Low temperature specific heat of Cr-Fe-Si alloys

Low temperature specific heats of Cr-Fe-Si alloys with 3 at. % Si were investigated between 1.4°–4.2°K. The electronic specific heat coefficient γ essentially varies with transition metal electron concentration ( e/a) in the same manner as the Cr-Fe alloys but with the high γ peak slightly shifted to lower e/a. The shift of γ peak suggests transfer of electrons from Si atoms to the 3d magnetic subband of the transition elements.     

Low temperature specific heat of transition metals and alloys

The article reviews experimental results on the low temperature specific heat of the transition metals and their alloys. Particularly discussed are the variations of the electronic part on the basis of a complete compilation of measurements given.     

Low temperature specific heat of Ni-Co and Ni-Fe alloys

Values of the low temperature specific heat of f.c.c. Ni-Co and Ni-Fe alloys have been determined in the 1.2–8 K range with a relative accuracy of 10^-3 and analysed to separate the electron, phonon, magnon and hyperfine terms. Results are in good agreement with former data^5–7 and with theory: Gomes' model⁴ of a d-d tight-binding scattering in the dilute case, Hasegawa's^12,13 CPA calculations are both consistent with experiments.     

Ni-Zr amorphous alloys: Low temperature specific heat and superconductivity

The specific heat (C_p) of the amorphous alloys Ni_100-xZr_x for x = 75, 65, 55 and 35 was measured from 0.8K to 40K and the composition trends of the transition temperature T_c, the enhanced density of states at the Fermi level N_γ(_F) and the Debye temperatures θ_D(0), θ_D(T) established. For the three superconducting compositions (x=75, 65, 55) N_γ(E_F increases rapidly with increasing [Zr] in agreement with the trend in amorphous Cu-Zr alloys. However, for the Zr-Ni alloys the bare density of states $\text{N}{}_0\text{(E}{}_{\mathrm{F}}\text{) =}\text{N}{}_{\mathrm{\gamma }}\text{(E}{}_{\mathrm{F}}\text{)}\text{(1 + λ}{}_{\mathrm{p}}\text{)}$ increases strongly with [Zr] in contrast to the Zr-Cu alloys where it is reported to be almost constant. We conclude that for the Ni-Zr alloys the electron-ion matrix element <I²> decreases with increasing [Zr]. Other results are related to recent photoemission studies of these alloys.     

Low temperature magnetic and electrical properties of DHCP Ce-La alloys

Electrical resistivity and magnetic susceptibility measurements on CeLa alloys have shown that 5% La in βCe (dhcp) stabilizes βCe with respect to αCe, preventing β from transforming to α in the 15–50 K region. The remarkable Kondo-like properties of pure βCe are also found in the alloys over a wide concentration range.     

Low temperature specific heat of ErAs

The specific heat of a sintered sample of ErAs has been measured from 1.4–6.1 K. A single broad κ-like peak in the data occurs at 3.25K. The entropy associated with the peak is approximately R ln4 suggesting an $\text{S′ =}\text{3}\text{2}$ ground state.     

Low temperature heat capacity of Rh-Cu alloys

Reported here are the low temperature heat capacity data on a series of single phase fcc Rh-Cu alloys. The electronic heat capacity coefficient, γ, decreases rapidly up to 20 at % of copper in Rh and then stays constant to ～60 at % Cu after which decreases smoothly to the pure Cu value. This is interpreted as due to the initial partial filling of the d-band after which the conduction electron of Cu goes into the s-band. An attempt is made to understand the origins of the curious anomalies in the Debye temperature and microhardness data.     

Low temperature specific heat of Cu3Au

Contrary to a recent letter of Gavignet-Tillard and Hammann, it has been shown that ordering does have a significant effect on the electronic specific heat of Cu₃Au.     

Low temperature properties of Pr amorphous alloys

Starting from the Fert and Campbell Hamiltonian and assuming a suitable η-distribution, the magnetization and the specific heat for Pr amorphous alloys are evaluated in the molecular field approximation with ferromagnetic interaction.Recent low-temperature experimental data on the specific heat of Pr amorphous alloys are reasonably explained.     

Low temperature properties of magnetic films

The effect of surface oxides on the low temperature magnetic properties of permalloy films is reviewed. Emphasis is placed on the work of Hagedorn and Mitchell and coworkers. It is shown that the unidirectional anisotropy in permalloy (typically exhibited at temperatures below 40 °K) can be correlated with the presence of -Fe₂O₃ as detected in electron diffraction studies. A possible mechanism for the phenomena is discussed which hinges on the depression of the Morin transition in -Fe₂O₃ as a consequence of a change in thed spacing of the -Fe₂O₃.The author would like to thank Professors L. D. Roberts and C. S. Smith of the University North Carolina for their helpful discussions during the course of this work.     

