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ABSTRACT: We present a complete characterization of the ferromagnetic system CeIr2B2 using powder x-ray diffraction (XRD), magnetic susceptibility χ(T), isothermal magnetization M(H), specific heat C(T), electrical resistivity ρ(T,H), and thermoelectric power S(T) measurements. Furthermore, 11B NMR study was performed to probe the magnetism on a microscopic scale. Rietveld refinement of powder XRD data confirms that CeIr2B2 crystallizes in CaRh2B2-type orthorhombic structure (space group fddd). The χ(T), C(T), and ρ(T) data confirm bulk ferromagnetic ordering with Tc=5.1 K. Ce ions in CeIr2B2 are in a stable trivalent state. Our low-temperature C(T) data measured down to 0.4 K yield a Sommerfeld coefficient γ = 73(4) mJ/mol K2, which is much smaller than the previously reported value of γ = 180 mJ/mol K2 deduced from the specific heat measurement down to 2.5 K. For LaIr2B2, γ = 6(1) mJ/mol K2, which implies the density of states at the Fermi level D(EF)=2.54 states/(eV f.u.) for both spin directions. The renormalization factor for quasiparticle density of states and hence for quasiparticle mass due to 4 f correlations in CeIr2B2 is ≈12. The Kondo temperature TK∼4 K is estimated from the jump in specific heat of CeIr2B2 at Tc. Both C(T) and ρ(T) data exhibit a gapped-magnon behavior in the magnetically ordered state with an energy gap Eg∼3.5 K. The ρ data as a function of magnetic field H indicate a large negative magnetoresistance (MR) which is highest for T=5 K. While at 5 K the negative MR keeps on increasing up to 10 T, at 2 K an upturn is observed near H=3.5 T. On the other hand, the thermoelectric power data have small absolute values (S∼7μV/K), indicating a weak Kondo interaction. A shoulder in S(T) at about 30 K, followed by a minimum at ∼10 K, is attributed to crystal electric field effects and the onset of magnetic ordering. 11B NMR line broadening provides strong evidence of ferromagnetic correlations below 40 K.
Physical Review B 07/2012; 86:014414. · 3.69 Impact Factor
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ABSTRACT: We have investigated the magnetic properties of polycrystalline Y bRu2(Ge1 − xSix)2 samples using magnetic susceptibility, electrical resistivity, and specific heat measurements. All the results indicate that the Yb ions in Y bRu2(Ge1 − xSix)2 are in a stable trivalent state. The antiferromagnetic ordering shifts to lower temperature with increasing Si concentration (x). The weak Kondo-like resistivity minimum observed in the resistivity data for x = 0 shifts toward lower temperature with an increase in the Si content and finally disappears. The most dramatic observation is the complete suppression of the quadrupolar ordering in Y bRu2Ge2 (TQ = 10 K) even for 2% Si doping.
Journal of Physics Condensed Matter 03/2010; 22(12):126004. · 2.55 Impact Factor
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ABSTRACT: We have investigated the magnetic properties of polycrystalline Y bRu(2)(Ge(1 - x)Si(x))(2) samples using magnetic susceptibility, electrical resistivity, and specific heat measurements. All the results indicate that the Yb ions in Y bRu(2)(Ge(1 - x)Si(x))(2) are in a stable trivalent state. The antiferromagnetic ordering shifts to lower temperature with increasing Si concentration (x). The weak Kondo-like resistivity minimum observed in the resistivity data for x = 0 shifts toward lower temperature with an increase in the Si content and finally disappears. The most dramatic observation is the complete suppression of the quadrupolar ordering in Y bRu(2)Ge(2) (T(Q) = 10 K) even for 2% Si doping.
Journal of Physics Condensed Matter 03/2010; 22(12):126004. · 2.55 Impact Factor
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ABSTRACT: We have grown single crystals of YbNiB(4) using a Ni(60)B(40) flux and determined the magnetic properties of this compound by means of magnetic susceptibility, specific heat and electrical resistivity measurement. Yb ions in YbNiB(4) are in a trivalent state and present a transition from a paramagnetic state to an antiferromagnetic (AF) state at T(N1) = 5.4 K and a further transition towards a second AF state at T(N2) = 4.0 K. Kondo type behavior in the resistivity and an enhanced Sommerfeld coefficient γ = 100 mJ mol(-1) K(-2) provide evidence for a significant Kondo interaction. A broad maximum in χ(T) at around 8 K, well above T(N1), suggests low-dimensional antiferromagnetic correlations. Both mechanisms lead to strong fluctuation in an extended temperature range above T(N1), up to the characteristic energy of this system, which was estimated to be T(4f) = 16 K from an analysis of the entropy.
Journal of Physics Condensed Matter 05/2009; 21(20):206003. · 2.55 Impact Factor
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ABSTRACT: We present a complete characterization of the magnetic properties of indium-flux grown single crystals of EuIr2Ge2 using electrical resistivity, magnetization, specific heat, magnetoresistance and 151Eu Mössbauer spectroscopy. All results indicate that Eu ions in EuIr2Ge2 are in the divalent state with Eu moments ordering antiferromagnetically at TN = 20.5 K. While at higher temperatures the susceptibility χ is isotropic as expected for the pure spin nature of the Eu local moment, below 40 K a pronounced anisotropy emerges, with χab in the basal plane being a factor of two larger than χc along c at TN. We observed a pronounced metamagnetic transition in the in-plane magnetization, which is also reflected in a step-like increase of the magnetoresistance. Further analysis of the data indicates that the metamagnetic transition is related to a spin–flop transition. The origin of this strong anisotropy and of the pronounced metamagnetic transition is discussed.
Journal of Physics Condensed Matter 06/2008; 20(28):285217. · 2.55 Impact Factor
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ABSTRACT: The effect of 2 mol % of P2O5 or TiO2 on the crystallization of yttrium-iron-garnet (YIG) in Na2O-SiO2-Y2O3-Fe2O3 glass ceramics has been investigated by X-ray and Mssbauer spectroscopic studies. These studies indicate that the glass ceramics containing P2O5 are more favourable for the crystallization of YIG. Analysis of the results suggest that an optimum growth temperature for crystallization of the YIG phase is 800 C in the sample with P2O5 as the nucleating agent. The sample heat-treated at the growth temperature for 40 h is not as favourable for crystallization of the YIG phase as the sample which is given a two-stage heat-treatment.
Journal of Materials Science 08/1984; 19(9):3021-3027. · 2.02 Impact Factor
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ABSTRACT: The effect of 2 mol % of P2O5 or TiO2 on the crystallization of yttrium-iron-garnet (YIG) in Na2O-SiO2-Y2O3-Fe2O3 glass ceramics has been investigated by X-ray and Mössbauer spectroscopic studies. These studies indicate that the glass ceramics containing P2O5 are more favourable for the crystallization of YIG. Analysis of the results suggest that an optimum growth temperature for crystallization of the YIG phase is 800° C in the sample with P2O5 as the nucleating agent. The sample heat-treated at the growth temperature for 40 h is not as favourable for crystallization of the YIG phase as the sample which is given a two-stage heat-treatment.
Journal of Materials Science - J MATER SCI. 01/1984; 19(9):3021-3027.
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Journal of Physics: Condensed Matter, v.21, 206003-1-206003-5 (2009).
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Journal of Physics: Condensed Matter, v.22, 126004-1-126004-4 (2010).
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Journal of Magnetism and Magnetic Materials, v.322, 2545-2549 (2010).
