Effect of Pressure on Magnetic Properties of TM₃[Cr(CN)₆]₂·nH₂O Nanoparticles

Abstract

Effect of pressure on magnetic properties of magnetic nanoparticles, based on Prussian blue analogues, were studied in pressures up to 1.2 GPa. The Mn 3 [Cr(CN) 6 ] 2 · nH 2 O and Ni 3 [Cr(CN) 6 ] 2 · nH 2 O nanoparticles were prepared by reverse micelle technique. Transmission electron microscopy images show nanoparticles with average diameter of about 3.5 nm embedded in an organic matrix. The characteristic X-ray peaks of nanoparticles are more diffused and broader. Systems of nanoparticles behave as systems of interacting magnetic particles. The Curie temperature TC is reduced from T C = 56 K for Ni-Prussian blue analogues to T C = 21 K for Ni-nanoparticles system and from TC = 65 K for Mn-Prussian blue analogues to T C = 38 K for Mn-nanoparticles system. One can explain this reduction of the Curie temperature and of the saturated magnetization µs by dispersion of nanoparticles in an organic matrix i.e. by a dilution effect. Applied pressure leads to a remarkable increase in T C for system of Mn-nanoparticles (∆T C /∆p = +13 K/GPa) and to only slight decrease in T C for system of Ni-nanoparticles (∆T C /∆p = −3 K/GPa). The pressure effect follows behavior of the mother Prussian blue analogues under pressure. The increase in saturated magnetization, attributed to compression of the organic matrix, is very small.

High-pressure neutron scattering of the magnetoelastic Ni-Cr Prussian blue analog

“…44 Notably, nanoparticles of NiCrPB showed slightly different response to pressure than the "bulk" material, but a surfactant was used that might modify the surface anisotropy as well as the effective mulk modulus. 45 Using our model of NiCrPB, each system must be approached individually to properly identify the magnetic ground state of the constituent particles even though the coordination polymer repeat unit might be identical.…”

The Effect of Pressure on Magnetic Properties of Prussian Blue Analogues

“…This simple model mentioned above has already been tested on the TM 2+ 3 [Cr III (CN) 6 ] 2 •zH 2 O and KM 2+ [Cr(CN) 6 ] systems, where TM 2+ = Cr 2+ , Mn 2+ , Ni 2+ , Co 2+ , and M 2+ = Mn 2+ , Ni 2+ [29][30][31][32][33][34][35][36][37][38][39][40]. Our paper is focused on the pressure effect on crystal structure and magnetic properties.…”

“…The above-mentioned magnetic model was tested on the TM +2 3[Cr III (CN)6]2•zH2O system [29][30][31][32][33][34][35][36][37][38] and KTM 2+ Cr(CN)6 [39,40], where TM 2+ is a 3d ion and the following papers [29,32,34,[38][39][40] are focused on the pressure effect on magnetic properties of these two types of PBs. The Cr III in the low spin anion [Cr III (CN)6] 3− has (t2g) 3 orbital resulting in six ferromagnetic (FM) and nine antiferromagnetic (AFM) pathways, with (t2g) 3 (eg) 2 orbitals of Mn 2+ leading to JAF interaction.…”

“…Later in works [58] and [59], authors referred to preparation of cyanide bridged Cr III -Ni 2+ nanoparticles. The reverse micelle technique described in [56] was used [37,38]. The content of organic surfactants in the samples was estimated to about 22 wt.% Ni-NAP and 28 wt.% Mn-NAP.…”

“…We expect that pressure affects inter-NAP distance (high compressibility of an organic matrix) and changes magnetic properties of NAP. The applied pressure strengthens the magnetic super-exchange interaction of Mn-NAP with the increased overlapping of magnetic orbitals [38]. As it is shown in Figure 19b, pressure decreases T C (dT C = dp = −3 K/GPa) for the system of Ni-NAP with dominant JF, which is mainly attributed to less effective magnetic coupling due to the reduction in the bonding angle Ni 2+ -N≡C-Cr III from an ideal value of 180 • .…”