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Magnetic properties of single crystalline HoCoC 2 and the evolution of magnetic and structural features in a series of polycrystalline solid solutions HoCo 1− x Ni x C 2 ( 0 ⩽ x ⩽ 1 ) are investigated by means of X-ray diffraction, magnetization, magnetic susceptibility and specific heat measurements. The crystal structures of all investigated samples refers to the CeNiC 2 -type structure (space group Amm 2 and Pearson symbol oS8). Non-isoelectronic substitution of Co by Ni causes a non-linear increase of the unit cell volume and especially a non-monotonous variation of the a and c lattice parameters as well as a pronounced reduction of the C–C bond length of carbon dimers. Temperature dependent magnetization and specific heat measurements reveal a crossover from a ferromagnetic for HoCoC 2 with T C = 10.6 (1) K to an antiferromagnetic ground state for HoNiC 2 with T N = 2.78 (6) K and a non-monotonous variation of the magnetic ordering temperature with a minimum at intermediate compositions. Crystalline electric field effects of HoCoC 2 and HoNiC 2 are analysed using combined thermodynamic and magnetic susceptibility data. The electrical resistivity of HoNiC 2 displays a distinct anomaly near room temperature which indicates the formation of a charge density wave (CDW) state as earlier reported for several other rare earth nickel dicarbides.

The crystal structure of the solid solution of DyCo1−хNiхC2 (0≤x≤1) was investigated by means of X-ray powder diffraction: structure type CeNiC2, space group Amm2, and Pearson symbol oS8. The structural analysis reveals a non-monotonous evolution in particular for the a- and c-lattice constants resulting in a non-linear increase of the unit cell volume due to non-isoelectronic substitution of Co by Ni markedly deviating from Vegard׳s law. A crossover from ferro- to antiferromagnetic ordering with a significant reduction of the magnetic ordering temperature at intermediate compositions in DyCo1−хNiхC2 is observed when varying the Ni-concentration. A crossover from ferro- to antiferromagnetic coupling is also revealed from a sign change of the paramagnetic Curie temperature when proceeding along this solid solution.

Elastic and inelastic neutron scattering and magnetization measurements have been used to study peculiarities of the magnetic state in R{sub 3}T compounds (R=Gd, Er, Tb; T=Ni, Co) below and above magnetic ordering temperatures. A pronounced non-Brillouin shape of the magnetization curves observed in the antiferromagnetic compounds Gd{sub 3}Ni and Tb{sub 3}Ni above their magnetic ordering temperatures together with earlier reported data about the retention of the magnetic contribution to the total specific heat of Gd{sub 3}T and anomalous behavior of the electrical resistivity above magnetic ordering temperatures are ascribed to the existence of short-range magnetic correlations in the wide temperature range in the paramagnetic state. The persistence of short-range magnetic order up to temperatures greater than 5-6 times the Neel temperature has been revealed by powder neutron diffraction measurements performed for Tb{sub 3}Ni and Tb{sub 3}Co. On the other hand, results from inelastic neutron scattering show that the low temperature magnetic excitations are strongly suppressed in both Tb{sub 3}Co and Er{sub 3}Co. It is suggested that the extended short-range magnetic correlations, which turn out to be an inherent feature of R{sub 3}T type compounds, are due to the layered crystal structure and to the difference between geometrically frustrated intra-layer exchangemore » interactions and inter-layer exchange.« less

The magnetic entropy change in GdCo 13− x Si x ( x =3.8, 4, 4.1, and 4.2) intermetallic compounds has been investigated by means of magnetic measurements in the vicinity of their Curie temperature. It was found that the magnetic ordering temperatures decrease from 60 K at x =3 . 8 to 28 K for x =4 . 2. The magnetic entropy change is calculated from isothermal magnetization versus magnetic field at various temperatures using the Maxwell relation. As a result, the maximum magnetic entropy changes of the investigated compounds, at their Curie temperatures, decrease from 11.5 J/kg K for x =4.2 to 6.86 J/kg K for x =3.8 in a field change of 0–3 T, whereas it decreases from 5.13 J/kg K for x =4.2 to 2.60 J/kg K for x =3.8 in a field change of 0–1 T. Moreover, the maximum value of the magnetic entropy change obtained at a higher field for GdCo 13− x Si x with x =4 (23.75 J/kg K at 5 T) is comparable to that of various types of compounds with a cubic NaZn 13 -type structure. Finally, the maximum of the magnetic entropy change is found to decrease with increasing Si content.

The borocarbides R Ni 2 B 2 C ( R = magnetic rare earth) exhibit rich H–T magnetic phase diagrams. Using field-dependent specific heat measurements on single-crystals of R Ni 2 B 2 C ( R = Gd , Er), this work investigated the magnetic contribution to the specific heat when T and H are varied across these H–T phase diagrams. These measurements, together with the ones reported on HoNi 2 B 2 C , confirm that the overall evolution of each C mag ( T , H ) curve is a faithful reflection of the features observed in the corresponding phase diagram: in particular the successive field-induced metamagnetic modes, appearing in the reported magnetization M ( T , H ) curves, are also manifested in these C mag ( T , H ) curves, just as required by the Maxwell identity ( ∂ C mag / ∂ H ) T = T ( ∂ 2 M / ∂ T 2 ) H . Within the lower ranges of temperature and fields, the calculations based on linearized field-dependent spin-wave theory are found to reproduce satisfactorily the measured C mag ( T , H ) curves: accordingly, within these ranges, the thermodynamical properties of these compounds can be rationalized in terms of only two parameters, namely, the spin-wave energy gap and the stiffness coefficient. Based on the satisfactory agreement between theory and experiment, we are able to provide an explanation for the plateau like behavior observed in, say, the M ( T , H ) isotherms. Finally, for the particular case of GdNi 2 B 2 C wherein the anisotropy is dictated solely by the classical dipole interactions, the main features of its C mag ( T , H ) are found to be reproduced by numerical calculations based on the model of Jensen and Rotter [Phys. Rev. B 77 (2008) 134408].

