Neutron-Diffraction Studies on the Magnetic Ordering Process in the Layered Mn Perovskite La2-2xSr1+2xMn2O7(x=0.40,0.45and0.48)

Comprehensive neutron-diffraction studies on La 2-2 x Sr 1+2 x Mn 2 O 7 ( x =0.40,0.45 and 0.48) single crystals have revealed that the low-temperature magnetic phase consists of planar ferromagnetic (FM) and A-type antiferromagnetic (AFM) components, indicating a canted AFM ordering. Upon increasing the hole concentration x , the canting angle between planes changes from 6.3° (nearly planar FM) at x =0.40 to 180° (A-type AFM) at x =0.48, while the ordering temperature of the FM component, T C , decreases from 120 K to 0 K, correspondingly. We have also discovered that the A-type AFM ordering remains above T C and shows an anomalous exponential decrease to T N ∼200 K. This newly found intermediate A-type AFM phase may play a significant role in the enhancement of CMR effects in this layered Mn perovskite system.