Magnetic and thermophysical properties of Gd_XMn_1−XS solid solutions

Abstract

The structural, magnetic, and thermophysical properties of cation-substituted sulfides Gd(X)Mn(1-X)S (0.04 ≤ X ≤ 0.25) with the NaCl-type face-centered cubic lattice have been investigated. The range of existence of long-range antiferromagnetic order has been established. The anomalies observed in the temperature dependence of the specific heat correspond to the temperatures of the magnetic phase transition. The anomaly in the specific heat caused by electron transitions between the 4f levels and d band states has been observed. It has been found that the coefficient of thermal expansion decreases with increasing concentration of substituents in the magnetically ordered region and remains nearly invariable in the paramagnetic phase.

Crystal Structure and Magnetic Properties of Mn1-xGdxSe Solid Solutions

“…If make a comparison of results of magnetic properties measurements which were carried out in this work with results of work [6], we can see that substitution of manganese ions by gadolinium ions in manganese selenide leads to more signicant changes of the magnetic characteristics, than in a Mn 1−x Gd x S system. For example, the Néel temperature for Mn 0.9 Gd 0.1 Se composition is equal to ≈100 K, and for Mn 0.9 Gd 0.1 S composition ≈120 K. This is due to the size factor of the anions.…”

Magnetotransport effects in paramagnetic Gd x Mn1 − x S

“…The orbital ordering in the Gd x Mn 1 -x S solid solu tion is confirmed by a broad peak in the specific heat at T = 380 K in the curve obtained by the subtraction of the phonon contribution from the measured tem perature dependence of the specific heat [9]. The dif ference in the values of the critical temperature obtained from the data on the specific heat and mag netoresistance results from the fact that the specific heat peak is related to the decay of the long range order, whereas the magnetoresistance is observed above the critical temperature and is determined by the short range orbital order and vanishes at higher temperatures.…”

“…The magnetic and calorimetric measure ments [9] revealed a decrease in the magnetic phase transition temperature from T = 150 K to T(x = 0.2) = 120 K and allowed determining the critical doping level corresponding to the decay of the long range order and to the formation of a spin glass (x c = 0.23). The measurements of electrical resistance were per formed by the four probe method in the applied mag netic field H = 0.8 T perpendicular to the electric cur rent.…”

“…3). This dependence has been obtained by the subtraction of the asymptotic continuation of the linear high temperature function ΔV/V [9] at T > 250 K from the total temperature dependence of the relative change in the sample volume. Below 250 K, the lattice starts to shrink and the electrical resistance increases.…”

“…At x = 0.1, the orbital polarons become pinned at T = 400 K and the magnetic moments of electrons form superparamagnetic parti cles. Similar to the spin systems, where the fluctua tions of spin density described in terms of a short range magnetic order lead to the displacement of the mobility edge and the growth of the electrical resis tance, here we use the short range order in the orbital subsystem, which is described by the correlation func tions of orbital magnetic moments [9] and modifies the width of the conduction band, [1 -〈L(0)L(r)〉]W. The electron ordering at certain orbitals leads to the anisotropy of hopping integrals and the narrowing of the conduction band, i.e., to an increase in the energy needed for the activation of charge carriers from the impurity level to the bottom of the conduction band. At low temperatures, the orbital magnetic moments of clusters are oriented chaotically and the correlation function 〈L(0)L(r)〉 tends to zero.…”