The Magnetic Properties Of 1111-Type Diluted Magnetic Semiconductor (La1-Xbax)(Zn1-Xmnx )Aso In The Low Doping Regime

We investigated the magnetic properties of (La1-xBax)(Zn1-xMnx)AsO with x varying from 0.005 to 0.05 at an external magnetic field of 1000 Oe. For doping levels of x <= 0.01, the system remains paramagnetic down to the lowest measurable temperature of 2 K. Only when the doping level increases to x = 0.02 does the ferromagnetic ordering appear. Our analysis indicates that antiferromagnetic exchange interactions dominate for x <= 0.01, as shown by the negative Weiss temperature fitted from the magnetization data. The Weiss temperature becomes positive, i.e., ferromagnetic coupling starts to dominate, for x >= 0.02. The Mn-Mn spin interaction parameter vertical bar 2 J/k(B)vertical bar is estimated to be in the order of 10 K for both x <= 0.01 (antiferromagnetic ordered state) and x >= 0.02 (ferromagnetic ordered state). Our results unequivocally demonstrate the competition between ferromagnetic and antiferromagnetic exchange interactions in carrier-mediated ferromagnetic systems.