Distant-neighbor exchange constants from magnetization steps inZn1−xCo

Abstract

Direct measurements of several exchange constants J;, for several neighbors located at different distances r;, are possible via the magnetization-steps method. Predictions for the distance dependence of the exchange constant can then be tested. The theory of the magnetization steps (MS's) caused by distant neighbors is presented. This theory is based on a sequence of cluster models. The problem of identifying the particular exchange constant J; that is responsible for an observed series of MS s is also discussed. The magnetization of Zn& "Co Te, with x =0. 007, was measured at 0.6 K in magnetic fields up to 27 T, and at 0.08 K in fields up to 20 T. Two series of MS's were observed. These series were identified as being due to pairs of next-nearest neighbors (J& pairs), and pairs of third neighbors (J3 pairs).The exchange constants deduced from the data are J2/k& = -(5.7+0.6) K and J3/k& = -(2.7+0.3) K. These values, and the earlier result J&/kz = -38 K for the nearest-neighbor exchange constant, are compared with several proposed dependences of J; on distance.

Eu-Eu exchange interaction and Eu distribution inPb1−xEuxTefrom magnetizatio

“…It is known that long range exchange interactions between further neighbors can influence the magnetization process in diluted magnetic semiconductors. 10,[20][21][22] Such long-range interactions may be important in smallgap DMS, such as the present system. The key question here is whether long-range interactions could have affected the magnetization in fields above 10 kOe significantly, since the conclusion of a non-random distribution was based on the data at these high fields, especially above 30 kOe.…”

“…10 Alternative approaches use more general spin clusters which include further neighbors within the clusters, so that the intracluster interactions already include the further neighbors. [20][21][22] Since our analysis started from the single-J model, the first approach (effective fields acting on the single-J clusters) is more convenient here. The effective fields from further neighbors slow down the alignment of spins which are singles, and they shift and broaden the ramps and MSTs arising from larger clusters (e.g.…”

Diluted Magnetic Semiconductors in High Magnetic Fields

“…Thus far J2 steps were observed only in Cobased DMS, in which the exchange interactions (including J2) are relatively strong [13,19]. There is, of course, no reason to stop at J2.…”

“…In this model both J1 and J2 are included but all other exchange interactions are ignored [13]. Such a model presupposes.…”

“…The first generation of MSTs succeeded in determining J1 in virtually all Mn-based II-VI DMS. More recently the technique has been extended along several lines: (1) the determination of J1 in some Cobased II-VI DMS (CdCoS and CdCoSe) using 60 T pulsed fields [11]; (2) studies of inequivalent NNs in the wurtzite stucture [12]; (3) determination of the smaller exchange constants J2 and J3 [13], and (4) observations of another type of MST, arising from isolated Co++ ions in wurtzite DMS [14].…”