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The effect of impurities on the magnetoelastic properties of Gd(sub 5)Si(sub 2.09)Ge(sub 1.91) system is reported through the measurement of thermal expansion. The results show that the impurities (mainly C, O, N, and F) in the Gd starting material alters the strain and Curie temperature of Gd(sub x)(Si(sub x)Ge(sub 1-x)) alloys.

Magnetic force microscope (MFM) with a heating-cooling stage was used for examining the magnetic-martensitic phase transformation of Gd5(Si(sub x)Ge(sub 1-x))4 (x ~ 0.5). Hysteresis in temperature was observed in the order-disorder transition and the ferromagnetic phase exhibited strong magnetic anisotropy.

[Gd.sub.5][([Si.sub.x][Ge.sub.1-x]).sub.4] has displayed a field induced first order phase transition from a monoclinic paramagnetic to an orthorhombic ferromagnetic at temperatures above its Curie temperature. The field induced first order phase transition is observed above the projected second order phase transition temperature of the orthorhombic phase, which is attributed to the fact that the applied field is so high that it causes the broadening to a wide range of higher temperatures of the second order phase transition of the orthorhombic phase.

[Gd.sub.5][([Si.sub.x][Ge.sub.1-x]).sub.4] for 0.41

The first order transition of a single crystal sample of Gd5(Si0.5Ge0.5)4 is verified with thermal expansion (TE) and magnetostriction (MS) measurements. The TE measurements indicate that the magnetic structural phase transition temperature was 259.5 K on cooling and 261.5 K on heating.

Magnetic relaxation measurements were used to examine the dynamics of the magnetic-structural phase transition in Gd5Ge2Si2. The energy barrier surmounted to affect the transformation of paramagnetic, half bonded monoclinic structure to the ferromagnetic, fully bonded orthorhombic structure was calculated to be 4.2 plusminus 0.2 eV.