What is the example of ohmic material?

Metals like copper, silver, gold, iron, etc are examples of ohmic metals.

There are very few ohmic materials. Ohmic materials are those that obey Ohm's Law, and very few do -which might come as a surprise to many people (Ohm's Law is NOT universal law!)! For a material to obey Ohm's Law, the ratio of voltage to current must remain constant for variations in voltage. Because increasing current causes increasing temperature, the resistance (and, therefore, the ratio of voltage to current) of most materials will change for variations in voltage.

So, an ohmic material must maintain an approximately-constant resistance over a wide range of temperatures -so metals such as copper, silver, gold, etc., do NOT qualify! However, alloys such as constantan (a nickel-copper allow) would qualify as being ohmic.