Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

Abstract

We present a complete characterization of 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 11 B NMR study was performed to probe the magnetism on a microscopic scale. Rietveld refinement of powder XRD data confirms that CeIr2B2 crystrallizes 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 stable trivalent state. Our low-temperature C(T ) data measured down to 0.4 K yield Sommerfeld coefficient γ = 73(4) mJ/mol K 2 which is much smaller than the previously reported value of γ = 180 mJ/mol K 2 deduced from the specific heat measurement down to 2.5 K. For LaIr2B2 γ = 6(1) mJ/mol K 2 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 quasi-particle density of states and hence for quasi-particle mass due to 4f 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 gapped-magnon behavior in 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 ∼ 7 µV/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 (CEF) effects and the onset of magnetic ordering. 11 B NMR line broadening provides strong evidence of ferromagnetic correlations below 40 K.

Anomalous ferromagnetism and non-Fermi-liquid behavior in the Kondo lattice CeRuSi2

“…[40]). Observation of Kondo coherence features requires investigation at lower temperatures (cf., e.g., data for CeIr 2 B 2 [13]). The corresponding figure of merit ZT = α 2 T /ρκ (κ being heat conductivity) has a maximum at T = 250 K where it makes up about 0.6%.…”

“…[6]). The number of such materials gradually increases, including CePt [7], CeRu 2 Ge 2 [8], CeAgSb 2 , [9], CeRuPO [10], CeRu 2 M 2 X (M = Al, Ga; X = B, C) [11,12], CeIr 2 B 2 [13], hydrogenated CeNiSn [14].…”

Crystal electric field and possible coupling with phonons in Kondo lattice CeCuGa3

“…Under the effect of crystal field the (2J + 1)-fold degenerate ground state multiplet of Kramers ion Ce 3+ (J = 5/2) splits into three doublets. From the analysis of C mag (T ) data by three-level CEF scheme [24,42,43] we find that the first excited doublet is situated at 1 = 70 K and the second excited doublet at 2 = 240 K. The fit of C mag (T ) by this CEF level scheme is shown by the solid red curve in Fig. 1(c).…”

Ferromagnetic ordering in NpAl2: Magnetic susceptibility and Al nuclear magnetic resonance

“…To our knowledge, only one NMR experiment, made on skutterudite NpFe 4 P 12 (Np 4 þ , 5f 3 ), referred to the study of a ferromagnetic neptunium-based compound [9,10] and our data cannot unfortunately be compared to NpFe 4 P 12 due to the different oxidation state. The second explanation, is the possible sensing by the 27 Al nuclei of the ferromagnetic ordering already at room temperature as this effect can be visible in the NMR spectrum well above the ordering temperature [32,33]. Both propositions are discussed later in the text.…”