Analysis Of Magnetic Specific Heat Research Articles

Magnetic properties of Cu[C6H2(COO)4][H3N–(CH2)2–NH3]·3H2O - A quasi-two-dimensional S = 1/2 antiferromagnet on rectangular lattice

The analysis of specific heat, magnetic susceptibility and magnetization identified the studied compound Cu[C6H2(COO)4][H3N–(CH2)2–NH3]·3H2O as a quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet on the rectangular lattice with the intrachain coupling J1/kB≈ 7.39 K and the interaction ratio R ≈ 0.44. A phase transition to a magnetically ordered state was observed in zero magnetic field at TN = 1.28 K. The analysis of magnetic specific heat in non-zero magnetic fields revealed features characteristic of the field-induced Berezinskii-Kosterlitz-Thouless phase transition theoretically predicted for ideal two-dimensional magnets. The electron paramagnetic resonance studies of Cu[C6H2(COO)4][H3N–(CH2)2–NH3]·3H2O revealed the increase of gx and gy and decrease of gz below 25 K due to the presence of dipolar coupling and the exchange anisotropy. The upturn of linewidth appearing below 30 K can be ascribed to the development of intralayer magnetic correlations.

Experimental study of the magnetocaloric effect in [Ni(fum)(phen)] – The ferromagnetic dimer with spin 1

[Ni(fum)(phen)] (fum = fumarato, phen = 1,10 -phenanthroline) has been identified as a system consisting of antiferromagnetic S = 1 dimers with single-ion magnetic anisotropy D comparable to the intradimer exchange coupling J, D/J ≈ 1 and D/kB = −6 K. We present reclassification of the physical model of [Ni(fum)(phen)] magnetic subsystem and the magnetocaloric investigation of a [Ni(fum)(phen)] powder sample at temperatures above 2 K in magnetic fields up to 7 T. The analysis of magnetic specific heat and magnetocaloric effect in [Ni(fum)(phen)] has shown that the temperature dependence of the isothermal entropy change under different magnetic fields is in good agreement with theoretical predictions for the S = 1 ferromagnetic dimer with D/kB = −11.5 K, E/kB = −3.4 K and intradimer exchange coupling J/kB = 2.5 K. Sizeable conventional magnetocaloric effect was found around 5.8 K leading to -ΔSmax = 8.2 Jkg−1K−1 for ΔB = 7 T.

Absence of a long-range ordered magnetic ground state in Pr3Rh4Sn13 studied through specific heat and inelastic neutron scattering

Signatures of absence of a long-range ordered magnetic ground state down to 0.36 K are observed in magnetic susceptibility, specific heat, thermal/electrical transport and inelastic neutron scattering data of the quasi-skutterudite compound Pr3Rh4Sn13 which crystallizes in the Yb3Rh4Sn13-type structure with a cage-like network of Sn atoms. In this structure, Pr3+ occupies a lattice site with D2d point symmetry having a ninefold degeneracy corresponding to J = 4. The magnetic susceptibility of Pr3Rh4Sn13 shows only a weak temperature dependence below 10 K; otherwise remaining paramagnetic-like in the range, 10 K–300 K. From the inelastic neutron scattering intensity of Pr3Rh4Sn13 recorded at different temperatures, we identify excitations at 4.5(7) K, 5.42(6) K, 10.77(5) K, 27.27(5) K, 192.28(4) K and 308.33(3) K through a careful peak analysis. However, no signatures of long-range magnetic order are observed in the neutron data down to 1.5 K, which is also confirmed by the specific heat data down to 0.36 K. A broad Schottky-like peak is recovered for the magnetic part of the specific heat, C4f, which suggests the role of crystal electric fields of Pr3+ . A crystalline electric field model consisting of 7 levels was applied to C4f which leads to the estimation of energy levels at 4.48(2) K, 6.94(4) K, 11.23(8) K, 27.01(5) K, 193.12(6) K and 367.30(2) K. The CEF energy levels estimated from the heat capacity analysis are in close agreement with the excitation energies seen in the neutron data. The Sommerfeld coefficient estimated from the analysis of magnetic specific heat is mJ K−2 mol-Pr which suggests the formation of heavy itinerant quasi-particles in Pr3Rh4Sn13. Combining inelastic neutron scattering results, analysis of the specific heat data down to 0.36 K, magnetic susceptibility and, electrical and thermal transport, we establish the absence of long-range ordered magnetic ground state in Pr3Rh4Sn13.

Crossover from one- to three-dimensional behavior in the S = 1/2 Heisenberg antiferromagnet Cu(N2H5)2(SO4)2

From experimental and theoretical analyses of magnetic and specific-heat properties, we present the complete magnetic phase diagram of the quasi-1D antiferromagnet Cu(N2H5)2(SO4)2. On cooling and at zero magnetic field this compound enters a 1D regime with short-range magnetic correlations, marked by a broad maximum in the specific heat and magnetic susceptibility at K, followed by a tridimensional antiferromagnetically ordered phase below K induced by small interchain couplings. The intermediate-temperature 1D regime can be modeled using exact quantum-transfer-matrix calculations, which offer a compatible description of the nonmonotonic behavior of as a function of the magnetic field, giving K for the intrachain exchange parameter. The analysis of magnetic specific-heat and susceptibility data at low temperature indicates that the interchain exchange couplings are an order of magnitude smaller than the coupling inside the chains.

Fingerprints of field-induced Berezinskii–Kosterlitz–Thouless transition in quasi-two-dimensional S=1/2 Heisenberg magnets Cu(en)(H2O)2SO4 and Cu(tn)Cl2

Organo-metallic compounds Cu(en)(H2O)2SO4 (en=C2H8N2) and Cu(tn)Cl2 (tn=C3H10N2) representing S=1/2 quasi-two-dimensional Heisenberg antiferromagnets with an effective intra-layer exchange coupling J/kB≈3K, have been examined by specific heat measurements at temperatures down to nominally 50mK and magnetic fields up to 14T. A comparative analysis of magnetic specific heat in zero magnetic field revealed nearly identical contribution of short-range magnetic correlations and significant differences were observed at lowest temperatures. A phase transition to long-range order was observed in Cu(en)(H2O)2SO4 at TC=0.9K while hidden in Cu(tn)Cl2. A response of both compounds to the application of magnetic field has rather universal features characteristic for a field-induced Berezinskii–Kosterlitz–Thouless transition theoretically predicted for ideal two-dimensional magnets.