Effect of exchange bias on the electrical resistivity of Pd doped NiMn thin films: Two-channel Kondo system

Abstract

Electrical resistivity measurements have been carried out for both flash-evaporated reentrant spin glasses ͑RSGs͒ ͑Ni 76−x Pd x ͒Mn 24 and Ni 74.5 Mn 23.5 Pd 2 , as well as Ni 75 Mn 23 Pd 2 , a pure SG. These measurements were carried out at temperatures down to 4 K. We observed a very deep resistivity minimum at about 75 K for Ni 74 Mn 24 Pd 2 . It was found previously ͓Öner et al., J. Appl. Phys. 89, 7044 ͑2001͔͒ that this sample shows the largest coercivity and exchange unidirectional anisotropy among these films. In addition, magnetization measurements show that this takes place just on the border of the RSG such that it could be handled as a superparamagnetic sample. Previously it was assumed that the exchange bias created in the sample between the domains plays the dominant role in the resistivity minimum. On the other hand, in order to account for the temperature dependence of the resistivity below the minimum we have analyzed these data using the Kondo, two-channel Kondo, weak localization, and Cochrane models for structural disorder based on the Anderson mechanism. We have deduced that the two-channel Kondo model gives the best agreement with the data; a logarithmic temperature dependence ⌬ ͑T͒ = ␤ log 10 ͑T / T K ͒, was observed at the temperatures below T f accompanied by a resistivity behavior ⌬ ͑T͒ = 0m ͑0͒͑1−␣T 1/2 ͒, at lower temperatures. All parameters deduced from the fitting correlate consistently with the strength of the exchange anisotropy and coercivity in the RSG films, and thus provide a separate measure of the presence of antiferromagnetically coupled domains in these materials.

The study of thermal and electrical properties of Fe‐based amorphous alloys Fe80‐xCox P12B4Si4

“…At temperature lower than 80 K the expression provides a good description of the resistivity of all samples. The scattering from randomly positioned vibrating atoms gives a T 2 temperature dependence in the resistivity of amorphous ribbons [18]. It is found to be small in metalmetalloid films such as Ti-Co [19]; however, in Ni-P films this term can dominate [20], and one would expect a similar situation to hold in Fe-Co-based alloys, as indeed was found from our fitting procedure.…”

Structural and magnetic transitions in cubic Mn3Ga

“…Low-temperature resistivity minima, caused by the localized electron states in the random crystal potential of disordered alloys, have been reported in amorphous and disordered solids [22,28,29]. In these materials, the interaction of the itinerant electrons with the low-lying excitations gives rise to a resistance minimum (Kondo-like effect) [28].…”

“…As the temperature decreases below room temperature, the resistivity of the sample decreases almost linearly and passes through a minimum at 28 K. Below the minimum, the resistivity increases as a log function but deviates from its logarithmic behavior as the temperature decreases below 4 K, as shown in figure 9(b) and in the inset of figure 9(a). The data can be fitted to the expression ρ = ρ 0 − A ln(T 2 + δ 2 ), where A and δ are constants (see top-right inset of figure 9(b)) [22]. The interesting features of the resistivity are: (i) the samples show a positive temperature coefficient of resistance (metallic), but the residual resistance ratio (RRR) defined as R 300 K /R 4 K is very close to unity (RRR = 1.1), indicating that there is a substantial structural disorder in the samples.…”

Synthesis and magnetism of single-phase Mn-Ga films

“…If the low-temperature spin structure has spin-glass-like feature, the conduction electrons may exhibit scattering from a nearly degenerate two-level system as suggested in Ref. 16. This type of low-temperature resistivity behavior has been observed in other Mn-based magnetic alloys such as disordered cubic Mn 3 Ga. 11 Both samples show positive and small magnetoresistance (0.7% at room temperature).…”

“…4(c). 11,16 The values of the residual resistivity ratio (RRR) defined as q 305 K /q 2 K for the Mn 2 Ga 5 and Mn 3 Ga films are close to one, indicating that the films have substantial structural disorder which would produce spin disorder because of likely antiferromagnetic Mn-Mn interactions. If the low-temperature spin structure has spin-glass-like feature, the conduction electrons may exhibit scattering from a nearly degenerate two-level system as suggested in Ref.…”