Hi!
I met a problem about Ti/Al/Ni film. This film is used to form ohmic electrode to n-GaN. The question is: can this film become ferromagnetic when I measure the carrier concentration through Hall effect at low temperature? The film has been annealed at 850 centigrade, the time period is 30 period. Thanks!

Mainly replying because I'd like to hear the answer if anyone has it. As a complete guess I'd say no for the film alone. Although whoever answers might want a more precise definition of 'low temperature'.

Maybe this helps a bit...

When Ni films are grown by autocatalysis on steel or others, they are ferromagnetic unless their phosphorus concentration exceeds 13%.
Not exactly your situation... I'm speaking about 5µm thickness made in a liquid containing phosphates.

Basically, massive pure Ni is ferromagnetic, and thin film often magnetize spontaneously, despite annealed Ni having rather soft magnetic properties.

Did I understand properly that Ti is to react with the semiconductor, Ni is the barrier to diffusion and Al the thickest and farthest away from GaN?

Hoping you get information that better fits GaN technology!

OK, I googled a bit, not much information running around.

My guess was wrong, ohmic contacts on N-GaN use Ti-Al-Ni and then a good conductor like Au. Processes haven't gotten simpler over time.

What I saw was just that P-GaN becomes ferromagnetic when doped with Mn and maybe N.

Thank all.
I have to say that Al(200nm) film is on the top of Ti(20nm) film and Ni film is the toppest one. The reason why I want to know whether this alloy will become ferromagnetic under low temperature is that I wonder this electrode may form a ferromagnetic one, which may prove to be very helpful in GaN-based spintronics. I will try to low the temperature to see whether this process will happen or not.

Thank all.
I have to say that Al(200nm) film is on the top of Ti(20nm) film and Ni film is the most top one, that is this film is the farthest away from the GaN. The reason why I want to know whether this alloy will become ferromagnetic under low temperature is that I wonder this electrode may form a ferromagnetic one, which may prove to be very helpful in GaN-based spintronics. I will try to low the temperature to see whether this process will happen or not.

Well, if this alloy doesn't become ferromagnetic, you will find many that do. For instance the one used in magnetoresistive sensors.
www.zetex.com/3.0/appnotes/apps/an20.pdf simply uses Permalloy.

To see if you nickel is ferromagnetic, you may cross it with another (nonmagnetic) line that creates and measures magnetic fields. You put a nice sinus current in that line and look after peaks (at the times Ni isn't saturated) in the voltage.

It works very well in antitheft magnetic stripes. They give a nice powerful signal at 10kHz. One should only be sure to overshadow the Earth's magnetic field. And with the small cross-section of Ni you probably have, a higher frequency should be better. Antitheft stripes are typically 1mm*10µm in section, so your 1µm*200nm (?) could give as strong a signal at 500MHz; At 10MHz, you would see the peaks with a spectrum analyzer.

Of course, if you can make a conductive winding around a Ni torus, it will give you the complete B-H curve.

OK, I stop here, you probably have every measurement tool you need.