MAGNETIC FIELD EFFECT ON ENTROPIC DISORDERING IN SPINEL SPIN GLASS Ga0.8Fe0.2NiCrO4

Abstract

Mössbauer measurements [T (temperature) = 4.2–298 K (room temperature), H (external magnetic field) = 0, 0.25, 0.5, 2, 4, 12, 40 kOe], carried out in mixed spinel ferrite ( Ga x Fe 1-x)A [NiCr] B O 4 (x = 0.8), show the presence of pinned and entropic disorderings in this spin glass (SG) system, which is in agreement with the earlier studies. Magnetic hysteresis measurements (T = 4.2 K , H = 0-± 60 kOe ) too support this picture. The number of entropic spins in the lattice, N ES , deduced by the Mössbauer effect, is found to increase with decreasing T and decrease, rather sharply, with increasing H. These observations rule out any magnetic cluster formation by entropic spins, reveal their individual paramagnetic nature and confirm their origin in the existence of magnetically frustrated bonds in the lattice. These findings are in agreement with the predictions of the earlier developed Monte Carlo studies and cluster phase transition model.