow colloids and magnetic multifunctional particles. Adv. Mater.,2008,20:1853-1858.
[70]Zalich M A, Vadala M L, Riffle J S, et al. Structural and magnetic properties of cobalt nanoparticles encased in siliceous shells. Chem. Mater.,2007,19: 6597-6603
[71]Lee J, Park J C, Song H, A nanoreactor framework of Au/SiO2 yolk/shell structure for catalytic reduction of p-nitrophenol. Adv. Mater.,2008,20:1523-1528.
[72]Yin Y D, Rioux R M, Erdonmez C K, et al. Formation of hollow nanocrystals through the nanoscale kirkendall effect. Science,2004,304:711-714.
[73]Chiang R K, Chiang R T, Formation of hollow Ni2P nanoparticles based on the nanoscale kirkendall effect. Inorg. Chem.,2007,46:369-372.
[74]Henkes A E, Schaak R E, Trioctylphosphine:a general phosphorus source for the low-temperature conversion of metals into metal phosphides. Chem. Mater.,2007, 19:4234-4241
[75]Henkes A E, Vasquez Y, Schaak R E, et al. Converting metals into phosphides:a general strategy for the synthesis of metal phosphide nanocrystals. J. Am. Chem. Soc.,2007,129:1896-1899.
[76]Lee S, Lee N, Park J, et al. Ni/NiO core/shell nanoparticles for selective binding and magnetic separation of histidine-tagged proteins J. Am. Chem. Soc.,2006,128: 10658-10659.
[77]Xu X L, Asher S A, Synthesis and utilization of monodisperse hollow polymeric particles in photonic crystals. J. Am. Chem. Soc.,2004; 126:7940-7941.
[78]Zhang G, Wang W, Yu Q, Li X. et al. Facile one-pot synthesis of PbSe and NiSe2 Hollow spheres:kirkendall-effect-induced growth and related properties. Chem. Mater.2009; 21:969-974.
[79]Yin Y D, Erdonmez C K, Cabot A, et al. Colloidal synthesis of hollow cobalt sulfide nanocrystals. Adv. Funct. Mater.,2006,16:1389-1399.
[80]Park J, Kang E, Son S U, et al. Monodisperse nanoparticles of Ni and NiO: synthesis, characterization, self-assembled superlattices, and catalytic applications in the Suzuki coupling reaction. Adv. Mater.,2005,17:429-434.
[81]Ge J P, Zhang Q, Zhang T R, et al. Self-assembly and field-responsive optical diffractions of superparamagnetic colloids. Angew. Chem., Int. Ed.,2008,47: 8924-8926.
[82]Hou Y, Xu Z, Peng S, et al. A facile synthesis of SmCo5 magnets from core/shell Co/Sm2O3 nanoparticles. Adv. Mater.,2007,19:3349-3352.
[83]Zheng H, Wang J, Lofland S E, et al. Multiferroic BaTiO3-CoFe2O4 nanostructures. Science,2004,303:661-663.
[84]Thakar R, Chen Y C, Snee P T, et al. Efficient emission from core/(doped) shell nanoparticles:applications for chemical sensing. Nano Lett.,2007,7:3429.
[85]Chen W T, Yang T T, Hsu Y J, et al. Au-CdS core-shell nanocrystals with controllable shell thickness and photoinduced charge separation property. Chem. Mater.,2008,20:7204-7207.
[86]Kim H, Achermann M, Balet L P, et al. Synthesis and characterization of Co/CdSe core/shell nanocomposites:bifunctional magnetic-optical nanocrystals. J. Am. Chem. Soc.,2005,127:544-5446.
[87]Ma D L, Guan J W, Normandin F, et al. Multifunctional nano-architecture for biomedical applications. Chem. Mater.,2006,18,1920-1926.
[88]Senevirathne K, Burns A W, Bussell M E, et al. Synthesis and characterization of discrete nickel phosphide nanoparticles:effect of surface ligation chemistry on catalytic hydrodesulfurization of thiophene. Adv. Funct. Mater.,2007,17: 3933-3941.
[89]Oyama S T, Novel catalysts for advanced hydroprocessing:transition metal phosphides. J. Catal.,2003,216:343-349.
[90]Panneerselvam A, Malik M A, Afzaal M, et al. The chemical vapor deposition of nickel phosphide or selenide thin films from a single precursor. J. Am. Chem. Soc., 2008,130,2420-2423.
