MOSFET IRF740 and 3,6 V
The threshold voltage is the minimum voltage required so that the transistor starts to conduct. And you need more than this to put it into saturation.

The Vth (threshold voltage) of the IRF 740 is min=2v, max=4v so definitely you're in unchartered territory. 

Moreover let's look at this graphic:


You need at least 4V to have 100mA (although with a 50V drain voltage).

To power off, specially since you might have ground planes I strongly believe it's better to use a P mosfet to cut the (+) side of the supply. The schematic would look something like this:



Control input is your microcontroller. This turns on/off a logic NMOS. When it's on the current passing is very little because it's limited by a 1Mohm resistor. 

While turned on it forces ground on the gate of the PMOS, thus, turning it on and allowing power.

When the control input is low, the NMOS is off. The 1Mohm resistor pulls up the gate of the PMOS and it's off. With this simple circuit you can control power to your loads. If your microcontroller will shutdown the pin and turn it off, make sure you put a pulldown to the pin so the NMOS stays off when the microcontroller pin is in High-Z while asleep.

Hope it helps