Large Room Temperature Magnetic Moment in Mn ${_{1-x}}$ Zn ${x}$ Fe2O4 Thin Films for ${x \geq0.4 }$

Mn
${_{1-x}}$
Zn
_x
Fe
₂
O
₄
(
$0.1\le x\le 0.8$
) thin films with nanocrystalline grains were deposited on amorphous quartz substrate using pulsed laser ablation technique, at a substrate temperature of 650 °C. For
$x\le 0.3$
, the room temperature spontaneous magnetization (
$4\pi M_{S}$
) of thin films was observed to be lower than the bulk composition. For
$x=0.7$
, the room temperature
$4\pi M_{S}$
value (~6.1 kG) is 7.5 times the bulk value for same x. This value is only 1.4 times of the bulk at 10 K, signifying a large enhancement in the exchange constant for thin films. The exchange stiffness constant (D) values were evaluated by fitting the
$4\pi M_{S}$
data to the Bloch equation. The D values of thin films were always higher than that of the bulk. This result can be explained on the basis of occupancy of nonmagnetic Zn
²⁺
on both the tetrahedral (A) and octahedral (B) sites. This is unlike in the bulk, where all the Zn
²⁺
ions occupy only A site.