`Fe_(3)O_(4)` is ferrimagnetic at room temperature but at 850K it becomes::

Options

A. diamagnetic
B. ferrimagnetic
C. paramagnetic
D. anti-ferromagnetic

Answer

To solve the question regarding the behavior of `Fe_(3)O_(4)` at different temperatures, we will follow these steps:

### Step 1: Understand the Terms
- **Ferrimagnetic**: A type of magnetism where magnetic moments of atoms on different sublattices are opposed but unequal, resulting in a net magnetization.
- **Paramagnetic**: A state where materials have unpaired electrons and exhibit magnetism only in the presence of an external magnetic field. The magnetic moments are randomly oriented without an external field.

### Step 2: Analyze the Behavior at Room Temperature
- At room temperature, `Fe_(3)O_(4)` exhibits ferrimagnetic properties. This means that the magnetic moments are aligned in opposite directions but are unequal, leading to a net magnetic moment.

### Step 3: Consider the Effect of Temperature
- As temperature increases, thermal energy disrupts the alignment of magnetic moments. In ferrimagnetic materials, this disruption can lead to a change in magnetic behavior.

### Step 4: Determine the Behavior at 850 K
- At high temperatures, such as 850 K, the thermal agitation is sufficient to overcome the interactions that maintain the ferrimagnetic state. Consequently, the spins become more disordered.
- In this disordered state, the material behaves like a paramagnet, where the magnetic moments are no longer aligned and can only respond to an external magnetic field.

### Conclusion
- Therefore, `Fe_(3)O_(4)` transitions from being ferrimagnetic at room temperature to paramagnetic at 850 K.

### Final Answer
- The correct answer is: **Paramagnetic**.

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