Evidence of reduced antiferromagnetic transition in mesocrystals of CuO synthesized by a surfactant-free solution phase method

Abstract

Electronic Supplementary Information (ESI) available: Evidence of morphological evolution of CuO ellipsoids from Cu(OH)2. XRD pattern and SEM images of samples taken at the intermediate stage of experiment is presented. Crystal structure of CuO is shown in S2. SeeWe explore the finite size effect on magnetic properties of CuO mesocrystals synthesized by a surfactant-free solution phase method. Significant evidence on the evolution of 3D oval, elliptical and 2D sheet-like CuO mesocrystals driven by oriented aggregation of CuO nano subunits is presented. Dimension of CuO nano-subunits constituting the mesocrystals as well as its final morphology is tailored by NaOH concentration in precursor solution. Changes in mesocrystal morphology reflect on the position and intensity of Raman vibrational modes. DC magnetization curves reveal distinct features of antiferromagnetic transitions where the magnetization behaviour of mesocrystal is influenced by the dimension of CuO nano subunits. The ordering temperature (TN) is reduced from bulk value of 230 K to 58 K as the size of CuO nano subunit decreases to 7 nm. Moreover, all nanostructures exhibit linear field dependent magnetization below the transition temperature similar to antiferromagnetic system. However, below TN field cooled isothermal magnetization display anomalous behaviour as a shift along the vertical axis whose origin is related to surface uncompensated spins. The vertical shift decreases as the CuO nano-subunit dimension increases.

Synthesis of Magnetite Nanorods from the Reduction of Iron Oxy-Hydroxide with Hydrazine

“…10,71 Small defects in stoichiometry and poor crystallinity would lead to the disappearance of Verwey transition. 1,71−73 saturation, 66,67 which is expected in typical antiferromagnetic materials. 43 Figure 10d shows hysteresis curves for Fe 3 O 4 nanorods at different temperatures (10, 150, and 300 K).…”

“… 10 , 71 Small defects in stoichiometry and poor crystallinity would lead to the disappearance of Verwey transition. 1 , 71 − 73 Figure 10 c represents the hysteresis curve of β-FeOOH nanorods which shows the linear dependence of magnetization ( M ) with the applied field without reaching saturation, 66 , 67 which is expected in typical antiferromagnetic materials. 43 …”

“… 63 − 65 A slight inflection point was observed at about 45 K on the FC curve (inset, Figure 10 a) which indicates the antiferromagnetic ordering temperature, T N . 66 − 68 The value of T N for β-FeOOH nanorods is lower than the bulk (270–299 K) and is usually attributed to the finite size and surface properties of materials. At the nanoscale, the size, shape, and synthetic procedure of nanomaterials can affect the ordering temperature.…”

“…The β-FeOOH nanoneedles are antiferromagnetic as demonstrated by the magnetic susceptibility (χ) versus temperature ( T ) curve typical of antiferromagnets shown in Figure a. A maximum blocking temperature of 14 K was observed in the ZFC curve. − A slight inflection point was observed at about 45 K on the FC curve (inset, Figure a) which indicates the antiferromagnetic ordering temperature, T N . − The value of T N for β-FeOOH nanorods is lower than the bulk (270–299 K) and is usually attributed to the finite size and surface properties of materials. At the nanoscale, the size, shape, and synthetic procedure of nanomaterials can affect the ordering temperature. , The ZFC magnetization versus temperature curve (Figure b) of Fe 3 O 4 shows a change in magnetization at 120 K, which is called a Verwey transition .…”

The Intriguing Nature of Fluorine Doping on Li2CuO2 and the Reasons Behind the Inhibition of Oxygen Evolution

“…Since there are no significant changes in the b cell parameter between the doped and nondoped material as demonstrated by XRD, these vibrational modes would not provide relevant information to demonstrate the effect of fluorine in the structure. Whereas, the B g2 modes offer much more information with regard to F doping, given that they are associated with perpendicular displacement on the b axis, which is due to oxygen–oxygen repulsion, and are strongly dependent on the polarization (Figure (b)). , So, changes in intensity or Raman shift on this vibrational mode can be associated with the partial replacement of oxygen sites by fluorine in the crystalline cell. The decrease of intensity of the B g2 band is evidenced through the intensity ratio between bands A g and B g2 , which is modified from 1.6 in Li 2 CuO 2 to 2.4 in the F-doped samples; this suggests that this decrease is due to the presence of fluorine, which decreases the repulsion between oxygen–oxygen on the c axis.…”