engleski

Blocking of magnetic nano-clusters in Hf-Fe system

The hafnium-iron amorphous system Hf_{; ; 100− x}; ; Fe_{; ; x}; ; changes from nonmagnetic for x < 30 to magnetic for x ≥ 50. The range of x between these two regimes is of special interest (For x = 43 it was found that the nanometer sized magnetic clusters relax their magnetization thermally over the anisotropy energy barriers, D.Pajic et.al., J.Phys.:Condens.Matter 19(2007)296207 ). Here we investigated in more details the magnetic moment blocking phenomena for x = 35, 40, 43 alloys. The splitting between the measured zero field cooled and field cooled magnetization curves below the so called blocking temperature shows the characteristics of superparamagnetic systems. The magnetic field dependence of blocking temperature for Hf_{; ; 57}; ; Fe_{; ; 43}; ; is logarithmic in wide range of fields. This could be explained within the distribution of energy barrier heights similarly as the exponential temperature dependence of coercive field was explained. For Hf_{; ; 60}; ; Fe_{; ; 40}; ; the behaviour is more complex with two ranges of different logarithmic dependences. For Hf_{; ; 65}; ; Fe_{; ; 35}; ; the blocking temperature is below 2K, which is caused by the lower magnetic anisotropy and decreased cluster sizes due to the lower iron concentration.

magnetic nano-clusters ; amorphous alloy ; magnetic moment blocking ; magnetic anisotropy ; hysteresis

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