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Colors and Magnetism

Colors and Magnetism

Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.

Diamagnetism

Diamagnetism

Materials consisting of paired electrons have zero net magnetic moments. However, when these materials are placed under an external magnetic field, the moments opposite to the field are induced. Such materials are called diamagnets. Diamagnetism is the response of the diamagnets when placed in an external magnetic field.
Diamagnetism was discovered by Anton Brugmans in 1778 when he observed that bismuth gets repelled by magnetic fields, thus theorizing that diamagnets get repelled by magnets.

Potential Due to a Magnetized Object

Potential Due to a Magnetized Object

Magnetic dipoles in magnetic materials are aligned when placed under an external magnetic field. For paramagnets and ferromagnets, dipole alignment occurs in the direction of the magnetic field. However, the dipoles align opposite to the field in the case of diamagnets. This state of magnetic polarization due to the external field is called magnetization. Magnetization is defined as the dipole moment per unit volume. It plays a similar role to polarization in electrostatics.
The vector...

Atomic Nuclei: Nuclear Relaxation Processes

Atomic Nuclei: Nuclear Relaxation Processes

In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis. This...

Paramagnetism

Paramagnetism

Paramagnets are materials with unpaired electrons that possess a finite magnetic moment. In the absence of a magnetic field, these moments are randomly oriented, and thus the net moment is zero. Under an external field, a torque acting on the moments tends to align them along the field's direction. However, the random thermal motion of electrons produces a torque opposite to the external field and tries to disorient the moments. These two competing effects align only a few moments along the...

Ferromagnetism

Ferromagnetism

Materials like iron, nickel, and cobalt consist of magnetic domains, within which the magnetic dipoles are arranged parallel to each other. The magnetic dipoles are rigidly aligned in the same direction within a domain by quantum mechanical coupling among the atoms. This coupling is so strong that even thermal agitation at room temperature cannot break it. The result is that each domain has a net dipole moment. However, some materials have weaker coupling, and are ferromagnetic at lower...

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Related Experiment Video

Updated: Jun 20, 2026

Resonance Fluorescence of an InGaAs Quantum Dot in a Planar Cavity Using Orthogonal Excitation and Detection

Resonance Fluorescence of an InGaAs Quantum Dot in a Planar Cavity Using Orthogonal Excitation and Detection

Published on: October 13, 2017

Light-induced spontaneous magnetization in doped colloidal quantum dots.

Rémi Beaulac¹, Lars Schneider, Paul I Archer

¹Department of Chemistry, University of Washington, Seattle, WA 98195-1700, USA.

Science (New York, N.Y.)

|August 22, 2009

Summary

Light induces spin polarization in manganese-doped quantum dots, creating internal magnetic fields. This enables spontaneous magnetic saturation up to room temperature without external fields.

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Last Updated: Jun 20, 2026

Resonance Fluorescence of an InGaAs Quantum Dot in a Planar Cavity Using Orthogonal Excitation and Detection

Resonance Fluorescence of an InGaAs Quantum Dot in a Planar Cavity Using Orthogonal Excitation and Detection

Published on: October 13, 2017

Correlative Light- and Electron Microscopy Using Quantum Dot Nanoparticles

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Published on: August 7, 2016

Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping

Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping

Published on: June 3, 2015

Area of Science:

Spintronics and Nanotechnology
Materials Science
Quantum Dot Research

Background:

Controlling spin effects in semiconductor nanostructures is crucial for advanced electronics.
Light is a promising tool for generating, manipulating, and reading out electron spins.

Purpose of the Study:

To demonstrate spontaneous photoinduced polarization of manganese(II) spins in colloidal cadmium selenide quantum dots.
To investigate the generation of internal exchange fields and their effect on spin polarization.

Main Methods:

Utilizing photoexcitation of manganese-doped cadmium selenide quantum dots.
Investigating the resulting dopant-carrier exchange fields and their impact on the semiconductor band structure.
Measuring magnetic properties at varying temperatures in the absence of external magnetic fields.

Main Results:

Photoexcitation generated significant dopant-carrier exchange fields due to spatial confinement.
Giant Zeeman splittings of the semiconductor band structure were observed without applied magnetic fields.
Spontaneous magnetic saturation of manganese(II) spins was achieved at zero external magnetic field up to approximately 50 Kelvin.
Photomagnetic effects persisted up to room temperature.

Conclusions:

Spontaneous photoinduced spin polarization in doped quantum dots offers a novel pathway for spintronic applications.
The observed giant Zeeman splittings and room-temperature photomagnetism highlight the potential of these materials.
This work paves the way for developing magnetic semiconductor nanostructures controlled by light.