Elmer E. Anderson

Antiferromagnetism and Electrical Transport Properties of Chromium‐Aluminum Alloys

Electrical resistivity ρ of Cr–Al alloys containing 0.3‐, 1.2‐, 1.9‐, 3.7‐, and 6.2‐at.% Al has been studied as a function temperature. The onset of antiferromagnetism causes small anomalies in the ρ vs T curves from which the Neel temperature TN can be determined. TN decreases rapidly with additions of small amounts of Al and then increases with larger Al concentrations. A minimum in the TN vs Al content curve occurs at about 1.2‐at.% Al. This minimum results from the fact that below about 1.5‐at.% Al level, the Cr–Al alloys possess an incommensurable antiferromagnetic structure. Above this concentration, the antiferromagnetic phase is of the commensurable type. The absolute thermoelectric power measurements on alloys containing 0.3 and 1.2‐at.% Al support the determinations of TN from the electrical resistivity studies.

ELECTRICAL RESISTIVITY AND THERMOELECTRIC POWER OF POLYCRYSTALLINE URANIUM AT ELEVATED TEMPERATURES.

The electrical resistivity, ϱ(T), of high purity uranium [ϱ(3.67 °K) = 0.955 μΩcm] has been studied as a function of temperature, T, between 295 and 1370 °K. Measurements also have been made on the absolute thermoelectric power, Su(T), between 380 and 1000 °K. The uranium used in this study is the same as that previously studied between 2 and 300 °K. The crystal structure changes taking place at elevated temperatures cause anomalies in the ϱ(T) vs. T and Su(T) vs. T curves. The agreement between the ϱ(T) data of different investigators is better for the α phase than for the β and γ phases. Large disagreements in Su(T) among different investigations exist at elevated temperatures. The Su(T) vs. T curve of the present study joins smoothly the curve between 20 and 300 °K due to Meaden and Lee. The abovementioned electrical transport properties are briefly discussed from the viewpoint of the electronic structure of uranium and the multiband conduction theory.

Critical exponent β for nickel and nickel-copper alloys

Abstract A linear extrapolation of the plot of the square of the applied magnetic field versus break-point temperature is shown to lead to an erroneous Curie temperature, which, in turn, can result in two values of the critical exponent β. Careful determinations of Curie temperatures result in a value for β of about 0.34 for nickel and nickel-copper alloys.

Antiferromagnetism and Electrical Resistivity of Chromium Alloys Containing Ruthenium and Osmium

Electrical resistivity ρ has been studied as a function of temperature T of chromium alloys containing 0.9, 2.1, 3.0, and 4.8 at.% Ru and 0.3, 0.6, 1.1, and 2.0 at.% Os. The onset of antiferromagnetism causes large anomalies in the ρ vs T curve. The Neel temperatures TN of both alloy systems increase rapidly with increasing solute concentrations up to 2 at.%, remain approximately constant, and then decrease with larger solute contents. The initial increase in TN with increasing solute concentration can be understood by Fedders and Martins theory assuming that additions of Ru and Os to Cr cause an increase in the electron jack and a decrease in the hole octahedron which enlarge the interaction area of the two Fermi surfaces. The incommensurable antiferromagnetic structure in both alloy systems exists up to about 0.5 at.%. For higher concentrations the antiferromagnetic phase, bordering the paramagnetic region, is commensurable with the lattice. The large increases in the electrical resistivity of the comm...

Electrical resistivity of chromium-ruthenium alloys☆

Abstract Electrical resistivity, ρ, has been studied as a function of temperature, T, for chromium alloys containing 6.6, 8.3, 10.1, 11.4 and 14.0 at.% ruthenium. The onset of antiferromagnetism causes large anomalies in the ρ vsT curves. The Neel temperature, TN which is the temperature at which dρ dT is a minimum, has been calculated for the above samples and also for the chromium-ruthenium alloys studied earlier. The Neel temperature is seen to increase rapidly up to the 3.0 at.% level, remain approximately constant for several percent, and then decrease with increasing solute content. The behavior of TN with ruthenium content and the general features of the ρ vs. T curves can be approximately understood from the viewpoint of the electron and hole Fermi surfaces of chromium and their changes as the electron concentration is increased.

