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Bulk metallic glasses (BMGs) are thermodynamically metastable. As such, crystallization occurs when a BMG is thermally annealed at a temperature above the glass transition temperature. While extensive studies have been performed on the crystallization kinetics of BMGs, most of them have focused on the amorphous-to-crystalline structural ordering, and little attention has been paid to chemical distribution and its relationship with the structural ordering during the crystallization process. In this paper, a new approach, with simultaneous differential scanning calorimetry (DSC) and small angle neutron scattering (SANS) measurements, was applied to study in situ the crystallization of a Zr45.5Cu45.5Al9 BMG upon isothermal annealing at a temperature in the supercooled liquid region. Quantitative analysis of the DSC and SANS data showed that the structural evolution during isothermal annealing could be classified into three stages: (I) incubation; (II) amorphous-to-crystalline structural ordering; (III) continuous chemical redistribution. This finding was validated by composition analysis with atom probe tomography (APT), which further identified a transition region formed by expelling Al into the matrix. The transition region, with a composition of (Cu,Al)50Zr50, served as an intermediate step facilitating the formation of a thermodynamically stable crystalline phase with a composition of (Cu,Al)10Zr7.

Amorphous materials have no long-range order, but there are ordered structures at short range (2–5 A), medium range (5–20 A) and even longer length scales1–5. While regular6,7 and semiregular polyhedra8–10 are often found as short-range ordering in amorphous materials, the nature of medium-range order has remained elusive11–14. Consequently, it is difficult to determine whether there exists any structural link at medium range or longer length scales between the amorphous material and its crystalline counterparts. Moreover, an amorphous material often crystallizes into a phase of different composition15, with very different underlying structural building blocks, further compounding the issue. Here, we capture an intermediate crystalline cubic phase in a Pd-Ni-P amorphous alloy and reveal the structure of the medium-range order, a six-membered tricapped trigonal prism cluster (6M-TTP) with a length scale of 12.5 A. We find that the 6M-TTP can pack periodically to several tens of nanometres to form the cube phase. Our experimental observations provide evidence of a structural link between the amorphous and crystalline phases in a Pd-Ni-P alloy at the medium-range length scale and suggest that it is the connectivity of the 6M-TTP clusters that distinguishes the crystalline and amorphous phases. These findings will shed light on the structure of amorphous materials at extended length scales beyond that of short-range order. An intermediate cube phase with a medium-range order structure is identified in Pd-Ni-P metallic glass, which links the amorphous and crystalline phases.

The deformation behavior of CrMnFeCoNi high entropy alloy was investigated by in situ neutron diffraction at an ultralow temperature of 15 K. Analysis of the diffraction peak widths showed an extremely high dislocation density at 15 K, reaching ~1016 m−2. In addition, the dislocation density was found to closely follow the development of texture caused by deformation. In contrast to deformation by dislocation slip at room temperature, the ultralow-temperature deformation also involved stacking faults, twinning and serrations. The deformation pathway at ultralow temperature is outlined which is responsible for the extraordinary strength–ductility combination.

The multiscale structures in a Pd82Si18 binary bulk metallic glass before and after deformation were studied using electron microscopies, high-energy synchrotron X-ray diffraction, and small-angle scattering techniques. The experimental results revealed an enhancement of hierarchical structure heterogeneities on multiple length scales after deformation. Hierarchical multiple shear bands of high number density were observed after bending, introducing complex but periodically distributed residual strain. Pair distribution function analysis revealed that the connectivity of the short-range clusters on the medium-range scale determines the packing density difference between the tension side and the compression side in the sample after bending. In-situ synchrotron X-ray diffraction study also revealed a transformation of connection modes among short-range clusters under uniaxial tension and compression, which is consistent with those of triaxial tension/compression parts upon bending in Pd82Si18 glassy alloys. The nanoscale heterogeneities for metallic glasses after deformation observed by small-angle scattering and transmission electron microscopy may be attributed to the nanoscale amorphous phase separation and interacting multiple shear bands enhanced by plastic deformation. Our findings suggested that the enhancement of hierarchical heterogeneous structure on multiple length scales may explain the excellent plasticity of Pd-Si glassy alloys, deepening the understanding of structure-property relation during plastic deformation in metallic glasses.