[91]Zalich M A, Vadala M L, Riffle J S, et al. Structural and magnetic properties of cobalt nanoparticles encased in siliceous shells. Chem. Mater.,2007,19: 6597-6603
[92]Xu Z C, Hou Y L, Sun S H, et al. Magnetic core/shell Fe3O4/Au and Fe3O4/Au/Ag nanoparticles with tunable plasmonic properties. J. Am. Chem. Soc.,2007,129: 8698-8699.
[93]Casavola M, Grillo V, Carlino E, et al. Topologically controlled growth of magnetic-metal-functionalized semiconductor oxide nanorods. Nano Lett.,2007,7: 1386-1392.
[94]Lee J S, Shevchenko E V, Talapin D V, et al. Au-PbS core-shell nanocrystals: plasmonic absorption enhancement and electrical doping via intra-particle charge transfer. J. Am. Chem. Soc.,2008,13:9673-9677.
[95]Chiang R K, Chiang R T, Formation of hollow Ni2P nanoparticles based on the nanoscale kirkendall effect. Inorg. Chem.,2007,46:369-372.
[96]Henkes A E, Schaak R E, Trioctylphosphine:a general phosphorus source for the low-temperature conversion of metals into metal phosphides. Chem. Mater.,2007, 19:4234-4241
[97]Henkes A E, Vasquez Y, Schaak R E, et al. Converting metals into phosphides:a general strategy for the synthesis of metal phosphide nanocrystals. J. Am. Chem. Soc.,2007,129:1896-1899.
[98]Pfeiffer H, Tancret F, Brousse T, et al. Synthesis, characterization and thermal stability of Ni3P coatings on nickel. Mater. Chem. Phys.,2005,92:534-539.
[99]Liu X G, Chen J X, Zhang J Y, et al. A novel catalyst for gas phase hydrodechlorination of chlorobenzene:Silica supported Ni3P. Catal. Commun., 2007,8:1905-1908.
[100]Hu X L, Yu J C, High-yield synthesis of nickel and nickel phosphide nano wires via microwave-assisted processes. Chem. Mater.,2008,20:6743-6747.
[101]Li J, Zeng H, Sun S, Analyzing the structure of CoFe-Fe3O4 Core-shell nanoparticles by electron imaging and diffraction. J. Phys. Chem. B,2004,108: 14005-14008.
[102]Kim J, Rong C B, Lee Y M, et al. From core/shell structured FePt/Fe3O4/MgO to ferromagnetic FePt nanoparticles. Chem. Mater.,2008,20:7242-7236.
[103]Zhang X B, Yan J M, Han S, et al. Magnetically recyclable Fe@Pt core-shell nanoparticles and their use as electrocatalysts for ammonia borane oxidation:the role of crystallinity of the core. J. Am. Chem. Soc.2009,131:2778-2781.
[104]Skumryev V, Stoyanov S, Zhang Y, et al. Beating the superparamagnetic limit with exchange bias. Nature,2003,423:850-853.
[105]Chiang I C, Chen D H, Synthesis of monodisperse FeAu nanoparticles with tunable magnetic and optical properties. Adv. Funct. Mater.,2007,17:1311-1316.
[106]Qiu J M, Wang J P, Tuning the crystal structure and magnetic properties of FePt nanomagnets. Adv. Mater.,2007,19:1703-1706.
[107]Zeng H, Li J, Wang Z L, et al. Bimagnetic core/shell FePt/Fe3O4 nanoparticles. Nano Letters,2004,4:187-190.
[108]Malozemoff A P, Random-field model of exchange anisotropy at rough ferromagnetic-antiferromagnetic interfaces. Phys. Rev. B,1987,35:3679-3682.
[109]Carey M J, Berkowitz A E, Exchange anisotropy in coupled films of Ni81Fe19 with NiO and CoxNi1-xO. Appl. Phys. Lett.,1992,60:3060-3062.
[110]Jungblut R, Coehoorn R, Johnson MT, et al. Orientational dependence of the exchange biasing in molecular-beam-epitaxy-grown Ni80Fe20/Fe50Mn50 bilayers. J. Appl. Phys.,1994,75:6659-6662.
[111]Sort J, Nogues J, Amils X, et al. Room-temperature coercivity enhancement in mechanically alloyed antiferromagnetic-ferromagnetic powders. Appl. Phys. Lett., 1999,75:3177-3179.
