Indirect Exchange Interaction Among Gd in GdBa2(Cu1-xMx)3Oy (M = Ni, Co)
The specific heat of GdBa2(CU1-xMx)3Oy (M=Ni,Co) compounds was measured. Decrease of TN is observed with in-creasing x, however, it is larger in Ni substituted samples than in Co substituted ones. Ni-substituted samples at about 4 K have less value of entropy than samples of x=0, while Co concentration dependence of entropy is small in the Co-substituted samples. The effects of these substitutions on interactions among and to Gd ions are discussed.
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