Spin glass behavior and magnetocaloric effect in amorphous alloys Ce2 Fe23-x Mnx B3

The magnetic properties and magnetocaloric effect of amorphous alloys Ce2 Fe23-x Mnx B3 (1x6) were investigated. The magnetic properties are sensitive to the composition. For samples with x3, the low fraction and isolated Fe-Mn antiferromagnetic (AFM) coupling simply align antiparallel to the majority ferromagnetic (FM) order and reduce the total magnetization but cause no noncollinearity; thus they are typical FM materials with TC decreasing drastically from 336 to 226 K and the magnetization has a sharp drop around respective TC without thermal hysteresis suggesting a second order phase transition resulting from their amorphous nature. For x=4 and 5, amorphous alloys Ce2 Fe23-x Mnx B3 experience two transitions: first a paramagnetic (PM)-FM second transition at 143 and 81 K, respectively, and then a FM-spin glass (SG) transition. A PM-SG transition occurs at the freezing temperature (Tf) about 28.2 K for x=6. The SG behavior in amorphous alloy Ce2 Fe23-x Mnx B3 can be attributed to the disordered structure resulting from their amorphous nature and the competition between the Fe-Fe FM coupling and Fe-Mn AFM negative coupling. The magnetic entropy change for alloys Ce2 Fe23-x Mnx B3 with x3 is calculated using the Maxwell relation.