[112]Lin T, Mauri D, Stand N, et al. Improved exchange coupling between ferromagnetic Ni-Fe and antiferromagnetic Ni-Mn-based films. Appl. Phys. Lett., 1994,65:1183-1185.
[113]Moran T J, Gallego J M, Schuller I K, Increased exchange anisotropy due to disorder at permalloy/CoO interfaces. J. Appl. Phys.,1995,78:1887-1891.
[114]Nogues J, Ledennan D, Moran T J, et al. Large exchange bias and its connection to interface structure in FeF2-Fe bilayers. Appl. Phys. Lett.,1996,68:3186-3188.
[115]Zhou S M, Chien C L, Dependence of exchange coupling on magnetization in Co-Ni/FeMn bilayers. Phys. Rev. B,2001,63:104406-104409.
[116]Koon N C, Calculations of exchange bias in thin films with ferromagnetic/ antiferromagnetic interfaces. Phys. Rev. Lett.,1997,78:4865-4868.
[117]Yi J B, Ding J, Zhao Z L, et al. High coercivity and exchange coupling of Ni/NiO nanocomposite film, J. Appl. Phys.,2005,97:10K306.
[118]Kodama R H and Berkowitz A E. Surface spin disorder in NiFe2O4 nanoparticles. Phys. Rev. Lett.,1996,77:394-397.
[119]Y. Shi, J. Ding. Strong unidirectional anisotropy in mechanically alloyed spinel ferrites. J. Appl. Phys.,2001,90:4078-4084.
[120]Garaninl D A, Kachkachi H, Surface contribution to the anisotropy of magnetic nanoparticles. Phys. Rev. Lett.,2003,90:065504.
[121]Labaye Y, Crisan O, Berger L, et al. Surface anisotropy in ferromagnetic nanoparticles. J. Appl. Phys.,2002,91:8715.
[122]Garaninl D A, Kachkachi H, Surface contribution to the anisotropy of magnetic nanoparticles. Phys. Rev. Lett.,2003,90:065504.
[123]Junk I.H, Titus L, David S, et al. Enhancing exchange bias with diluted antiferromagnets. Phys. Rev. Lett.,2006,96:117204-117207.
[124]Berger L, Labaye Y, Tamine M, et al. Ferromagnetic nanoparticles with strong surface anisotropy:spin structures and magnetization processes. Phys. Rev. B, 2008,77:104431.
[125]Neel L, Surface magnetic anisotropy and superlattice orientation. J. Phys. Radium, 1954,15:255.
[126]Kodama R H, Salah A M, Berkowitz A E. Finite size effects in antiferromagnetic NiO nanoparticles, Phys. Rev. Lett.,1997,79:1393-1396.
[127]Biasi E D, Zysler R D, Ramos C A, et al. Surface anisotropy and surface-core interaction in Co-Ni-B and Fe-Ni-B dispersed amorphous nanoparticles. Phys. Rev. B,2005,71:104408.
[128]Yanes R, Chubykalo-Fesenko O, Kachkachi H, et al. Effective anisotropies and energy barriers of magnetic nanoparticles with Neel surface anisotropy. Phys. Rev. B,2007,76:064416.
[129]Gambardella P, Rusponi S, Veronese M, Giant magnetic anisotropy of single cobalt atoms and nanoparticles. Science,2003,300:1130-1132.
[130]Salazar-Alvarez G, Qin J, Sepelak V, et al. Cubic versus spherical magnetic nanoparticles:the role of surface anisotropy. J. Am. Chem. Soc.,2008,130: 13234-13239.
[131]Park H Y, Schadt M J, Wang L Y, et al. Fabrication of magnetic core@shell Fe oxide@Au nanoparticles for interfacial bioactivity and bio-separation. Langmuir, 2007,23:9050-9056.
[132]Bartel L C and Morosin B. Exchange striction in NiO. Phys. Rev. B,1971,3: 1039-1043.
[133]Gangopadhyay S, Hadjipanayis G. C, Sorensen C M, et al. Exchange anisotropy in oxide passivated Co fine particles. J. Appl. Phys.,1993,73:6964.
[134]Hayamizu S, Tabata H, Tanaka H, et al. Preparation of crystallized zinc oxide films on amorphous glass substrates by pulsed laser deposition. J. Appl. Phys., 1996,80:787-789
[135]Turgut Z, Nuhfer N T, Piehler H R, et al. Magnetic properties and microstructural observations of oxide coated FeCo nanocrystals before and after compaction. J. Appl. Phys.,1999,85:4406-4408.
