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Exchange bias (EB) phenomena have been observed in Nd2/3Ca1/3MnO3 colossal magnetoresistance perovskite below the Curie temperature TC~70K and attributed to an antiferromagnetic-ferromagnetic (FM) spontaneous phase segregated state of this compound. Field cooled magnetic hysteresis loops exhibit shifts toward negative direction of the magnetic field axis. The values of exchange field HEB and coercivity HC are found to be strongly dependent of temperature and strength of the cooling magnetic field Hcool. These effects are attributed to evolution of the FM phase content and a size of FM clusters. A contribution to the total magnetization of the system due to the FM phase has been evaluated. The exchange bias effect decreases with increasing temperature up to TC and vanishes above this temperature with disappearance of FM phase. Relaxation of a non-equilibrium magnetic state of the compound manifests itself through a training effect also observed while studying EB in Nd2/3Ca1/3MnO3. [ABSTRACT FROM AUTHOR]

The exchange bias (EB) phenomenon has been found in Nd2/3Ca1/3MnO3 perovskite. The phenomenon manifests itself as a negative horizontal shift of magnetization hysteresis loops. The EB phenomenon is evident of an interface exchange coupling between coexisting antiferromagnetic (AFM) and ferromagnetic (FM) phases and confirms the phase separated state of the compound at low temperatures. The EB effect is found to be strongly dependent on the cooling magnetic field and the temperature, which is associated with the evolution of spontaneous AFM-FM phase separated state of the compound. Analysis of magnetic hysteresis loops has shown that ferromagnetic moment M FM originating from the FM clusters saturates in a relatively low magnetic field about H ~ 0.4 T. The obtained saturation value MFM(1 T) ~ 0.45 µB is in a good agreement with our previous neutron diffraction data. [ABSTRACT FROM AUTHOR]

From the systems Cu(II)–cyclam–[M(CN)4]2− (cyclam = 1,4,8,11-tetraazacyclotetradecane; M = Ni, Pd, Pt), three cyanidocomplexes Cu(cyclam)M(CN)4 [M = Ni (1), Pd (2), Pt (3)] were isolated and characterized by chemical analysis, IR and UV–VIS spectroscopy. The three compounds are isostructural, and their crystal structures are formed by quasi-linear chains exhibiting [–Cu(cyclam)–μ–NC–M(CN)2–μ–CN–]n composition. The Cu(II) atoms reside on centres of symmetry and are coordinated in the form of an elongated octahedron with mean equatorial Cu–N bonds of 2.015(12), 2.017(13) and 2.011(11) Å in (1), (2) and (3), respectively, and weakly N-bonded bridging cyanido ligands in the axial positions [2.5321(9) Å in (1), 2.518(2) Å in (2) and 2.549(3) Å in (3)]. Hydrogen bonds of the N–H···Ncyanido···H–N type link neighbouring chains, and a topologically square network of paramagnetic Cu(II) atoms is formed. The magnetic susceptibilities of all three complexes follow the Curie-Weiss law with a weak antiferromagnetic exchange coupling below 5 K. [ABSTRACT FROM AUTHOR]

Abstract: Magneto-structural correlations in Mn(en)Ni(CN)4 (en = ethylenediamine) (MENC) have been studied. The crystal structure of MENC was refined by Rietveld analysis of X-ray powder diffraction data; it is three-dimensional (3d) and is built up of [Mn(en)]2+ cations with deformed octahedrally coordinated Mn(II) atoms and [Ni(CN)4]2− anions containing square-planarly coordinated Ni(II) atoms. The building species are linked by bridging -cyano ligands. The characterization of magnetic properties confirmed the expected 3d nature of spin correlations by observing λ-like anomaly in specific heat at . The resulting exchange interaction is somewhat smaller than that found in other complexes with the same type of exchange paths. [Copyright &y& Elsevier]

Abstract: The polymeric complex, {[Cu(tmen)][Pt(CN)4]} n (tmen =tetramethylethylenediamine) has been synthesized and characterized by elemental analysis, infrared spectroscopy, single-crystal structure analysis and by measurement of magnetic properties. Four ν(C N) absorption bands have been recorded in the infrared spectrum of this compound, what corresponds with four different types of cyano groups in the structure. Crystal structure revealed that one cyano group is terminal whereas three crystallographically different cyano groups of [Pt(CN)4]2− anions bridge Pt(II) and Cu(II) atoms to form a two-dimensional structure with a weak antiferromagnetic exchange coupling. [Copyright &y& Elsevier]