Nanocrystalline zinc-substituted cobalt ferrite powders, Co 1− x Zn x Fe 2 O 4 ( x =0, 0.2, 0.4), were for the first time prepared by forced hydrolysis method. Magnetic and structural properties in these specimens were investigated. The average crystallite size is about 3.0 nm. When the zinc substitution increases from x =0 to x =0.4, at 4.2 K, the saturation magnetization increases from 72.1 to 99.7 emu/g and the coercive field decreases from 1.22 to 0.71 T. All samples are superparamagnetic at room temperature and ferrimagnetic at temperatures below the blocking temperature. The high value of the saturation magnetization and the very thin thickness of the disorder surface layer of all samples suggests that this forced hydrolysis method is suitable not only for preparing two metal element systems but also for three or more ones.

Magnetic properties of melt-spun Nd 60 Fe 30 Al 10 alloy were studied between 2 and 350 K. The behaviour of the temperature dependence of coercive field is explained by the presence of magnetic multi-phases, which were determined by means of transmission electron microscopy and X-ray diffraction. Low coercivity at room temperature is attributed to the low Curie temperature of the amorphous phase.

CePt 2 Si crystallizes in the inverse CeNiSi 2 -type structure. Magnetic properties are dominated by a mutual interaction of the RKKY interaction, the Kondo effect and crystalline electric field splitting, resulting in long range magnetic order below about 7 K . A slightly enhanced Sommerfeld value γ = 42 mJ / mol K 2 and a distinct temperature dependence of the electrical resistivity refers to Kondo interaction in presence of strong crystalline electric field splitting.

The tetragonal compounds PrCo9Si4 and NdCo9Si4 have been studied by specific heat, electrical resistivity and magnetic susceptibility measurements. The onset of ferromagnetic order is observed at Curie temperatures TC≃24 and 12 K for PrCo9Si4 and NdCo9Si4, respectively. Thermodynamic and transport data of both compounds reveal a first-order phase transition from the paramagnetic to the ferromagnetic state which can be deduced from step like anomalies in the resistivity data as well as sharp peak-type anomalies of the specific heat.

We present results of magnetisation, resistivity, thermopower and thermal conductivity measurements on the compound Eu 0.83 Fe 4 Sb 12 , which orders magnetically below 84 K. An interesting feature of this compound is the large positive magnetoresistance, reaching values of 130% at 2 K and 12 T, and still 30% at room temperature. Fe/Co substitution causes a drop in the magnetic ordering temperature T mag and an increase of the thermopower values, which is expected from a decrease of the charge carrier density.

Pr 0.73 Fe 4 Sb 12 orders magnetically below about 5.5 K . Magnetic order disappears upon Fe substitution by Ni or Co. The Seebeck coefficients is strongly influenced by the Fe/(Ni,Co) substitution and reaches values of up to 230 μV/K at about 450 K . Thus this series of compounds represents an attractive candidate for future thermoelectric applications.

A Sn/In substitution in ternary Yb2Pd2In provokes a crossover from a Kondo-dominated regime (In-rich) to a ground state governed simultaneously by RKKY interaction, crystal field splitting and the Kondo effect. Consequently, long-range magnetic order develops. However, the Kondo effect becomes again of primary importance when approaching Yb2Pd2Sn. The low-temperature physics of samples rich in In is characterised by significant deviations from a Fermi-liquid scenario.

We report on non-Fermi liquid features observed for CeNi 9 Ge 4 —a novel stoichiometric compound, which is close to the heavy-fermion quantum critical point. The specific heat measured down to 80 mK reveals an almost logarithmic divergence of the low-temperature contribution yielding an extraordinarily large Sommerfeld value γ exceeding 6 J / mol K 2 . The application of external magnetic fields recovers a conventional Fermi-liquid state.

The giant enhancement of the coefficient γ of the T-linear specific heat, retention of the magnetic contribution to the total specific heat above the ordering temperature and anomalous behavior of the temperature dependencies of the electrical resistivity in the paramagnetic region have been revealed by specific heat and electrical resistivity measurements for some R3M (M=Co, Ni, Rh). Such a behavior is associated with the presence of a huge contribution from spin fluctuations induced by the f–d exchange in the itinerant d-electron subsystem.

For a limited range of concentration and pressure the itinerant Co sublattices orders magnetically at TCoC which is lower than TRC of the localized R sublattice. A field-induced collapse of the Co moment as function of both concentration and pressure is observed and ascribed to an inverse itinerant electron metamagnetism.

YbCu 4 Au x Ag 1− x provides the possibility to study a crossover from high to low T K systems and therefore from coherent to incoherent behaviour. Although this series is isoelectronic, details in the electronic structure appear to be the driving force for different ground state properties, rather than chemical pressure due to the Au/Ag substitution.

Electrical resistivity, specific heat and magnetic phase transitions have been studied in Mn 1.8 Co 0.2 Sb and FeRh based compounds, where Fe and Rh are substituted by other d elements (Ni, Pd, Pt, Ir, Ru). In the antiferromagnetic state below a critical temperature, T t , an external field induces first-order phase transitions accompanied by a giant magnetoresistance effect (of about −60% at room temperature) and by a significant enhancement of the electronic specific heat coefficient (up to 180%), which are both strongly affected by the d electron concentration.

We present specific heat measurements of the title compounds and discuss the results in connection with their magnetic properties.