[136]Matsumoto Y, Murakami M, Shono T, et al. Room-temperature ferromagnetism in transparent transition metal-doped titanium dioxide. Science,2001,291:854-856.
[137]Sun XC, Dong X L. Magnetic properties and microstructure of carbon encapsulated Ni nanoparticles and pure Ni nanoparticles coated with NiO layer. Mater. Res. Bull.,2002,37:991-1004.
[138]Sahoo S, Binek C, Kleemann W. Giant metamagnetic moments in a granular FeCl2-Fe heterostructure. Phys. Rev. B,2003,68:174431-174434.
[139]Wen G H, Zheng R K, Fung K K, et al. Microstructural and magnetic properties of passivated Co nanoparticle films. J. Magn. Magn. Mater.,2004,270:407-412.
[140]Li L P, Chen L J, Qihe R, et al. Magnetic crossover of NiO nanocrystals at room temperature. Appl. Phys. Lett.,2006,89:134102-134104.
[141]Liu C, Zou B S, Rondinone A J, et al. Chemical control of superparamagnetic properties of magnesium and cobalt spinel ferrite nanoparticles through atomic level magnetic couplings. J. Am. Chem. Soc.,2000,122:6263-6267.
[142]Frankamp B L, Boal A K, Tuominen M T, et al. Direct Control of the magnetic interaction between iron oxide nanoparticles through dendrimer-mediated self-assembly. J. Am. Chem. Soc.,2005,127:9731-9735.
[143]Brown W F, Thermal fluctuations of a single-domain particle. Phys. Rev.,1963, 130:1677.
[144]Neel L, Surface magnetic anisotropy and superlattice orientation. J. Phys. Radium, 1954,15:255.
[145]Yanes R, Chubykalo-Fesenko O, Kachkachi H, et al. Effective anisotropies and energy barriers of magnetic nanoparticles with Neel surface anisotropy. Phys. Rev. B,2007,76:064416.
[146]Usov N A, Grebenshchikov Y B, Influence of surface anisotropy on magnetization distribution in a single-domain particle. Journal of applied physics,2008,104: 043903.
[147]Meikejohn W H, Exchange anisotropy:a review. J. Appl. Phys.,1962,33: 1328-1335.
[148]Mauri D, Siegmann H, Bagus P, et al. Simple model for thin ferromagnetic films exchange coupled to an antiferromagnetic subst rate. J. Appl. Phys.,1987,62: 3047-3050.
[149]Malozemoff A P, Mechanisms of exchange anisot ropy. J. Appl. Phys.,1988,63: 3874-3879.
[150]Malozemff A P. Random-field model of exchange anisotropy at rough ferromagnetic-antiferromagnetic interfaces. Phys. Rev. B,1987,35:3679-3682.
[151]Soeya S, Fuyama M, Tadokoro S, et al. NiO structure-exchange anisotropy relation in the Ni81Fe19/NiO films and thermal stability of its NiO film. J. Appl. Phys.1996,79:1604-1610.
[152]Lederman D, Nogues J, Schuller I K, Exchange anisotropy and the antiferromagnetic surface order parameter. Phys. Rev. B,1997,56:2332-2335.
[153]Schulthess T, Butler W, Consequences of spin-flop coupling in exchange biased films. Phys. Rev. Lett.,1998,81:4516-4519.
[154]Bianco L D, Fiorani D, Testa A M, et al. Field-cooling dependence of exchange bias in a granular system of Fe nanoparticles embedded in an Fe oxide matrix. Phys. Rev. B,2004,70:052401-052404.
[155]Malozemff A P, Random-field model of exchange anisotropy at rough ferromagnetic-antiferromagnetic interfaces. Phys. Rev. B,1987,35:3679-3682.
[156]Vander Z P J, Ijiri Y, Borchers J A, et al. Difference between blocking and Neel temperatures in the exchange biased Fe3O4/CoO system. Phys. Rev. Lett.,2000,84: 6102-6105
[157]Cai J W, Liu K and Chien C L. Exchange coupling in the paramagnetic state. Phys. Rev. B,1999,60:72-75
[158]Kodama R H, Berkowitz A E. Atomic-scale magnetic modeling of oxide nanoparticles. Phys. Rev. B,1999,59:6321-6336.
