Freezing Mechanism of Spins in Reentrant Spin-Glasses

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In order to shed light on the magnetism of reentrant spin-glasses, ac susceptibility, magnetization magnetic relaxation, field-cooling effect and Mossbauer spectroscopy on <^(57)Fe> have been investigated for the following alloy systems. (i) Polycrystalline <Fe_(100-x)> <Ni_x> (20<=x<=50) alloys, (ii) Single crystal <Fe_(65)> <Ni_(35)> alloy, (iii) Polycrystalline <(Fe_65Ni_35)_(1-x)(Fe_84Mn_16)_x> (0<=x<=0.26) alloys, (iv) Amorphous <(Fe_(1-x)M_x)_77> <Si_(10)> <B_(13)> (M=V,Cr,Mn,Co,Ni, 0<=x<=1) alloys, (v) Amorphous <Fe_(100-x)> <Sm_x> (17<=x<=72.5) and <Co_(100-x)> <Sm_x> (50<=x<=70) alloys.The obtained results are summarized as follows.(1) The magnetic phase diagram was determined for each alloy system described above. A spin-glass phase was observed in a certain composition range for each alloy system except <(Fe_(1-x)Co_x)_77Si_10B_13> amorphous alloy system.(2) The transition temperature <T_g> between spin-glass and ferromagnet depends strongly on the measuring magnetic field. … More Therefore, the spin-glasses transform into ferromagnet by applying a magnetic field exhibiting a hysteresis loop.(3) The average hyperfine field<H> obtained from analysis of the <^(57)Fe> Mossbauer spectrum exhibits a steeper increase below <T_g> for polycrystalline Fe-Ni-Mn and amorphous <(Fe_(1-x)Co_x)_77Si_10B_13> alloys, while does not for amorphous <Fe_(100-x)> <Sm_x> alloys. These results indicate that the freezing mechanism of spins in the Fe-Sm alloys is different from that in the Fe-Mn alloys.(4) Based on the experimental results the most essential factor leading to spin freezing is the competition between the ferromagnetic and antiferromagnetic interactions in the alloys.(5) The antiferromagnetic interaction in amorphous (Fe,Co)-Sm alloys is a exchange enhanced RKKY interaction caused by the crystal-induced J-mixing effects of <Sm^(3+)> .(6) The antiferromagnetic interaction in other alloy systems may arise from iron atoms which are surrounded by a lower number of iron atom. The lower coordination number causes a frustration of iron spins. Less