In-situ synchrotron high-energy X-ray diffraction was used to study the kinetics of structure evolution for two Fe-based bulk metallic glasses with different thermophysical behaviors upon heating and isothermal annealing in the supercooled liquid region. It is found that the structure change of (Fe0.72B0.24Nb0.04)97Y3, an average glass former, follows a continuous disordering process before crystallization, while that of (Fe0.72B0.24Nb0.04)95.5Y4.5, a better glass former with an anomalous exothermic peak below the crystallization temperature, is characterized by a reentrant supercooled liquid behavior. A hidden amorphous phase with a configurationally highly-correlated structure is found at a critical temperature of the anomalous exothermic peak for the (Fe0.72B0.24Nb0.04)95.5Y4.5 supercooled liquid, and then it reenters the disordered phase of lower correlation length at a higher temperature. Synchrotron diffraction and the density measurements together illustrate that the liquid-liquid phase transition accompanies with an unusual density change upon isothermal annealing at the anomalous exothermic peak temperature. Our experimental results suggest that a liquid-liquid phase transition which occurred at the medium-range length scale plays an important role in stabilizing the (Fe0.72B0.24Nb0.04)95.5Y4.5 supercooled liquid. Possible mechanisms for the observed differences and the relationship with the glass-forming ability are discussed based on the results of the pair distribution function analysis.

A well-designed experimental method has been presented to in-situ visualize the amorphous-to-crystalline phase transformation of two glass formers at the atomic-length scale in the supercooled liquid region using a high voltage electron microscopy (HVEM). Analysis of the HVEM high-resolution images, supported by the in-situ synchrotron diffraction, further confirms previous observations of distinctively different crystallization pathways in the two Zr Cu Al alloys. Moreover, the HVEM results illustrate that isolated distributed nanocrystals with mutual orientation easily grew up from the Zr56Cu36Al8, an average glass former, which follows a classical crystallization pathway; while density population poorly ordered atomic clusters with large misorientation suspended the growth in the Zr46Cu46Al8, a good glass former, which might follow an unusual crystallization pathway. In addition, in-situ synchrotron diffraction measurements confirm that the Zr56Cu36Al8 alloy finally crystallized into an extended structure, in contrast, the final crystalline product of Zr46Cu46Al8 alloy possesses a damped structure. Our study provides a detailed microscopic understanding of the crystallization behaviors in the supercooled liquids, showing that the density population nucleation site with large misorientation and the confined final crystalline structure contribute to the stability of Zr Cu Al supercooled liquids.

Phase transformation is an effective means to increase the ductility of a material. However, even for a commonly observed face-centered-cubic to hexagonal-close-packed (fcc-to-hcp) phase transformation, the underlying mechanisms are far from being settled. In fact, different transformation pathways have been proposed, especially with regard to nucleation of the hcp phase at the nanoscale. In CrCoNi, a so-called medium-entropy alloy, an fcc-to-hcp phase transformation has long been anticipated. Here, we report an in situ loading study with neutron diffraction, which revealed a bulk fcc-to-hcp phase transformation in CrCoNi at 15 K under tensile loading. By correlating deformation characteristics of the fcc phase with the development of the hcp phase, it is shown that the nucleation of the hcp phase was triggered by intrinsic stacking faults. The confirmation of a bulk phase transformation adds to the myriads of deformation mechanisms available in CrCoNi, which together underpin the unusually large ductility at low temperatures.

Bulk metallic glasses (BMGs) are thermodynamically metastable. As such, crystallization occurs when a BMG is thermally annealed at a temperature above the glass transition temperature. While extensive studies have been performed on the crystallization kinetics of BMGs, most of them have focused on the amorphous-to-crystalline structural ordering, and little attention has been paid to chemical distribution and its relationship with the structural ordering during the crystallization process. In this paper, a new approach, with simultaneous differential scanning calorimetry (DSC) and small angle neutron scattering (SANS) measurements, was applied to study in situ the crystallization of a Zr45.5Cu45.5Al9 BMG upon isothermal annealing at a temperature in the supercooled liquid region. Quantitative analysis of the DSC and SANS data showed that the structural evolution during isothermal annealing could be classified into three stages: (I) incubation; (II) amorphous-to-crystalline structural ordering; (III) continuous chemical redistribution. This finding was validated by composition analysis with atom probe tomography (APT), which further identified a transition region formed by expelling Al into the matrix. The transition region, with a composition of (Cu,Al)50Zr50 , served as an intermediate step facilitating the formation of a thermodynamically stable crystalline phase with a composition of (Cu,Al)10Zr7 .

