Magnetic systems at criticality: different signatures of scaling

Different aspects of critical behaviour of magnetic materials are presented and discussed. The scaling ideas are shown to arise in the context of purely magnetic properties as well as in that of thermal properties as demonstrated by magnetocaloric effect or combined scaling of excess entropy and order parameter. Two non-standard approaches to scaling phenomena are described. The presented concepts are exemplified by experimental data gathered on four representatives of molecular magnets.Comment: 33 pages, 16 figure

Magnetization dynamics and coherent spin manipulation of a propeller Gd(III) complex with the smallest helicene ligand

A homoleptic gadolinium(III) complex with the smallest helicene-type ligand, 1,10-phenanthroline-N,N'-dioxide (phendo) [Gd(phendo)(4)](NO3)(3)center dot xMeOH (phendo = 1,10-phenanthroline-N,N'-dioxide, MeOH = methanol), shows slow relaxation of the magnetization characteristic for Single Ion Magnets (SIM), despite negligible magnetic anisotropy, confirmed by ab initio calculations. Solid state dilution magnetic and EPR studies reveal that the magnetization dynamics of the [Gd(phendo)(4)](3+) cation is controlled mainly by a Raman process. Pulsed EPR experiments demonstrate long phase memory times (up to 2.7 mu s at 5 K), enabling the detection of Rabi oscillations at 20 K, which confirms coherent control of its spin state.</p

Enforcing Multifunctionality: A Pressure-Induced Spin-Crossover Photomagnet

Photomagnetic compounds are usually achieved by assembling preorganized individual molecules into rationally designed molecular architectures via the bottom-up approach. Here we show that a magnetic response to light can also be enforced in a nonphotomagnetic compound by applying mechanical stress. The nonphotomagnetic cyano-bridged Fe^II–Nb^IV coordination polymer {[Fe^II(pyrazole)₄]₂[Nb^IV(CN)₈]·4H₂O}_<i>n</i> (<b>FeNb</b>) has been subjected to high-pressure structural, magnetic and photomagnetic studies at low temperature, which revealed a wide spectrum of pressure-related functionalities including the light-induced magnetization. The multifunctionality of <b>FeNb</b> is compared with a simple structural and magnetic pressure response of its analog {[Mn^II(pyrazole)₄]₂[Nb^IV(CN)₈]·4H₂O}_<i>n</i> (<b>MnNb</b>). The <b>FeNb</b> coordination polymer is the first pressure-induced spin-crossover photomagnet

The cyanido bridged clusters with the remote N oxide groups for branched multimetalic systems

The combination of [W^V(CN)₈]^3– anions with 3d metal cations M^II in MeOH leads to the formation of pentadecanuclear spherical cyanido-bridged clusters {M­[M­(solv)₃]₈[M′(CN)₈]₆}, <b>M</b>_<b>9</b><b>M′</b>_<b>6</b>. By decorating their surface with organic ligands or/and by installation of different ions in their coordination skeleton, one could tune high spin in the ground state, slow relaxation of magnetization, or structural/spin phase transition. In this work we present the extended molecular high spin (<i>S</i>_GS = ¹⁵/₂, <i>g</i>_eff = 3.4) clusters or chains of clusters {Co₉W₆(<i>N</i>,<i>O</i>-L)_<i>x</i>} (<i>N</i>,<i>O</i>-L – pyrazine mono-N-oxide, <i>pzmo</i>; 4,4-bipyridine mono-N-oxide – 4,4′-<i>bpmo</i>) equipped with the structurally ordered remote (2–2.5 nm) N-oxide functions, as a result of deliberate combination of solvated Co₉W₆ supercomplexes with asymmetric <i>N</i>,<i>O</i>-donor linkers L. The systematic occurrence of such motifs in the series <b>1</b>–<b>3</b> is a result of preference for the Co–N_L coordination over the Co–O_L coordination, controlled also by strongly competing supramolecular interactions including simple hydrogen bonding {_LNO···H-donor} as well as cooperative π-costacked hydrogen bonding in double cyclic synthons {Co–O–H_MeOH···O–N_bpmoN−}₂. The observed coordination backbones are discussed in terms of the potential to bind the specific external molecular units and create the new type of branched molecular organization. The magnetic properties are confronted with structural differences along <b>1</b>–<b>3</b>, considering coordination polyhedra, Co–N bond lengths, Co–N–C angles, and hydrogen bonds. The diversity of slow magnetic relaxation images for the known Co₉W₆ based phases are discussed in terms of local deformation of Co coordination polyhedra and global deformation of cyanide bridged backbones