Low frequency low voltage Sine wave generator
To generate the sine wave, there are a few possibilities- AD9850 DDS modules are readily available, as are other DDS in chip form (you'll need a micro to set them up). 

A micro could be used directly, using DAC or PWM output. You would implement a sine lookup table.

A triangle wave oscillator is easy to make with a couple op-amps, the waveform can be flattened with diodes and resistors or JFETs (I don't recommend this old school method -too many parts- unless you have a real aversion to digital).

To actually drive the electromagnet, you probably need a power amplifier, and the details will depend on the current required. It could be just an op-amp, a high current op-amp, or perhaps something more substantial would be required. You might need +/-6V supplies (plus a low voltage digital supply) to generate a 3V RMS sine wave.