The multiscale structures in a Pd82Si18 binary bulk metallic glass before and after bending were studied using electron microscopy, high-energy synchrotron X-ray diffraction, and small-angle X-ray scattering. The experimental results revealed the enhancement of hierarchical structure heterogeneities on multiple length scales after deformation. Hierarchical multiple shear bands of high number density can be observed after bending, introducing complex but periodically distributed residual strain. Pair distribution function analysis revealed that the connectivity of the short-range cluster on the medium-range scale determines the packing density difference between the tension side and the compression side in the sample after bending. The electron density fluctuations on the nanoscale observed in the deformed part of the sample are indicative of a nanoscale amorphous phase separation induced by plastic deformation. Our findings will deepen the understanding of the plastic deformation mechanism of metallic glasses and shed light on designing glassy alloys of excellent plasticity and toughness through hierarchical multiscale structure heterogeneities.

Phase evolution of CoCrFeNiMo0.3 high entropy alloy (HEA) under different annealing temperatures was investigated by means of ultra-small-angle neutron scattering (USANS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). For the as-cast CoCrFeNiMo0.3 alloy, a dendritic structure consisting of mainly face-centered cubic (FCC) solid solution matrix and small amount of micro-sized σ precipitates was observed. Upon isothermal annealing, secondary phase precipitation occurred and precipitates with two size ranges (i.e., microscale and nanoscale) generated in the alloy. These precipitates were identified as newly formed μ and σ phases. Specifically, the size distribution of the nanoscale μ precipitates was determined by USANS measurements. It was found that the size of the nanoscale precipitates increased with the annealing temperature, jumping from 72 nm at 750 °C to 258 nm at 800 °C, which contributed to the sharp drop in hardness of the alloy. The present alloy maintained high hardness within a wide temperature range of 550–750 °C, which makes it a promising material for structural applications at intermediate temperatures.

Crystallization of Zr-Cu-Al-Ag bulk metallic glasses containing quenched-in crystals was studied by time-resolved in-situ neutron diffraction during isothermal annealing in the supercooled liquid region. The quenched-in crystals grew slowly at the beginning, indicating good thermal stability of the Zr-Cu-Al-Ag metallic glass alloys. The neutron diffraction results demonstrated that crystallization in Zr-Cu-Al-Ag metallic glasses was triggered by quenched-in crystals, rather than traditional heterogeneous nucleation mechanisms such as atomic-level impurities, container wall or surface oxides.

Crystallization kinetics of a series of Zr-Cu-Al bulk metallic glasses with different glass-forming abilities were systematically investigated using differential scanning calorimetry, time-resolved neutron diffraction, and high-resolution transmission electron microscopy. Experimental results revealed a transition of classic-to-avalanche types of nucleation for the Zr-Cu-Al glass alloys upon isothermal annealing. The classic mode is characterized by a continuous nucleation and growth of Zr2Cu-type crystals. The avalanche mode features an abrupt formation of massive Cu10Zr7-type precipitates with a complex, low-symmetry crystalline structure. Calorimetric measurements identified an anomalous exothermic peak prior to crystallization for metallic glasses with the Cu10Zr7-type crystalline phase. The formation of a metastable amorphous/semi-crystalline phase was observed using the electron microscopy prior to crystallization for glasses with an anomalous exothermic event. Our results indicate that the formation of a metastable phase might lower the free energy barrier of the crystallization and trigger an avalanche type of nucleation. Neutron diffraction pair distribution function analysis suggests that the easy connection of short-range clusters at the medium-range length scale would favor the avalanche nucleation.

In situ neutron diffraction measurement was applied to study the low-cycle fatigue behavior of CrFeCoNiMo0.2 high entropy alloy. A two-step stress-controlled fatigue test with a stress range of 100–460 and 20–500 MPa was employed. The as-cast sample was cycled 129,000 and 61,000 times, respectively, before fracture. The evolution of the lattice strain and peak intensity demonstrates that the main deformation mechanism is dislocation slip, while no evidence of stacking fault was found. A three-stage ratcheting was clearly observed. Under the stress-controlled mode, the experimentally determined dislocation density increases linearly with the ratcheting strain. The increase of the dislocation density results in a decay of the ratcheting strain rate, which stabilizes the structure and is beneficial for fatigue resistance.

