| Magnetic clusters play an irreplaceable role in various fields such as magnetic recording,biomedical treatment,and microwave absorption,so it is essential to make some research for magnetic cluster in aspect of cluster science.In the system of magnetic cluster,the magnetism of cluster is affected by some features of cluster,such as complex structure,multiphase composition and various magnetic coupling effect between the particles.The magnetic coupling can lead to various magnetic ordering phenomena,which are critical for next-generation nanoscale magnetic and electronic devices.In addition,the tunnel magnetoresistance of magnetic materials has broad application prospects.For example,the magnetic tunnel junction with spin-dependent Coulomb blocking effect is used as magnetic read head or magnetic sensor.It can enhance the output signal,improve the signal-to-noise ratio,and reduce the bit error rate.However,the spin-related transport mechanism in magnetic materials remains unclear.Therefore,the research of the transport properties in the magnetic clusters is also of great significance.In this paper,ferromagnetic cluster arrays with different parameters were prepared by cluster beam deposition.The morphologies of ferromagnetic cluster arrays were characterized with transmission electron microscope(TEM).The magnetic coupling and transport properties of ferromagnetic cluster arrays were also discussed.By controlling the flow rate of the buffer gas,the particle size of the Fe cluster arrays is in the range from 7.8 nm to 15.9 nm.It is found that the coercive force increases dramatically with the increase of the particle size,and the magnetization decreased with the appearance of the spin glass.Fe cluster arrays with different coverages were obtained by controlling the deposition time.With the increase ofcoverage,aggregations occur among most of the clusters and the coupling between particles is enhanced with the decrease of the spacing.Dense arrays of Fe-Cr alloy clusters with different Cr ratios were fabricated by cluster beam deposition.A lattice mismatched tetragonal-like morphology of the Fe-Cr alloy cluster was observed at large Cr ratio.The tetragonal-like structure of cluster exhibits the behavior of spin glass,which not only increases the degree of bifurcation of ZFC and FC curve,but also improves the anisotropy and thermal stability of Fe-Cr alloy clusters system.The transport properties of ferromagnetic spins were also discussed in this paper.Fe clusters arrays exhibit spin-dependent Coulomb blocking effect at low temperatures,and the threshold voltage is 18.3 V,which is much larger than the threshold voltage of nonmagnetic cluster arrays.The conductance versus temperature curve exhibits a three-stage transport process with temperature changes.Fe clusters arrays show the thermal-activated tunneling at high temperature,and the Variable range Hopping(VRH)at low temperature,and there is a significant transition in the intermediate temperature range.In addition,it is found that Fe cluster arrays show 80%giant magnetoresistance at low temperatures.By comparing the magnetoresistance of samples with different coverages,it is verified that the transport mechanism under the added field condition is high-order cotunneling.Moreover,positive magnetoresistance effect at low temperatures is also observed in the experimental results. |
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