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. PACS numbers: 75.30.Cr, 75.50.Ee, 75.50.Gg, 75.50.Xx (489) 490 A. Zentko et al.

We report a study of magnetocaloric effect (MCE) in cyanido-bridged {[M(II)(pyrazole)(4)](2)[Nb(IV)(CN)(8)]·4H(2)O}(n) molecular compounds where M = Ni, Mn, pyrazole = C(3)H(4)N(2). The substances show a sharp phase transition to a long range magnetically ordered state, with ferromagnetic coupling between M and Nb sublattices in the case of the Ni-based sample 1 (T(c) = 13.4 K) and ferrimagnetic coupling for the Mn-based sample 2 (T(c) = 23.8 K). The magnetic entropy change ΔS due to applied field change ΔH as a function of temperature was determined by the magnetization and heat capacity measurements. The maximum value of ΔS at μ(0)ΔH = 5 T is 6.1 J mol(-1) K(-1) (5.9 J kg(-1) K(-1)) for 1 at T = 14 K and 6.7 J mol(-1) K(-1) (6.5 J kg(-1) K(-1)) for 2 at T = 25 K. MCE data at different applied fields have been presented as one universal curve, which confirms magnetic transitions in 1 and 2 to be of second order. The temperature dependences of the n exponent characterizing the dependence of ΔS on ΔH have been obtained. The n(T(c)) values, consistent with the shape of the magnetization curves, pointed to the 3D Heisenberg behaviour for 2 and some anisotropy, probably of the XY type, for 1. The (H/T(c))(2/3) dependence of the maximum entropy change has been tested in the ferrimagnetic Mn(2)-L-[Nb(CN)(8)] (L = C(3)H(4)N(2), C(4)H(4)N(2)) series.

A comprehensive study of the magnetocaloric effect (MCE) in the Mn 2 -[Nb(CN) 8 ] molecular magnet with a two-step magnetic sponge behavior is reported. The structural transformations provoked by dehydration bring about an increase in the magnetic ordering temperature (T c ) from 43 K through to 68 K and up to 98 K. All three phases are soft isotropic

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In the present study we report the structural and magnetic response of the 3-D cyano-bridged magnetic sponge-like system {[Mn II (pydz)(H 2 O) 2 ][Mn II (H 2 O) 2 ][Nb IV (CN) 8 ]?3H 2 O} n A to external pressure up to 1.8 GPa using single-crystal crystallography and magnetic measurements. The observed pressure-induced structural changes: shrinkage of the Nb-C bonds and bending of Mn-NC-Nb linkages are responsible for the strengthening of the antiferromagnetic interactions between Mn and Nb centers and consequently for the substantial increase of the magnetic ordering temperature from 43 K to 51 K under 0.57 GPa. The observed magneto-structural response to external pressure is similar in nature to the removal of guest molecules and confirms the significant susceptibility of molecular magnetic sponges to mechanical stress.

Magnetization measurements performed on Prussian blue analogs Mn, Fe, Co, Ni, Cu) confirmed the dual character of the exchange interaction (antiferromagnetic AFM and ferromagnetic FM) in this system. AFM interaction dominates for the Cr 2+ sample and with rising atomic number Z the FM interaction becomes more important reaching pure FM character for the Cu 2+ sample.

We present the study of pressure effect on magnetic properties of TM 2+ 3 [Cr III (CN) 6 ] 2 · nH 2 O ferrimagnets and ferromagnets (TM = Cr and Co) under pressures up to 0.9 GPa. Applied pressure strengthens super--exchange interaction in Cr 2+ -prussian blue analogues with dominant antiferromagnetic interaction JAF leading to increase in the Curie temperature TC (∆T c /∆p = 29.0 K/GPa) and reduces T C of Co 2+ -prussian blue analogues with dominant ferromagnetic interaction JF (∆Tc/∆p = −1.8 K/GPa). The rise of J AF interaction is attributed to the enhanced value of the single electron overlapping integral S. On the other hand, the applied pressure slightly affects bonding angles between magnetic ions mediated by the cyano-bridge and reduces the strength of magnetic coupling. Changes of the magnetization curve with pressure can be attributed to changes of magnetic anisotropy. The reduction of magnetization with pressure observed on Cr 2+ -prussian blue analogues can be explained by pressure induced transition from Cr 2+ high spin state to Cr 2+ low spin state. All pressure induced changes are reversible.

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