SUPERPARAMAGNETISMSUPERPARAMAGNETISMLimits and ApplicationsLimits and Applications

Langevin function (red line), compared with tanh(x / 3) (blue line).

Superparamagnetism occurs in nanoparticles which are Superparamagnetism occurs in nanoparticles which are single-domain, i.e. composed of a single magnetic domain. single-domain, i.e. composed of a single magnetic domain.

This is possible when their diameter is below 3-50 nm, This is possible when their diameter is below 3-50 nm, depending on the materials. depending on the materials.

In this condition, it is considered that the magnetization of In this condition, it is considered that the magnetization of the nanoparticles is a single giant magnetic moment, sum the nanoparticles is a single giant magnetic moment, sum of all the individual magnetic moments carried by the of all the individual magnetic moments carried by the atoms of the nanoparticle. atoms of the nanoparticle.

Metal nanoclusters of an element behave differently Metal nanoclusters of an element behave differently than bulk matter of the same element.than bulk matter of the same element.

d-orbital overlap reduces magnetic moment per d-orbital overlap reduces magnetic moment per atom.atom.

Metal nanoclusters exhibit magnetic shell Metal nanoclusters exhibit magnetic shell phenomenonphenomenon

Metal nanoclusters do not lose their magnetization Metal nanoclusters do not lose their magnetization as quickly above the Curie temp.as quickly above the Curie temp.

Metal nanoclusters exhibit superparamagnetic Metal nanoclusters exhibit superparamagnetic behavior.behavior.

Superparamagnetism provides a theoretical Superparamagnetism provides a theoretical minimum size per bit in magnetic moment based minimum size per bit in magnetic moment based memory systemsmemory systems

BASIS FERROMAGNETISMBASIS FERROMAGNETISM

Materials: Fe, Co, Ni, GdMaterials: Fe, Co, Ni, Gd

Spins of unfilled d-bands spontaneously Spins of unfilled d-bands spontaneously align parallel inside a align parallel inside a domain domain below a below a critical temperature Tcritical temperature TCC (Curie) (Curie)

Ferro-magnetism:Ferro-magnetism:

HYSTERESIS LOOP OF FERROMAGNETIC MATERIALSHYSTERESIS LOOP OF FERROMAGNETIC MATERIALS

SUPERPARAMAGNETISM - A SIZE EFFECTSUPERPARAMAGNETISM - A SIZE EFFECT

Magnetic Properties of Nanostructured Materials:Magnetic Properties of Nanostructured Materials:

SUPERPARAMAGNETISM - A SIZE EFFECTSUPERPARAMAGNETISM - A SIZE EFFECT

SuperparamagnetismSuperparamagnetism

EVOLUTION OF MAGNETIC DATA STORRAGEEVOLUTION OF MAGNETIC DATA STORRAGE

LIMITS AND APPLICATIONSLIMITS AND APPLICATIONS

Magnetic Data StorageMagnetic Data Storage:

Solutions to minimize bit size:Solutions to minimize bit size:

APPLICATIONS OF SUPERPARAMAGNETISMAPPLICATIONS OF SUPERPARAMAGNETISM

Biomedical applicationsBiomedical applications

• • DetectionDetection: MRI Magnetic Resonance Imaging: MRI Magnetic Resonance Imaging

• • SeparationSeparation: Cell-, DNA-, protein- separation, RNA fishing: Cell-, DNA-, protein- separation, RNA fishing

• • TreatmentTreatment: Drug delivery, hyperthermia, magnetofaction: Drug delivery, hyperthermia, magnetofaction

Other applications:Other applications:

• • Ferrofluid: Ferrofluid: Tunable viscosityTunable viscosity

• • SensorsSensors: high sensitivity (GMR, BARCIII): high sensitivity (GMR, BARCIII)

• • SelfSelf - Assembling - Assembling

SPIONSPION = = SS uperparamagnetic uperparamagnetic I I on on OO xide xide NN anoparticle anoparticle

Particles with attached drug can be injected and guided Particles with attached drug can be injected and guided through the body by application of an external field.through the body by application of an external field.

??? WHY SUPERPARAMAGNETIC PARTICLES ?????? WHY SUPERPARAMAGNETIC PARTICLES ???

Therapeutic effect on several types of tumoursTherapeutic effect on several types of tumours• • Injection of superparamagnetic nanoparticlesInjection of superparamagnetic nanoparticles• • translocation of the particles to the tumourtranslocation of the particles to the tumour• • uptake of the nanoparticles by cancerous cellsuptake of the nanoparticles by cancerous cells• • application of an external alternative magnet application of an external alternative magnet fieldfield––> provides energy for the magnetic moments to > provides energy for the magnetic moments to change magnetisation directionchange magnetisation direction

––> Superparamagnetic relaxation: dissipated > Superparamagnetic relaxation: dissipated energy = energy = heatheat

• • Cancerous cells have higher temperature Cancerous cells have higher temperature senstivity than healthy cellssenstivity than healthy cells

• • No danger of thrombosis, no remanent No danger of thrombosis, no remanent magnetisation!magnetisation!