Abstract: We have studied by the electron-spin resonance (ESR) and static magnetic field techniques, the La2/3Ba1/3MnO3 perovskite, which was previously shown to exhibit a martensitic phase transformation in the vicinity of T s ∼200K [Physical Review B 68, 054109 (2003)], leading to its structural phase-segregated state. Resonant absorptions reveal that in the temperature interval from 100K to 340K the compound represents a mixture of two ferromagnetic phases possessing different magnetizations, in varying proportions depending on the temperature, and a small amount of a paramagnetic phase. The results agree well with the previous neutron diffraction study. Applied in the ESR experiments, magnetic fields (2–6kOe) strongly affect the magnetization curves: even magnetic field as high as 700Oe modifies the anomaly in the phase transformation region and removes the difference between the zero-field cooled and field-cooled magnetization curves, which implies that the difference in the magnetic susceptibility of the coexisting phases is small and the magnetic domain configuration can be easily changed. [Copyright &y& Elsevier]

Abstract: A detailed study of the low-temperature magnetic state and the relaxation in the phase-separated colossal magnetoresistance Nd2/3Ca1/3MnO3 perovskite has been carried out. Clear experimental evidence of the cluster-glass magnetic behavior of this compound has been revealed. Well defined maxima in the in-phase linear ac susceptibility χ′(T) were observed, indicative of the magnetic glass transition at T g ∼60K. Strongly divergent zero-field-cooled and field-cooled static magnetizations and frequency dependent ac susceptibility are evident of the glassy-like magnetic state of the compound at low temperatures. The frequency dependence of the cusp temperature T max of the χ′(T) susceptibility was found to follow the critical slowing down mechanism. The Cole–Cole analysis of the dynamic susceptibility at low temperature has shown extremely broad distribution of relaxation times, indicating that spins are frozen at “macroscopic” time scale. Slow relaxation in the zero-field-cooled magnetization has been experimentally revealed. The obtained results do not agree with a canonical spin-glass state and indicate a cluster glass magnetic state of the compound below T g , associated with its antiferromagnetic–ferromagnetic nano-phase segregated state. It was found that the relaxation mechanisms below the cluster glass freezing temperature T g and above it are strongly different. Magnetic field up to about μ 0 H∼0.4T suppresses the glassy magnetic state of the compound. [Copyright &y& Elsevier]

Abstract: The low temperature specific heat and magnetic characteristics of Nd2/3Ca1/3MnO3 perovskite are studied in a wide range of magnetic fields (up to 9T). Temperature dependent specific heat data show a broadened Schottky-like anomaly below 20K caused by splitting of the Nd3+ ions ground-state doublet in the effective molecular field H ex , determined by exchange interaction between Nd and Mn spin systems supplemented by an applied external magnetic field. Existence of the splitting at zero magnetic field and expressed field dependence is the evidence of a strong exchange coupling between Nd and Mn magnetic subsystems. The Nd-ions magnetic ordering leads to an additional contribution to the magnetic moment of the system below 30K, producing anomalies of the magnetic loss and field-cooled and zero-field-cooled magnetizations. The observed broadened Schottky-like anomalies are fitted for each applied magnetic field by the sum of three Schottky functions. Applied magnetic field extends the anomaly region and shifts it to higher temperatures. Splitting of the higher crystal field Kramers doublets gives an additional contribution to the heat capacity in magnetic fields. The ground state doublet g-factors g || and g ⊥ were estimated to be 3.4 and 2.2, respectively, and H ex was estimated to be 9T. The Nd3+ ions magnetic moment estimated from the magnetization data agrees with the value obtained from the specific heat data. [Copyright &y& Elsevier]

Abstract: Violet (1) and blue (2) polymorphous modifications of [Cu(men)2Pt(CN)4] n (men = N-methyl-1,2-diaminoethane) have been prepared and investigated by IR and UV–vis spectroscopy, thermal analysis, measurement of magnetic data and X-ray structural analysis. Both modifications are formed by similar but differently packed zigzag chains, which consist of [Cu(men)2]2+ moieties bridged by two trans arranged cyanido groups of [Pt(CN)4]2− units. The Cu(II) atoms in both structures are hexacoordinated by four nitrogen atoms in the equatorial plane from two molecules of bidentate men ligands with the average Cu–N(Me) and Cu–N(H2) bond lengths of 2.046(8) and 2.008(8)Å, respectively, and by two nitrogen atoms from bridging cyanido groups in the axial positions at average distance of 2.50(7)Å. Broad nearly symmetric bands observed in the UV–vis spectra of 1 and 2 of 2 B 1g → 2 E g transitions are consistent with a deformed octahedral coordination of the CuN6 chromophoric groups. One and two ν(Ction bands observed in the IR spectra of 1 and 2, respectively, are in agreement with different local symmetries of [Pt(CN)4]2− units and different Cu–N(cyanido) bond lengths in these polymorphs and are subject of discussion on the spectral–structural correlations in 1D compounds. The complexes are stable up to 238°C when their two-stage thermal decompositions start and ending up with a mixture of CuO and metallic Pt as the most probable final thermal decomposition products. The temperature dependence of the magnetic susceptibility suggests the presence of aweak antiferromagnetic exchange coupling between Cu(II) atoms in 1, J/hc =−0.17cm−1 and in 2, J/hc =−1.3cm−1. [ABSTRACT FROM AUTHOR]