We studied the deformation behavior of CrFeCoNi high-entropy alloy by in situ neutron diffraction at room temperature, intermediate low temperature of 140 K, low temperatures of 40 K (no serrated deformation) and 25 K (with massive serrations). The evolution of lattice strain and texture along different grain orientations provided distinct insights into deformation behavior at low temperatures. The in situ data showed an early activation of stacking faults and a higher stacking fault probability with decreasing test temperature. The stacking fault probability reached ∼4.7% at low temperatures. The dislocation density at 40 and 25 K evolved similarly and had a very high value of ∼9.2 × 1015 m−2. However, twin fault probability at 25 K (∼6%) was higher than that at 40 K (∼5%). The samples at 40 and 25 K deformed uniformly and lacked any necking region, thus imparting an excellent ductility of ∼58%. The contributions from different deformation mechanisms to the yield strength and strain hardening have been estimated. The athermal contributions to the yield strength were ∼183 MPa at all temperatures, while the Peierls stress increased significantly at low temperatures (from 148 MPa at room temperature to 493 MPa at 25 K). Dislocations contributed to ∼94% strain hardening at room temperature. Although the dislocation strengthening remained the major hardening mechanism at very low temperatures, the planar faults contribution increased steadily from 6% at room temperature to 28% at 25 K.

Deterioration of traditional mechanical expansion joints significantly affects the durability of bridge structures. Engineered cementitious composites have been proposed as an alternative to expansion joints in bridge decks. ECC link slabs were cast and tested under monotonic cyclic loading. Link slabs, reinforced with fibre-reinforced polymer bars, demonstrated sufficient flexibility to meet the current design protocols. Nonlinear finite element models were constructed based on the experimental data. Depth-span ratio and reinforcement ratio of such link slabs must not exceed 0.12 and 0.72%. Link slab debonded length should be larger than 0.8% to obtain low bending stiffness.

We investigated the in situ deformation behavior of the CrCoNi medium-entropy alloy at a cryogenic temperature of 140 K and compared it with deformation at room temperature. The sample exhibited higher strength and larger ductility at the cryogenic temperature. The CrCoNi alloy remained single-phase face-centered cubic at room temperature, while deformation at 140 K resulted in a martensitic transformation to the hexagonal close-packed structure. The phase transformation, an additional deformation mechanism to stacking faults, twinning, and dislocation slip, resulted in a higher work hardening at cryogenic temperature. The study addresses the structure metastability in the CrCoNi alloy, which led to the formation of epsilon-martensite from the intrinsic stacking faults.

Polyamorphic transition is the transition between two amorphous states or two liquid states (LLT) at a fixed composition of a substance. Experience in LLT is limited. Besides, its nature remains largely unknown as it occurs under the experimental conditions of high pressure/temperature (P/T) or high undercooling. In this study, we found that some undercooled Pd Ni P melts undergo a LLT. Contrary to all earlier studies, Pd Ni P specimens that contain the structural changes that occur at different stages of the LLT can be prepared for electron microscopy. HRTEM (high resolution transmission electron microscope) establishes that it is a first-order phase transition. From thermodynamics, a first-order phase change is accompanied by a latent heat. Here it was measured by a DSC (differential scanning calorimeter). A first-order LLT has important thermodynamic implications. First, it reconfirms that a liquid has different kinds of short-range-orders (SROs). Second, the first-order LLT implies that the SROs of a liquid are divided into distinct groups, each containing either a SRO or a number of different SROs, but not all. Physically, each group represents a real liquid. Third, the SRO(s) in a group can be assigned an independent Gibbs free energy, G SRO (P, T, c = composition) and the thermodynamics of the liquids can be described in terms of these G SRO .

Thermal behaviors and structures of three Zr-based binary glass formers, Zr 50 Cu 50 , Zr 64 Cu 36 and Zr 64 Ni 36 , were investigated and compared using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), high energy X-ray diffraction (XRD) and small angle X-ray scattering (SAXS). The high energy XRD results show that the bulk glass former Zr 50 Cu 50 has a denser atomic packing efficiency and reduced medium-range order than those of marginal glass formers Zr 64 Cu 36 and Zr 64 Ni 36 . Based on TEM observations for the samples after heat treatment at 10 K above their crystallization onset temperatures, the number density of crystals for Zr 50 Cu 50 was estimated to be 10 23 –10 24 m −3 , which was four-orders higher than that in Zr 64 Cu 36 and Zr 64 Ni 36 metallic glasses. SAXS results indicate that Zr 50 Cu 50 has higher degree of nanoscale inhomogeneities than those in Zr 64 Cu 36 and Zr 64 Ni 36 at as-cast state. The observed multiscale structures are discussed in terms of the phase stability and glass-forming ability of Zr-based binary glass formers.

