In an attempt to characterize the magnetic ordering in $\mathrm{Au}\mathrm{Fe}$ alloys, systematic studies were made of the temperature dependences of the thermoelectric power $S$ and the low-field magnetic susceptibility $\ensuremath{\chi}$ for Fe concentrations $C$ from 1 to 22 at.%. The concentration dependences of the magnitude and temperature of the maximum in $S(T)$ showed transitions clearly related to the magnetic ordering. Data analyses based on molecular field theories indicate the existence of small regions of short-range ferromagnetic order which undergo longrange interactions as the temperature is lowered. For $C\ensuremath{\gtrsim}12$ at.%, long-range ferromagnetism is dominant. Lower-concentration alloys ($C\ensuremath{\lesssim}12$ at.%) exhibit an antiferromagnetism with some properties similar to those of a magnetic spin-glass, but with well-defined ordering temperatures characterized by sharp cusps in $\ensuremath{\chi}(T)$, and with a negative Curie $\ensuremath{\theta}$ for $C=1 \mathrm{and} 2$ at.%. These properties indicate a more perfect antiferromagnetic order than that expected for a random alloy or a spin-glass, and this may be related to preferred local lattice arrangements in these alloys.

Magnetic Ordering in Gold-Iron Alloys

Publisher Summary This chapter discusses dilute transition metal alloys. The subject of dilute transition metal alloys may be divided into two classes of interest: (1) non-interacting or very dilute 3d-magnetic impurities dissolved in a non-magnetic host, which can be classified under the general heading of the Kondo effect—a localized antiferromagnetic interaction of the isolated impurity spins with the surrounding conduction electrons and (2) the impurity spin-spin interactions, which lead to giant moment ferromagnetism and spin glass freezing. These latter two cases represent different examples of magnetic ordering such as a long-range, but nonuniform, ferromagnetic alignment, and a random arrangement of frozen spin-orientations. Both of these effects depend strongly on the conduction electrons to propagate the magnetic interactions over large distances. The boundary between these two dissimilar states of magnetism is controlled by the magnetic behavior of these itinerant electrons. The chapter reviews the listing of alloy systems, experimental properties, and theory of random alloys.

Chapter 2 Dilute transition metal alloys; Spin glasses

Anisotropic thermopower of (TMTSF)2PF6: 1D–2D cross over and SDW ordering

Data on the magnetothermopower and specific heat of three compounds belonging to ``1111'' oxypnictides family are reported. One specimen $({\text{SmAsFeO}}_{0.8}{\text{F}}_{0.2})$ is a superconductor with ${T}_{c}=53\text{ }\text{K}$, while two others (SmAsFeO and NdAsFeO) are nonsuperconducting parent compounds. Our results confirm that spin-density-wave (SDW) order is present in SmAsFeO and NdAsFeO. In these two samples a strict connection between the thermoelectric power and electronic specific heat is found in the vicinity of SDW transition, which indicates that the chemical potential of charge carriers strongly depends on temperature in this region. Low-temperature data suggest presence of significant contribution magnon drag to the thermoelectric power.

Evidence of spin-density-wave order in R FeAsO 1 − x F x from measurements of thermoelectric power

Anomaly in the seebeck coefficient near the spin ordering temperature of magnetic metals

The Seebeck coefficient can be related to the specific heat of the charge carriers. Experiments on the itinerant ferromagnet nickel show that the specific heat determined from the Seebeck effect agrees closely with that determined from conventional specific-heat measurements.

S. H. Tang

Papers

Seebeck Coefficient at the Curie Temperature: Specific Heat of Charge Carriers in Ferromagnets