Abstract: New bimetallic compound [Cu x Ni1−x (bpy)2(ox)]·4H2O (x =0.05, ox=oxalato, bpy=2,2′-bipyridine) was synthesized and chemically characterized. Its crystal structure is molecular. The octahedron around the metal central atom is deformed due to coordination by one bidentate oxalate anion and two bpy ligands. There are four uncoordinated water molecules in the asymmetric unit. The metal site is occupied by both Cu(II) and Ni(II) atoms in the 5:95 ratio. The complex molecules interact with water molecules through hydrogen bonds and, moreover, π–π interactions between aromatic rings lead to a 1D arrangement of molecules. The susceptibility data measured down to 2K were analyzed using strong-coupling theory and the best agreement with the experimental data were found for g =2.1, D/k =5.6, E/k =0.35, J/k =0.2. The dehydration starts at 30°C. As a final product of its thermal decomposition a solid solution of Cu x Ni1−x O was detected by X-ray powder diffraction. [Copyright &y& Elsevier]

Abstract: The synthesis, structural analysis, spectroscopic studies, susceptibility and specific-heat measurements of {[Cu(bmen)2][Pt(CN)4]} n (bmen=N,N′-dimethylethylenediamine) are presented. X-ray crystal-structure analysis revealed that the [Pt(CN)4]2− building blocks are combined with [Cu(bmen)2]2+ units to form a chain-like structure along the a axis. The Cu(II) atoms are hexacoordinated by four nitrogen atoms in the equatorial plane belonging to two molecules of bidentate bmen ligands with average Cu–N distance of 2.043(18)Å. The axial positions are occupied by two nitrogen atoms from bridging [Pt(CN)4]2− anions at a longer axial Cu–N distance of 2.490(4)Å. The compound is characterized by the presence of a weak antiferromagnetic exchange coupling J/kB =0.6K. Despite the one-dimensional (1D) character of the structure, the analysis of the magnetic properties and specific heat at very low temperatures shows that [Cu(bmen)2][Pt(CN)4] behaves as a two-dimensional (2D) square-lattice Heisenberg magnet with weak interlayer coupling. [Copyright &y& Elsevier]

Abstract: Crystal structure, thermodynamic properties and electron spin resonance spectra of Cu(NH3)2Ag2(CN)4 have been studied. The structure of the studied compound consists of interpenetrating wave-shaped two-dimensional (2d) arrays, in which CuN4N2 octahedra axially elongated due to the Jahn–Teller effect are linked by diamagnetic [Ag(CN)2]− anions forming a square lattice. Although the susceptibility and specific heat data confirm the existence of short-range order at about 2K, quantitative analysis of the experimental data reveals that the magnetic behavior differs from that of the crystal structure expected for 2d Heisenberg magnet on the square lattice. Structural features responsible for the observed difference are discussed. In addition, it is suggested, that additional degrees of freedom contribute to the thermodynamic equilibrium properties in the millikelvin temperature range. [Copyright &y& Elsevier]

Abstract: New radical cation salt of bis(ethylenedithio)tetrathiafulvalenium and iron bis(dicarbollide) [BEDT-TTF]2[3,3′-Fe(1,2-C2B9H11)2] (1) has been synthesized. The crystal structure of 1 has been determined by single-crystal X-ray diffraction method found to be isostructural to the known Co and Cr analogues. The electric conductivity measurement in the range of 110÷296 К shows that 1 is semiconductor with the room temperature conductivity σ293 =1.5×10−2 Ω−1 cm−1, that is higher than in the Cr analogue and lower than in the Co analogue. The measurement of magnetic susceptibility in the range of 2÷300K revealed that 1 is paramagnetic with the absence of significant interactions between the organic radical cations and the paramagnetic anions. [Copyright &y& Elsevier]