Spin-disorder Resistivity Research Articles

Spin-disorder resistivity in the paramagnetic state of the heavy rare-earth dihydrides.

We present systematic measurements of the paramagnetic spin-disorder resistivity ${\ensuremath{\rho}}_{m}$ in Gd, Tb, Dy, Ho, and Er dihydrides. We observe that ${\ensuremath{\rho}}_{m}$ is strongly affected by crystalline-field effects especially as concerns ${\mathrm{DyH}}_{2}$ and ${\mathrm{ErH}}_{2}$. The absolute values of ${\ensuremath{\rho}}_{m}$ are much smaller than in the corresponding pure metals, an effect which can be attributed in part to modifications, with hydrogen, of the electronic band structure, but it implies also a reduction of the fundamental exchange interaction between conduction and localized electron spins.

Electronic structure and magnetic, electrical and optical properties of ferromagnetic Heusler alloys

Measurements of the electrical resistivity and the Hall effect of the Heusler alloys NiMnSb, PtMnSb, CoMnSb, AuMnSb, CuMnSb and PtMnSn are reported. The anomalous Hall effect is analyzed in terms of the contributions from skew scattering and side jump. The spin polarization of the charge carriers is proportional to the magnetization. This is an indication that the electronic structure as a function of the temperature is best described by a local band model, with complete spin polarization of charge carriers parallel to the local magnetization at all temperatures. The spin disorder resistivity of NiMnSb is calculated with the local band model. The magneto-optical Kerr effect of PtMnSb is enhanced by the plasma resonance of the charge carriers.

Observations of magnetic and structural ordering in TbH2+x compounds through electrical resistivity measurements.

We present detailed resistivity measurements rho(T) in the magnetically ordered state of TbH/sub 2+//sub x/. Three types of behavior are observed: (i) for xapprox. =0, we find a classical antiferromagnetic transition with a well-defined drop of the spin-disorder resistivity below T/sub N/approx. =18 K; (ii) for x>0, the total resistivity rho(T) goes progressively through a minimum and a maximum with decreasing temperature, indicating an incommensurate type of ordering which starts at temperatures above T/sub N/; (iii) for xgreater than or equal to0.15 and for samples presenting a structural transition within the H sublattice, we observe a sharp transition at 38 K, with a smoother minimum at about 55 K. These results can be at- tributed to modifications of the electronic structure and of the mean free path with x, and to the existence of uniaxial crystalline field effects related to structural short-range and long-range order in the H sublattice.

Electrical resistivity for thes-fmodel within the alloy analogy approximation (CPA)

The spin disorder resistivity for thes-f Hamiltonian with an additional Coulomb interaction between conduction electrons is calculated. The many body Hamiltonian is replaced by a four component alloy-Hamiltonian with temperatureT- and band-fillingn-dependent concentrations of the constituents. A self-consistent CPA-theory for conductivity and spin disorder resistivity is applied and numerically evaluated for different temperatures and parameters of the model Hamiltonian. Analytical formulae for the spin disorder resistivity are derived for two limiting cases. These results exhibit a strong dependence on the band-fillingn and the structure of the Bloch density of states near the chemical potential μ. A comparison with other theories and experimental data is presented.

Low-temperature specific heat measurements for Er and α-ErHx

The heat capacity of polycrystalline Er and alpha -ErHx solid solutions (0<or=x<or=0.03) has been measured between 1.5 and 70 K. The authors report a detailed analysis of the specific heat of pure Er, including a comparison with the literature data, which conflict widely. They observe that the antiferromagnetic (TN) and helicoidal (TH) transition temperatures decrease while the Curie temperatures TC and TC1 (for the change to commensurate structure) increase with growing H or D content, in agreement with what is found from magnetic and resistivity measurements. The hydrogenated specimens exhibit an increasing electronic contribution to the heat capacity; from the variation of the Neel temperature, the spin-disorder resistivity and the magnetic contribution to the specific heat they conclude that the exchange interaction reduces with growing H content.

Spin Disorder Resistivity and Bare Curie Temperature in the Ferromagnetic Superconductor ErRh4B4

Low temperature AC magnetoresistance measurements on a single crystal of ErRh4B4 were made to determine the bare Curie temperature and the spin disorder resistivity. A `crossed field' technique was used to suppress the superconductivity in order to probe the normal state properties. The bare Curie temperature was found to be 1.07K and the spin disorder resistivity extrapolates to a finite value at T=0K.

Spin-disorder resistivity and crystalline field effects in TmH2.

