CERAMIC CAPACITORS

133

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General characteristics

Page revised 06/20

Substances which display only, or mostly, diamagnetic behavior are termed diamag-

netic materials, or diamagnets. Materials referred to as diamagnetic are those which

are usually considered by non-physicists as “non magnetic”, and include water, DNA,

most organic compounds such as petroleum and certain plastics, and many metals

such as mercury, gold and bismuth.

I.4. Ferromagnetism

Ferromagnetism is defined as the phenomenon by which materials, such as iron, in

an external magnetic field, become magnetized and remain so for a period after the

material is no longer in the field.

I.5. Magnetic Susceptibility

Magnetic susceptibility (Xv) is the degree of magnetization of a material in response

to an applied magnetic field. If Xv is positive, then (1+Xv) > 1 and the material is said

to be paramagnetic. In this case, the magnetic field is strengthened by the presence of

the material. Conversely, if Xv is negative, then (1+Xv) < 1, and the material is termed

diamagnetic. As a result, the magnetic field is weakened in the presence of the material.

Class

Xv dependant

on B?

Dependent on

temperature? Hysterisis?

Example

Xv

Diamagnetic

No

No

No

Water

–9 x 10–6

Paramagnetic

No

Yes

No

Aluminum

2.2 x 10–5

Ferromagnetic

Yes

Yes

Yes

Iron

3000

I.6. Units

The International System of Units (abbreviated “SI” from the French “Système Interna-

tional d’unités”) is the modern form of the metric system. It is the world’s most widely

used system of units, both in everyday commerce and in science. The older metric sys-

tem included several base units. The SI was developed in 1960 from the old meter-ki-

logram-second (MKS) system, rather than the centimeter-gram-second (CGS) system,

which, likewise, had a number of variants.

The SI introduced several newly named units. The SI is not static, but a living set of

standards in which units are created and definitions are modified through international

agreement as the technology of measurement progresses.

Parameter

CGS System

Correcting Factor

SI unit

Magnetic Induction B

G (gauss)

10–4

T (tesla)

Applied Field H

Oe (oersted)

103/4π

A/m

Magnetization Mg

emu/erg/G

1

A.m2/kg

Mass Susceptibility Xg

cm3/g

4π x 10–3

m3/kg

Permeability µ

–

4π x 10–7

H/m

NB: when a material is paramagnetic, the best way to describe it is in terms of magnetic

susceptibility Xg. When the material is ferromagnetic, magnetization Mg is preferred.

The following formula could be used:

Mg = Xg x H

One should also note that:

Xv = Xg. [density]

II. EXPERIMENTAL SETUP

II.1. Magnetometer

Measurements were taken using a Quantum Design magnetometer, model MPMS-5.

The MPMS provides solutions for a unique class of sensitive magnetic measurements

in key areas such as high-temperature superconductivity, biochemistry and magnetic

recording media. This began developing significantly in 1988 with the discovery of a

new class of superconducting materials. While the basic application has not changed

greatly, its use has expanded to more than 530 installations worldwide.

The modular MPMS design integrates a SQUID detection system - Superconducting

Quantum Interference Device, a precision temperature control unit residing in the bore

of a high field superconducting magnet, and a sophisticated computer operating sys-

tem:

Maximum Sample Size: 9 mm;

Field Uniformity: 0.01% over 4 cm;

Temperature Range: 1.9-400 K;

Sensitivity of 10–7 emu-CGS.

II.2. Superconducting Quantum Interference Device

The main components of a SQUID (see Fig. 1) magnetometer are: (a) a superconducting

magnet; (b) a superconducting detection coil which is coupled inductively to the sam-

ple; (c) a SQUID connected to the detection coil; (d) a superconducting magnetic shield.

A description of each one is given below:

Fig. 1

II.2.1. Superconducting Magnet

A superconducting magnet is a solenoid made of superconducting wires (see Fig. 2).

The solenoid must be kept at liquid helium temperature in a liquid-helium medium. The

uniform magnetic field is produced along the axial cylindrical bore of the coil. Supercon-

ducting solenoids that produce magnetic fields in the range 5-18 Tesla are now com-

mercially available. A superconducting magnet requires an appropriate programmable

bipolar power supply for operation.

Fig. 2

General Information