Multifunctional materials based on the double-perovskite organic-inorganic hybrid (CH3NH3)2[KCr(CN)6] showing switchable dielectric, magnetic, and semiconducting behaviour.

Herein, we have synthesised and characterised a novel organic-inorganic hybrid crystal, [CH3NH3]2KCr(CN)6 (MACr). Thermal analysis (DSC, TGA-DTA) indicates one structural phase transition (PT) at 450 K. The modified equation of the tolerance factor, t, was used to estimate the theoretical PT temperature for a crystal with Mn(iii). According to the X-ray diffraction experiment, in the low-temperature (LT) phase, the solid-to-solid PT is described by the monoclinic space group C2/c. The creation of the ferroelastic domain structure in phase II was proved on the basis of the observation under a polarising microscope. The crystals of MACr and its isomorphous analogues with Fe(iii) and Co(iii) appeared to be semiconducting materials in the LT phase. The type of PT is order-disorder and occurs between "low" (ordered-frozen) and "high" (orientationally disordered) dielectric states. Dielectric spectroscopy was used to characterise the switching properties of the dipole moments in the vicinity of the PTs. The magnetic properties of the MACr hybrid were investigated in DC and AC modes. The DC data show a sizeable weak exchange interaction between the nearest Cr(iii) centres in the crystal lattice. The AC susceptibility data confirm a slow magnetic relaxation in the applied DC field with two relaxation channels. The low-frequency relaxation time is very long as τLF = 1.4(1) s at T = 2.0 K. The organic-inorganic hybrid, described above, can be considered a rare example of multifunctional materials which exhibit dielectric, magnetic, and conductive activities.

Field-Induced Slow Magnetic Relaxation in a Mononuclear Manganese(II) Complex.

A mononuclear manganese(II) complex, [Mn(4-bzpy)4Cl2] (4-bzpy = 4-benzylpyridine), exhibits a slow magnetic relaxation with three relaxation modes that is supported by the external magnetic field. The low-frequency mode shows an exceptionally slow relaxation time: τ = 798 ms at T = 1.9 K and BDC = 0.35 T. The high-frequency domain exhibits unusual acceleration of the relaxation time upon cooling below 3.5 K.

Field effects to slow magnetic relaxation in a mononuclear Ni(ii) complex.

A mononuclear Ni(ii) complex [Ni(NCS)2(nqu)2(H2O)2]·2nqu (nqu - 5-nitroquinoline) shows a field induced slow magnetic relaxation with three relaxation domains. The relaxation time for the low-frequency mode is as slow as τ = 0.3 s at T = 1.9 K and BDC = 0.4 T.

Slow magnetic relaxation in a Co(ii) octahedral-tetrahedral system formed of a [CoL3]2+ core with L = bis(diphenylphosphanoxido) methane and tetrahedral [CoBr4]2- counter anions.

A bimetallic Co(ii) compound [Co(dppmO,O)3][CoBr4] consisting of cationic octahedral and anionic tetrahedral units in the crystal lattice shows a sizable magnetic anisotropy and field-supported slow magnetic relaxation with the relaxation time τ = 0.1-0.3 s at T = 1.9 K.