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Magnetic behaviour of multiferroic [C(NH2)3] [Cu(HCOO)3]

Guanidinium copper(II) formate, [C(NH 2 ) 3 ] [Cu(HCOO) 3 ] belongs to the family of metal- organic perovskites with the formula ABX 3 . It crystallizes in the orthorhombic space group Pna2 1 . Copper ions are octahedrally coordinated and mutually connected with anti-anti formate bridges forming a framework with nearly cubic cavities in which the guanidinium ions are located. Due to the Jahn-Teller effect of Cu(II) cation, the octahedral coordination is elongated. The framework consists of the Cu-formate chains in the crystallographic c-axis, where Cu ions inside the chain are linked with short bonds and Cu ions between the chains with the long bonds. In this work we have studied magnetic properties of [C(NH 2 ) 3 ][Cu(HCOO) 3 ] using MPMS5 SQUID magnetometer. Temperature dependence of magnetization showed a broad peak centered at 45 K which can be ascribed to antiferromagnetic order within the Cu-formate chains. Below 5 K the sharp rise of magnetization indicated a formation of complex 3D spin long range order. Hysteresis loops at the temperatures below 5 K showed a sharp increase of magnetization for the fields even lower than 50 Oe. Anisotropy could be seen in both M(T) and M(H) measurements. Measurement of transverse magnetic moment showed that if the field is lower than 1000 Oe in a-direction, the magnetization in c-direction is still bigger than the magnetization in a-direction, indicating large anisotropy and the c-axis as an easy axis. The effect of electric field (E~1kV/mm) on the magnetization could be seen in M(T) curves at temperatures below 5 K in a way that the magnetization curves with and without the electric field did not overlap. Search for the explanations of observed magnetic behaviour is in process considering the interesting crystal structure of this compound.

Metal-organic hybrid compounds, magnetic order, multiferroics

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