Superconductivity under pressure and low temperature specific heat of ThPr alloys

Measurements of superconducting transition temperature under pressure and low temperature specific heat are presented for ThPr alloys. At 18.2 kbar the normal- to superconducting-state phase boundary extends beyond 50 at.% Pr. This system is discussed in terms of a non-magnetic singlet ground state for the Pr³⁺ ions due to crystal field splitting. A splitting scheme which varies with Pr concentration is proposed.     

Low temperature specific heat of single-domain and polydomain ferroelectric NaNO2

The specific heat of a NaNO₂ sample has been measured between 2 K and 40 K in both single-domain and polydomain states. In this region the specific heat of the single domain sample follows exactly the T³ dependence. A clear excess contribution which in this temperature range has a temperature dependence between T and T² has been detected for the polydomain sample. It is attributed to domain walls.     

Low temperature magnetic properties of NdCu2

μSR experiments on NdCu₂ give evidence for short range order below 25\ K above T_N=6.5\ K. No signal was detected between 16\ K and 1.2\ K where neutron scattering reveals an incommensurate spin structure. Below 1.2\ K the μSR signal is recovered and shows a rotation with 22 MHz. This is interpreted with a squaring up of Nd spins accompanied by a decrease of magnon excitations which is reflected in a decrease of damping of the muon signal. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low temperature magnetic properties of trimeric clusters

The degeneracy in the Heisenberg model of the three chromium clusters having D₃ symmetry is split by the antisymmetric exchange interaction. Based on this new energy level scheme, the low temperature behavior of the specific heat and magnetic susceptibility are reexamined.     

Lattice specific heat of copper based dilute alloys at low temperature

The low-temperature lattice specific heat of copper-based dilute alloys $\text{Cu}$ Sn, $\text{Cu}$ Ga, $\text{Cu}$ Ge, $\text{Cu}$ Zn and $\text{Cu}$ Ni has been studied theoretically on the basis of Green's function theory. A nearest-neighbour impurity model, with certral and non-central force constant changes has been employed. The effect of volume change is taken into account, and is seen to be important. The calculated results are in excellent agreement with experimental measurements, and the derived force constants are seen to be reasonable.     

Low temperature heat capacity and magnetic excitation of HoAl2 in a magnetic field

The specific heat of single crystalline HoAl₂ in magnetic fields up to 7.5 T has been measured for the temperature range 1.5–16 K. In addition the energy of a magnetic excitation in a magnetic field of 5 T at 4.2 K has been determined by inelastic neutron scattering. The results have been interpreted with a cubic crystalline electric field and an exchange interaction using the same parameter set B₄=-0.85×10^-4 meV, B₆=+0.71× 10^-6 meV and T_C=31.5 K previously obtained by magnetization measurements.     

Transition temperature and specific heat discontinuity for superconducting alloys containing Kondo impurities

The dependence of the transition temperature and the specific heat discontinuity of a superconductor on the magnetic impurity concentration is calculated selfconsistently using the spin-boson approach for the Kondo problem. The results agree well with experimental dat for the (La, $\text{Ce}$) Al₂ alloy.     

Low temperature magnetic properties of Ti-rich Fe-Ti spinels

Low temperature hysteresis loops have been measured on compositions of the spinel series Fe_3-xTi_xO₄, 0?x?1, with x=0.4, 0.5, 0.6 and 0.8. All compounds studied exhibit an anomaly of the hysteresis parameters in the temperature range 40–80 K below which a marked effect of field cooling on the hysteresis loops is observed.     

Low temperature specific heat of dense kondo ferromagnets and intermediate valence CeNixPtt-x compounds

Specific heat measurements performed in the temperature range 1.5 to 30 K in the compounds CeNi_xPt_{1 - x} with x = 0.5, 0.8 and 0.95 are presented. The analysis of the magnetic entropy enhances the results obtained previously by magnetic measurements: i) the reduction of the cerium moment due to the Kondo effect; ii) the increase of the importance of the Kondo effect in competition with the RKKY interactions when Pt is replaced by Ni. The variation of γ along the series indicates a maximum around x = 0.9 which corresponds to the magnetic instability. It is worth noting that below T_c in the ferromagnetic compounds, C_mag follows a T law, characteristic of magnon dispersion.