In situ neutron diffraction revealed a unique deformation pathway in high-entropy alloys with unusually large ductility at 15 K., High-entropy alloys exhibit exceptional mechanical properties at cryogenic temperatures, due to the activation of twinning in addition to dislocation slip. The coexistence of multiple deformation pathways raises an important question regarding how individual deformation mechanisms compete or synergize during plastic deformation. Using in situ neutron diffraction, we demonstrate the interaction of a rich variety of deformation mechanisms in high-entropy alloys at 15 K, which began with dislocation slip, followed by stacking faults and twinning, before transitioning to inhomogeneous deformation by serrations. Quantitative analysis showed that the cooperation of these different deformation mechanisms led to extreme work hardening. The low stacking fault energy plus the stable face-centered cubic structure at ultralow temperatures, enabled by the high-entropy alloying, played a pivotal role bridging dislocation slip and serration. Insights from the in situ experiments point to the role of entropy in the design of structural materials with superior properties.

The presence of a liquid–liquid phase transition in the supercooled-liquid temperature range for a glass-forming Zr–Cu–Al–Ag alloy has been revealed using a suite of in situ neutron scattering techniques, including small-angle neutron scattering (SANS) and total neutron scattering. The SANS data analysis is indicative of the enhancement of nanoscale structural heterogeneities prior to crystallization, which is further supported by the total scattering result that points to an increase in the degree of medium-range ordering during the transition. In addition, a calorimetric anomaly and abnormal thermal expansion behavior were also observed upon heating. As such, this study provides multiscale structural evidence on the liquid–liquid phase transition and helps to gain insight into its underlying mechanism in terms of cluster connectivity.

In the present work, the microstructure evolution and macro-response of a ferromagnetic shape memory alloy under stimuli of magnetic fields with different frequency and coupled magnetic-mechanical loading are investigated via a real-space phase field simulation. It is found that the coercive field is reduced from 0.724 to 0.423 with the magnetic frequency f decrease from 2.5 × 10 − 5 Hz to 0.833 × 10 − 5 Hz, wherein the concomitant domain wall motion and magnetization rotation are captured as well. Moreover, simulation results demonstrate that, under the coupled magnetic-mechanical loading, the coercive field of the magnetic hysteresis loop could be reduced by applying a compressive strain perpendicular to the magnetic field direction. The domain evolution is mainly divided into three types during the coupled magnetic-mechanical loading, namely (a) domain wall motion with the magnetization rotation, (b) pure magnetization rotation, and (c) 180° domain coordinated domain switching. To better understand the domain evolution, we propose an index S = m 1 avg + m 2 avg , with m 1 avg and m 2 avg indicating the absolute value of the averaged magnetization component m 1 and m 2 over the whole studied system, to characterize the magnetization change during the microstructure evolution.

Despite having a negative heat of mixing, a metastable liquid/amorphous miscibility gap (MLMG) was found below the liquidus of the alloy system, Pd–Ni–P. Earlier, a direct determination of the complete MLMG was not possible because it lies in the undercooling regime. It is known that the morphology of an alloy system that has undergone a spinodal mechanism is interconnected. In this work, a morphological transition, from eutectic to interconnectedness, was used to determine the complete MLMG of the alloy system, Pd–Ni–P.

In the comments on “Structure origin of a transition of classic-to-avalanche nucleation in Zr-Cu-Al bulk metallic glasses, Acta Materialia, 149, 108 (2018)”, Altounian et al. argued that the avalanche type of nucleation observed in our paper is due to the presence of oxygen and other impurities. In this letter, we show that the amount of oxygen in our bulk metallic glass samples is far below the level found in ribbon samples that would trigger an explosive nucleation event. Rather, the avalanche type of nucleation reported in our study of Zr-Cu-Al bulk metallic glass is a compositional effect, where the elemental compositions were systematically varied leading to different crystalline phases.