[159]Gruyters M. Spin-glass-like behavior in CoO nanoparticles and the origin of exchange bias in layered CoO/Ferromagnet structures, Phys. Rev. Lett.,2005,95: 077204-077207.
[160]Fitzsimmons M R, Kirby B J, Roy S, et al. Pinned magnetization in the antiferromagnet and ferromagnet of an exchange bias system. Phys. Rev. B,2007, 75:214412-214421.
[161]Mannan A, Patrich A, Christopher H M, et al. Exchange bias using a spin glass. Nature Mater.,2007,6:70-75.
[162]Sun Y, Salamon M B, Gamier K, et al. Memory effects in an interacting magnetic nanoparticle system. Phys. Rev. Lett.,2003,91:167206.
[163]Zheng R K, Gu H W, Xu B, et al. Memory effects in a nanoparticle system: Low-field magnetization and ac susceptibility measurements. Phys. Rev. B,2005, 72:014446.
[164]Tsoi G M, Wenger L E, Senaratne U, et al. Memory effects in a superparamagnetic γ-Fe2O3 system. Phys. Rev. B,2005,72:014445.
[165]Wang W Z, Deng J J, Lu J, et al. Memory effect in a system of zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs. Appl. Phys. Lett.,2007,91:202503.
[166]Yang H T, Hasegawa D, Takahashi M, et al. Achieving a noninteracting magnetic nanoparticle system through direct control of interparticle spacing. Appl. Phys. Lett.,2009,94:013103.
[167]Chakraverty S, Ghosh B, Kumar S, et al. Magnetic coding in systems of nanomagnetic particles. Appl. Phys. Lett.,2006,88:42501-42503.
[168]Black C T, Murray C B, Sandstrom R L, et al. Spin-dependent tunneling in self-assembled cobalt-nanocrystal superlattices. Science,2000,290:1131.
[169]Jang S J, Kong W J, Zeng H, et al. Magnetotransport in Fe3O4 nanoparticle arrays dominated by noncollinear surface spins. Phys. Rev. B,2007,76:212403.
[170]Dai J B, Wang J Q, Sangregorio C, et al. Magnetic coupling induced increase in the blocking temperature of γ-Fe2O3 nanoparticles. J. Appl. Phys.,2000,87:7397.
[171]K. Nakata, Y. Hu, Uzun O, et al. Chains of superparamagnetic nanoparticles. Adv. Mater.,2008,20:4294-4299.
[172]Majetich S A, Jin Y, Magnetization directions of individual nanoparticles. Science, 1999,284:470-473.
[173]Bader S D, Colloquium:opportunities in nanomagnetism. Rev. Mod. Phys.,2006, 78:01-15.
[174]Brown W F, Thermal fluctuations of a single-domain particle. Phys. Rev.,1963, 130:1677.
[175]Usov N A, Grebenshchikov Y B, Influence of surface anisotropy on magnetization distribution in a single-domain particle. J. Appl. Phys.,2008,104:043903.
[176]Singh V, Seehra M S, Bonevich J, Nickel-silica nanocomposite:variation of the blocking temperature with magnetic field and measuring frequency. J. Appl. Phys., 2008,103:07D524.
[177]Victora R H, Predicted time dependence of the switching field for magnetic materials. Phys. Rev. Lett.,1989,63:457.
[178]Bae C J, Angappane S, Park J G, et al. Experimental studies of strong dipolar interparticle interaction in monodisperse Fe3O4 nanoparticles. Appl. Phys. Lett., 2007,91:102502.
[179]Frankamp B L, Boal A K, Tuominen M T, et al. Direct Control of the magnetic interaction between iron oxide nanoparticles through dendrimer-mediated self-assembly. J. Am. Chem. Soc.,2005,127:9731-9735.
[180]Nunes W C, Socolovsky L M, Denardin J C, et al. Role of magnetic interparticle coupling on the field dependence of the superparamagnetic relaxation time. Phys. Rev. B,2005,72:212413.
[181]Dormann J L, Fiorani D, Yamani M E, Field dependence of the blocking temperature in the superparamagnetic model:H2/3 coincidence. Phys. Lett. A,1987, 120:95-99.
[182]Kechrakos D, Trohidou K N, Magnetic properties of self-assembled interacting nanoparticles. Appl. Phys. Lett.,2002,81:4574-4576.