Surfactant-assisted production of TbCu2 nanoparticles

Abstract

The production of surfactant-assisted metallic nanoparticles of TbCu 2 has been achieved by the combination of high-energy ball milling in tungsten carbide containers and the use of oleic acid (C 18 H 34 O 2 ) and heptane (C 7 H 16 ). The alloys were first produced in bulk pellets by arc melting and subsequently milled for only 2 and 5 h in oleic acid (15 and 30% mass weight). The powders consist of an ensemble of nanoparticles with a TbCu 2 lattice cell volume of ≈215 Å 3 , an average particle diameter between 9 and 12 nm and inhomogeneous lattice strain of 0.2-0.4%, as deduced from X-ray diffraction data. The nanometric sizes of the crystals with defined lattice planes are close to those obtained by transmission electron microscopy. Raman spectroscopy shows the existence of inelastic peaks between 1000 and 1650 cm −1 , a characteristic of C 18 H 34 O 2 . The magnetisation shows a peak at the antiferromagneticparamagnetic transition with Néel temperatures around 48 K (below that of bulk alloy) and a distinctive metamagnetic transition at 5 K up to 40 K. The CurieWeiss behaviour above the transition reveals effective Bohr magneton numbers (≈9.1-9.9 μ B ) which are close to what is expected for the free Tb 3+ ion using Hund's rules. The metamagnetic transition is slightly augmented with respect to the bulk value, reaching H = 24.5 kOe by the combined effect of the size reduction and the lattice strain increase and the increase of magnetic disorder. At low temperatures, there is irreversibility as a result of the existing magnetic disorder. The moment relaxation follows an Arrhenius model with uncompensated Tb moments, with activation energies between 295 and 326 K and pre-exponential factors between 10 −11 and 10 −13 s. The results are interpreted as a consequence of the existence of a diamagnetic surfactant which drastically decreases the magnetic coupling between interparticle moments.

Investigating the Size and Microstrain Influence in the Magnetic Order/Disorder State of GdCu2 Nanoparticles

“…The dynamics of the magnetic moments nearby the freezing transition can be quantified by focusing on different critical exponents [ 21 , 22 , 46 ]. The obtained values for these are gathered in Table 4 .…”

“…On the other hand, the imaginary χ (T, f ) (see Figure 6b bottom for D ≈ 25 nm) follows the features of the real component [45]. The appearance of a second peak located around T ∼ 40 K may be connected to the existence of some FM interactions, as a pure AF alloy should not display a shoulder in The dynamics of the magnetic moments nearby the freezing transition can be quantified by focusing on different critical exponents [21,22,46]. The obtained values for these are gathered in Table 4.…”

“…In general, the literature is again very scarce for RCu intermetallic NPs [ 19 , 20 ]. A recent example is the work on TbCu NPs [ 21 , 22 ], as Tb -ions are the most similar to Gd -ones in terms of de Gennes factor and [ 15 ]. The aforementioned works have shown how the AF state survives within the mesoscopic scale together with the emergence of a disorder contribution in the form of a Spin Glass (SG) state, forming the so-called Superantiferromagnetic (SAF) state [ 23 ].…”

Oleogels Based on Palmitic Acid and Safflower Oil: Novel Formulations for Ocular Drug Delivery of Voriconazole

“…This observation can be correlated with the microscopic analysis, where it was found that there was a presence of plate‐like structures in PA40. Further, the average lattice strain values were found to be lowered as the concentration of the palmitic acid was increased . This observation was correct until the palmitic acid concentration was 35% w/w.…”

Using small-angle scattering to guide functional magnetic nanoparticle design

“…TbCu 2 (ref. 48) or GdCu 2 (ref. 49)) gained interest because their magnetic order can be easily tuned with particle size and microstrain.…”