An analysis of the electrical resistivity \ensuremath{\rho}(T) of ${\mathrm{TmH}}_{2}$ yields the spin-disorder resistivity ${\ensuremath{\rho}}_{m}$ and its temperature dependence. ${\ensuremath{\rho}}_{m}$ is constant at high temperatures (${\ensuremath{\rho}}_{m}$=2.8 \ensuremath{\mu}\ensuremath{\Omega} cm, a value which is much smaller than for pure Tm); at low temperatures, ${\ensuremath{\rho}}_{m}$(T) decreases and tends to zero. This result can be interpreted on the basis of a nonmagnetic ground state separated from the first excited state by a gap of 150 K.

Magnetic properties and electrical resistivity of (Gd xLa 1- x)Ni, (0⩽ x⩽1)

The pseudobinary system (Gd, La)Ni shows the orthorhombic CrB-type of structure. Long-range ferromagnetic order exists for concentrations 0.3⩽ x⩽1.0. Almost constant values of μ eff/Gd and μ s/Gd are obtained for the whole system (except the increase of μ s for x=0.1 and 0.2). The concentration dependence of spin disorder resistivity is found to vary as ϱ spd ∝ x n (1+ Jx) with n≈3, which is not in agreement with the theory.

Magnetoresistivity in single crystal ErRh4B4

The magnetoresistance of single-crystal ErRh_4B_4 has been measured from 0.05 to 10 K with magnetic fields from 0 to 5 T applied along the magnetically easy a direction. The spin disorder resistivity in the normal state is interpreted with a crystal field model which also fits the magnetic anisotropy and specific heat. The data show that substantial spin disorder remains in ErRh_4B_4 even at T = 0 K in the ferromagnetic state.

Anisotropy and magnetic order effects on the Europium resistivity

We introduce and magnetic order effects, into the Kim's approach to the spin disorder resistivity, in order to discuss the Eu spin-only resistivity.

Structural dependence of the spin-disorder resistivity of thin dysprosium films

An increase of the spin-disorder resistivity with decreasing film thickness has been observed in dysprosium films of thickness below ≈ 120 nm. X-ray diffraction experiments revealed this dependence is caused by a structural change.

Transport properties of uranium monochalcogenide and monopnictide single crystals

The temperature dependence of the electrical resistivity and the Hall resistivity in magnetic fields up to 100 kOe is reported for US, USe, UTe, UP, UAs, and USb single crystals. The temperatures of the various first- and second-order magnetic phase transitions are derived as singularities in $\ensuremath{\rho}(T)$ and $\frac{d\ensuremath{\rho}(T)}{\mathrm{dT}}$, respectively. The magnetic part of the resistivity of the uranium monochalcogenides ($\mathrm{U}X$) is proportional to ${T}^{2}\mathrm{exp}(\frac{\ensuremath{-}\ensuremath{\Delta}}{{k}_{B}T})$, as expected for electron-magnon scattering. The value of the spin-disorder resistivity of all $\mathrm{U}X$ compounds can be interpreted with the same exchange integral. In UTe and USb, a logarithmic decrease of $\ensuremath{\rho}(T)$, known as the Kondo anomaly, is observed for $Tg{T}_{C,N}$. This behavior is discussed in the framework of existing theories and experiments on intermediate-valence and dense Kondo systems. Thus, the ferromagnetic ordering of UTe at 102 K is a new high ${T}_{C}$ for a Kondo material.

Intermediate valence behavior of ternary cerium and uranium transition metal borides

Low-temperature specific heat, electrical resistivity, ac magnetic susceptibility, and dc magnetization measurements were made on ternary cerium and uranium transition metal borides with the general formula CeT3B2 (T=Co, Ru, Rh, and Ir) and UT3B2 (T=Co, Ru, and Ir). The compound CeRu3B2 was found to exhibit superconductivity below 0.68 K. The values of the electronic specific heat coefficient range from 9.7 mJ/mole-K2 for CeCo3B2 to 64 mJ/mole-K2 for UIr3B2. The electrical resistivity versus temperature curves of all of the compounds exhibit negative curvature and are reminiscent of valence fluctuation behavior. In the case of CeIr3B2, the electrical resistivity attains a maximum value at 180 K, while the dc magnetic susceptibility has a temperature dependence that is typical of intermediate valence Ce compounds, approaching a finite value at zero temperature. The electrical resistivity of the ferromagnetic compound CeRh3B2 reveals a rapid decrease in spin disorder resistivity below 120 K. The dc magnetic susceptibility of this material can be described as the sum of a constant term and a Curie-Weiss contribution with an effective magnetic moment of 1.01 µB per formula unit and a Curie-Weiss temperature of 119 K. Magnetization measurements on CeRh3B2 yield a saturation magnetic moment of 0.37 µB per formula unit and a Curie temperature of 113 K.

