Stabilization of Reentrance AFM on Gd2Al System in a Certain Electron Concentration

Abstract

A random mixture of two compounds with different type of magnetic ordering which can lead to a new phase with different magnetic characteristics is studied. Such an interesting random magnetic system can be formed by a ferromagnet (e.g. Gd 2 Au) and antiferromagnetic system like e.g. Gd 2 Al with localized magnetic moments where, in principle, the dominant exchange interactions are those of the nearest neighbours. A systematic study on the solid solutions of the type Gd 2 (Al 1± ±x Au x ) is reported here. (I) The roles and effects of conduction electron concentration ªc.e.c.º on the magnetic structure, where the magnetic behaviour is shape dependent (0.2`x`0). (II) The cause of magnetic instability of Gd 2 Al, which should be due to the ªc.eº. (III) The critical stabilized point by decreasing ªc.e.c.º. It is shown that the magnetic phase of the pseudobinary intermetallic compound Gd 2 (Au x Al 1± ±x ) becomes unstable by increasing the conduction electron concentration through the variation in unit cell dimensions. It becomes stable at a critical value of c.e.c., where Se ij J ij 0, resulting in a paramagnetic behaviour (q p % 0 to 5) at x 0.3. It is shown that the instabilities of the crystal and magnetic structure are functions of c.e.c. and depend on the Fermi sphere K F which is the main cause of the shape dependence of the magnetic structure of the sample.

Dissipative heat and exchange dispersion on metastability of Gd5Si4

“…On the other hand, we are aware that the magnetic character of Gd is ferromagnetic (FM) with T c ¼ 298 K (even in high pressure) while in these isostructure compounds Gd 5 X 4 , the magnetic ordering is in two surprising limits T c ¼340 K for Gd 5 Si 4 and T N ¼15 and 53 K for Gd 5 Ge 4 [12,15]. Following our previous investigation of the meta-magnetic character with high m eff ¼9.6m b and low m eff ¼4.5m b effective magnetic moment [5,16,17], now the cause and the effect of these two limiting cases with high electrical resistivity in Gd 5 X 4 [15] are in a question. The high electrical resistivity is reported to be due to a large entropy change deduced from a change in FM (T c ¼340 K for Gd 5 Si 4 ) to antiferromagnetic (AFM) state (T N ¼15 K of Gd 5 Ge 4 ) [18].…”

“…The contribution of these electrons to magnetic ordering, which unequivalently links the magnetic structure to lattice parameter [5], offers a unique opportunity for investigating the origin of the magneto-crystalline character. The exchange fluctuation is known to be important in such systems [6,7] where it could be the consequence of the coupling of magnetic moments carried by either the ''localization'' or the ''itinerant'' electron [8,9].…”