Electrical resistivity of nickel-rich nickel-chromium alloys between 4 and 300 K

Electrical resistivity ρ of Ni−Cr alloys containing 5.5, 11.3, 15.7, 16.8, 19.4, 22.0, 24.6, and 27.0 at % Cr has been measured as a function of the absolute temperatureT between 4 and 300 K. The sample with the Cr content of 22.0 at % exhibits a small ρ minimum at about 10 K. No minimum has been observed in any other of the above samples, although an anomalousT dependence has been found in alloys containing 15.7, 16.8, and 19.4 at % Cr. The ρ minimum has been discussed from the viewpoint of the Béal-Monod theory for the Kondo effect in concentrated systems and the mechanism by Greig and Rowlands based on aT-dependent decrease of the impurity electrical resistivity. It is concluded that the ρ minimum in the Ni−Cr system is still a phenomenon which is not well understood at the present time.

SEEBECK COEFFICIENT OF BINARY CHROMIUM ALLOYS CONTAINING MOLYBDENUM OR TUNGSTEN.

Abstract The Seebeck coefficient (ifS) of Cr alloys containing 0.6, 3.2, 5.1, 6.9, 8.8 at.% Mo or 0.3, 0.7, 1.0, 3.4 at.% W has been measured as a function of temperature (T) between 50 ° and 350 °K. The Svs.T curves show large anomalies (increases in S) in this temperature range due to the transition from the paramagnetic to the antiferromagnetic state, made up of transverse spin density waves incommensurable with the chromium lattice. In the paramagnetic region Cr-Mo alloys approximately obey the Nordheim-Gorter rule. The Cr-W alloys do not obey this relation because of the anomalous behavior of the electrical resistivity with respect to the composition in the paramagnetic state. The increase in S, due to the onset of the antiferromagnetic state, can be approximately correlated with the increase in the electrical resistivity in Cr-W alloys. The Cr-Mo solid solutions show more complicated behavior.

Absolute thermoelectric power of chromium-ruthenium alloys

Abstract The absolute thermoelectric power ( S ) of chromium and chromium alloys containing 0.9, 2.1, 3.0, 4.8, and 8.3 at.% ruthenium has been determined as a function of temperature ( T ) between 350 and 1000 K. The S vs . T curves exhibit large anomalies in this temperature range due to the change from a paramagnetic to an antiferromagnetic state. The relative size of the anomaly increases with increasing ruthenium concentrations up to the 3.0 at.% sample. For higher concentrations, the anomalous effect becomes smaller with an increase in solute concentration. The large increases in the thermopower with decreasing temperatures in the antiferromagnetic region can be approximately correlated with the corresponding rise in the electrical resistivity curves. The CrRu alloy system is found to violate the Nordheim-Gorter rule.

Magnetic properties of Cr containing dilute concentrations of Co in the neighborhood of the Néel temperature

Magnetic susceptibility (χ) of Cr and Cr alloys continaing 1.7, 2.2, 2.7, 4.4 and 6.2 at.% Co have been measured as a function of temperature (T) between 300 and 600 K. Each of the χ vs T curves exhibits a well‐defined maximum at the Neel temperature (TN). Assuming that χ of the matrix is unchanged by small additions of solute, the magnetic susceptibility of Co (χCo) in Cr has been determined over the above‐mentioned T range. Above TN (except close to TN) χCo obeys the Curie‐Weiss law. The magnetic moment per Co atom decreased with increasing Co concentration. It has been found the χCo just above TN cannot be described by a power law with constant critical exponents.

Electrical resistivity and antiferromagnetism of chromium-platinum alloys

Abstract Electrical resistivity, ϱ, has been measured as a function of temperature, T, of Cr alloys containing 0.47, 0.93, and 1.63 at.% Pt. The onset of antiferromagnetism causes anomalies in the ϱ vs T curves which increase with increasing Pt concentrations. Using the criterion that at the Neel temperature, TN, dϱ/dT is minimum, it has been determined that the values of TN are (430 ± 10)K, (490 ± 5)K, and (535 ± 5)K for the above-mentioned alloys. The nature of the antiferromagnetic state and the corresponding anomalies in the electrical resistivity in the Cr-Pt system are very similar to those found in Cr-Ir solid solutions.