Anomalous behavior of the spin disorder resistivity of (La,RE)Sn3

The temperature dependence of the spin disorder resistivity in dilute alloys of La1−xRExSn3 has been measured for RE=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er with x&amp;lt;0.10 and 1.5&amp;lt;T&amp;lt;300 K. The scaling of the high temperature incremental resistivity per rare-earth ion, Δρ/Δx, versus rare-earth atomic number is anomalous when compared to the variation typically seen in rare earth alloys and intermetallic systems. This quantity is larger for the lighter rare earths as compared to that measured for Gd and the heavier rare earths. For the lighter half of the RE series, the variation of the superconducting transition temperature depression rate ΔTs/Δx for (La,RE)Sn3 resembles the variation in Δρ/Δx. In addition, the temperature dependence of Δρ(T)/Δx for several rare-earth impurities is unusual. In particular, Δρ(T)/Δx for (La,Tb)Sn3 has a negative coefficient of resistivity at high temperatures with a maximum in the vicinity of 25 K. This anomalous temperature dependence can be accounted for by a first Born approximation calculation of the resistivity with the inclusion of both exchange and aspherical coulomb scattering in the presence of a crystalline electric field.

Thermal Conductivity and Electrical Resistivity of Ferromagnetic Intermetallic Compound ErNi

The thermal conductivity and the electrical resistivity of polycrystalline ErNi which is ferromagnetic below 10 K have been measured as a function of temperature between 1.5 and 15 K. The Lorenz function, calculated from the measured thermal conductivity and electrical resistivity values on the same sample, exceeded the value expected for electron heat conduction. This indicates that magnons significantly contribute to the heat conduction. The electrical resistivity below 3 K was proportional to T 1.9 ±0.3 which is due to spin-disorder resistivity.

The high temperature spin disorder resistivity of binary rare-earth alloys

Abstract The formula for the temperature spin disorder resistivity for the concentrated R 1− x R′ x Al 2 alloys is considered on the basis of CPA. The well-known Dekker formula is generalized. The comparison with experimental data for Gd 1− x Er x Al 2 is presented.

Influence of a random crystal electric field on magnetic susceptibility and electrical resistivity in Gd1-xRExAl2alloys

The magnetic and electrical properties of ferromagnetic Gd1-xRExAl2 alloys for RE=Tb, Dy, Ho and Er have been studied. The observed behaviour of magnetic susceptibility over the paramagnetic range and spin-disorder resistivity over the whole concentration range is anomalous and does not follow simple arguments. For x not=0 in the mixed alloys under investigation a curvature of 1/ chi versus temperature appears at about 700K due to the random Gd-RE ion substitution. The results suggest that lattice disordering occurs in this case.

Electrical resistivity and thermopower of amorphous FexCo80−xB20 alloys

A systematic study of the electrical resistivity ρ and thermopower S of amorphous FexCo80−xB20 alloys in the temperature range 4 K&amp;lt;T&amp;lt;300 K has been undertaken. The analysis of the resistivity data reveals that both s–d scattering and scattering by structural disorder contribute to ρ. From the structural contribution to ρ reasonable values of the Debye temperature θ (280–400 K) have been estimated. The physical significance of the variation of the spin-disorder resistivity with x has been discussed in terms of the spin-wave stiffness constant D and the s–d exchange integral Jsd. The calculation of 2kF values from the experimental data according to the outlined transport model explicitly shows its limitation. The thermopower S is not linear over any large range of temperature contrary to the prediction of a pure structural transport model. The thermal behavior and the variation of the room temperature values of S with x is similar to that observed in crystalline Fe–Ni alloys. It is argued that the extension of Kasuya’s relation based upon the s–d exchange interaction model should provide an approximate description of the temperature dependence S of ferromagnetic amorphous alloys.

A laboratory project on the electrical resistivity of ferromagnetic metals

The temperature dependence of the electrical resistivity of ferromagnetic metals such as iron or nickel is investigated in the ordered and paramagnetic regions. Contributions to the resistivity due to phonons and to the spin disorder that develop as the material is heated up are separated. The temperature dependence of the spin disorder resistivity can be described fairly well by a model in which the nearly free s electrons scatter from the localised d electrons.

Resistivity investigations in the Gd1-xErxAl2system

The electrical resistivity in the temperature range up to room temperature for the Gd1-xErxAl2 system has been investigated. The Curie temperature, Tc, spin-disorder resistivity, rho s, and residual resistivity, rho r, were determined. Anomalous behaviour of the spin-disorder resistivity versus Er concentration and correlation with the X-ray structural disordering investigations has been observed.