What is the Difference Between Paramagnetic and Superparamagnetic

The key difference between paramagnetic and superparamagnetic is that magnetic susceptibility of a superparamagnetic material is larger compared to that of a paramagnetic material.

The term paramagnetic refers to some materials having weak attractions to externally applied magnetic fields where they internally have induced magnetic fields in the direction of the applied magnetic field. The term superparamagnetic, on the other hand, refers to the form of magnetism that appears in small ferromagnetic or ferrimagnetic nanoparticles.

Magnetic susceptibility refers to the measure of how much a material can become magnetized in an applied magnetic field. We can describe it as the ratio between the ratio of magnetization and applied magnetizing field intensity.

CONTENTS

1. Overview and Key Difference
2. What is Paramagnetic 
3. What is Superparamagnetic
4. Paramagnetic vs Superparamagnetic in Tabular Form
5. Summary – Paramagnetic vs Superparamagnetic 

What is Paramagnetic?

The term paramagnetic refers to some materials having weak attractions to externally applied magnetic fields where they internally have induced magnetic fields in the direction of the applied magnetic field. It is a form of magnetism, and other major forms include diamagnetic and ferromagnetic materials. Paramagnetic materials mostly include chemical elements and some compounds that have relative magnetic permeability that is slightly greater than 1. Therefore, these materials are attracted to magnetic fields.

Most atoms having incompletely filled atomic orbitals are paramagnetic because paramagnetism occurs due to the presence of unpaired electrons in the material. However, there can be some exceptions, such as copper. The spin of unpaired electrons tends to have a magnetic dipole moment, which makes them act like tiny magnets. Moreover, the spins of electrons align parallel to the magnetic field when an external magnetic field is present. This causes a net attraction.

However, paramagnets do not retain any magnetization in the absence of the external magnetic field because of the thermal motion that randomizes spin orientations. Therefore, total magnetization tends to drop to zero upon the removal of the applied magnetic field.

What is Superparamagnetic?

The term superparamagnetic refers to the form of magnetism that appears in small ferromagnetic or ferrimagnetic nanoparticles. It is also a form of magnetism. Typically, in small nanoparticles, magnetization can randomly flip the direction when there is an influence coming from temperature. We call the typical time between the two flips as the Neel relaxation time.

When there is no external magnetic field, the time that we use to measure the magnetization of the nanoparticles is much longer than the Neel relaxation time, so their magnetization appears as average zero. This state is called the superparamagnetic state. When this state occurs, an external magnetic field can magnetize the nanoparticles in a way similar to that of a paramagnet. In addition, the magnetic susceptibility of a superparamagnetic material is larger compared to that of a paramagnet.

What is the Difference Between Paramagnetic and Superparamagnetic?

Magnetic susceptibility refers to the measure of how much a material can become magnetized in an applied magnetic field. We can describe it as the ratio between the ratio of magnetization and the applied magnetizing field intensity. The key difference between paramagnetic and superparamagnetic is that the magnetic susceptibility of a superparamagnetic material is larger compared to that of a paramagnetic material.

The below infographic presents the differences between paramagnetic and superparamagnetic in tabular form for side by side comparison.

Summary – Paramagnetic vs Superparamagnetic

The term paramagnetic refers to some materials having weak attractions to externally applied magnetic fields where internally, they have induced magnetic fields in the direction of the applied magnetic field. The term superparamagnetic refers to the form of magnetism that appears in small ferromagnetic or ferrimagnetic nanoparticles. The key difference between paramagnetic and superparamagnetic is that the magnetic susceptibility of a superparamagnetic material is larger compared to that of a paramagnetic material.

Reference:

1. “Superparamagnetism.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Liquid oxygen in a magnet” By Bob Burk, work supported by the National Science Foundation under grant numbers: 1246120, 1525057, and 1413739 – [1], frame at 4:53 (CC BY 3.0) via Commons Wikimedia
2. “Maghemite silica nanoparticle cluster” By Marko Petek – Own work (CC BY-SA 4.0) via Commons Wikimedia