Synthesis and characterization of Ni–Cu alloy nanoparticles with a tunable Curie temperature

• Straightforward so-gel synthesis of homogeneous Ni–Cu alloy nanoparticles.
• Narrow particle size distribution and controlled Curie point.
• Applications in “self-regulating magnetic fluid hyperthermia”.
• Heating efficiency of nanoparticles as a function of composition and size.

A series of nickel–copper alloy magnetic nanoparticles with a range of Curie points from 51 °C to 63 °C were prepared by the reduction of intimately mixed nickel and copper oxides in a silica matrix using the sol–gel method. The silica matrix was subsequently removed with an etching solution, assisted by sonication. The alloy nanoparticles were characterized using X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA/SDTA), thermomagnetic analysis (TMA), transmission electron microscopy (TEM), magnetic measurements (SQUID, vibrating-sample magnetometer) and specific absorption rate measurements (SAR). The synthesized nanoparticles show a size in the range 15–20 nm, exhibited superparamagnetic behavior with a blocking temperature (TB) of approximately 135 K and a room-temperature magnetization of 3–9 emu/g, depending on the composition. The nanoparticles showed a relatively high effective anisotropy constant (Keff) and a significant heating ability in an alternating magnetic field. The synthesis method is straightforward and allows the preparation of homogeneous Ni–Cu alloy nanoparticles with a relatively narrow particle size distribution.

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