Interfacial exchange pinning in amorphous iron-boron nanoparticles -: art. no. 212401

Core-shell exchange pinning has been found at the interface between surface crystallites of antiferromagnetic goethite (alpha-FeOOH) and ferrihydrite (Fe(5)HO(8).4H(2)O) and 22 nm sized nanoparticles of a soft amorphous ferromagnet (Fe(69)B(31)). The pinning accounts for an unusually large coercivity and small saturation magnetization ( H(c)=165 Oe, sigma(s)=136 emu/g, at 10 K) in the nanoparticles, compared to melt-spun ribbons ( H(c)=60 mOe, sigma(s)=186 emu/g). It also explains field-cooled and zero-field-cooled thermomagnetization data in which peaks are observed in both curves at 150-200 K in applied fields of 200-1000 Oe; and the absence of an exchange bias effect, due to the lack of net coupling of the core and shell.