Recently, it was found that undercooled molten Pd–Ni–P undergoes amorphous/liquid spinodal decomposition or equivalently the alloy system has a metastable liquid miscibility gap (MLMG) in its undercooling regime. This is unusual because the alloy system has a negative heat of mixing. In this work, a portion of the MLMG was determined, at 613 and 593 K. The incomplete MLMG obtained differs fundamentally from that of an alloy system with a positive heat of mixing. EDX and X-ray studies show that the MLMG is due to two unique short-range orders.

Pd41.25Ni41.25P17.5 bulk metallic glasses (BMGs) undergo phase separation despite the fact that the alloy system has a negative heat of mixing. By employing the techniques of small angle X-ray scattering (SAXS), it was found that the phase separation is consistent with a spinodal mechanism. Its occurrence is attributed to unique short-range orders in the amorphous (or liquid) state of the BMGs. (C) 2013 Elsevier B.V. All rights reserved.

Phase-separated Pd41.25Ni41.25P17.5 bulk metallic glasses (BMGs) were subjected to isothermal annealing at 613 K (340 °C) for different time periods, t, in the range of 0 ≤ t ≤ 8 hours. For 0 ≤ t ≲ 5 hours, crystalline precipitates, in the shape of spheres, appear and its density is more or less a linear function of t. They are randomly distributed in the amorphous matrix. For t ≳ 5 to 6 hours, the number density of the spherical crystalline precipitates increases rapidly. In addition, they are no longer distributed randomly in the phase-separated amorphous matrix. Clustering is displayed. Experimental results suggest that the clustering is due to cubic crystalline precipitates that start to appear when t ≈ 5 to 6 hours.

Earlier, it was shown that molten Pd 41.25 Ni 41.25 P 17.5 alloys can be cast into BMGs (bulk metallic glasses) of different microstructures, which are: (i) homogeneous BMGs (A-type), (ii) homogeneous BMGs embedded with crystalline precipitates (B-type), and (iii) phase-separated BMGs (C-type). Their crystallization behaviors were studied in this paper. At low annealing temperatures, the crystallization is characterized by spherical precipitates, each of which consists of a nanocrystalline core and a eutectic crust. The cores of the three types of BMGs are not of the same composition. At high annealing temperatures, there are cubic precipitates in addition to the spherical precipitates. For reference purposes, the crystallization of amorphous Pd 40 Ni 40 P 20 , a widely studied BMG, was examined. It was found that spherical precipitates, with a core composition different from those of Pd 41.25 Ni 41.25 P 17.5 BMGs, appear, but cubic precipitates are absent.

A universal strategy was developed for the preparation of high-temperature-stable carbon nanotube (CNT) -supported metal nanocatalysts by encapsulation with a mesoporous silica coating. Specifically, we first showed the design of one novel catalyst, Pt(@)CNT/SiO(2), with a controllable mesoporous silica coating in the range 11-39 nm containing pores ≈3 nm in diameter. The hollow porous silica shell offers a physical barrier to separate Pt nanoparticles from contact with each other, and at the same time the access of reactant species to Pt was not much affected. As a result, the catalyst showed high thermal stability against metal particle agglomeration or sintering even after being subjected to harsh treatments up to 500 °C. In addition, degradation in catalytic activity was minimized for the hydrogenation of nitrobenzene over the catalyst treated at 300 °C for 2 h. The scheme was also extended to coat porous silica onto the surfaces of CuRu(@)CNT and the resultant catalyst thereby can be reusable at least four times without loss of activity for the hydrogenolysis of glycerol. These results suggest that the as-prepared nanostructured CNT-supported catalysts may find promising applications, especially in those processes requiring rigorous conditions.

Silica microspheres were coated with Fe3O4 and carbon by the decomposition of ferrocene in an acetone system containing hydrogen peroxide. The system was heated at the temperature of 100 °C for the first 24 h and then 180 °C for the next 24 h. The as-prepared superparamagnetic colloids of SiO2@Fe3O4@C were dispersed in acetone and efficiently self-assembled into centimetre-sized 3D magnetic colloidal crystals under the induction of a 0.2 T magnetic field. Both optical microscope image and reflection spectrum show a blue color of the colloidal crystals, demonstrating photonic crystal features. Because of the thinness of the shell and the large difference in reflective index between the core and shell, a new pseudogap whose reflection cannot be predicted by Bragg's law was generated.