Diamagnetic substances

A Gouy balance is used to observe the magnetic character of a sample by detecting the extent to which it is drawn into (paramagnetic substances) or driven out of (diamagnetic substances) a magnetic field. 

Diamagnetism Substances that have no unpaired electrons are diamagnetic. When placed in an applied magnetic field, their induced magnetic fields oppose the applied magnetic field. 

A diradical is likely to be more polarizable and a stronger base than the corresponding singlet state. If so, reaction with an acid should shift the equilibrium enough for the diradical to be detectable in otherwise diamagnetic substances. This seems to be the case for the substances shown below, in which paramagnetic resonance absorption indicates the presence of the diradical conjugate acid to the extent... 

This article concerns a simple expedient whereby short-lived reactive free radicals may be transformed into more persistent paramagnetic species, thus enabling esr techniques to be applied to systems in which the concentration of the reactive radical remains below normal detection limits. The principle is a simple one. It depends upon the addition to the reaction system of a small quantity of a diamagnetic substance (the spin-trap ) having a particularly high affinity for reactive radicals the product of this trapping reaction must be a particularly persistant free radical (the spin adduct ) whose concentration will build to readily detectable levels (>ca. 10—7—10-6 M). The general reaction is represented by equation (1). 

Diamagnetism is a basic property of all substances and involves a slight repulsion by a magnetic field. The magnetic susceptibility of a diamagnetic substance is small (-10 ), negative and independent of temperature. Iron oxides display additional types of magnetism. 

The relations between paramagnetic and ferromagnetic properties and structure are less simple than in the case of diamagnetic substances, and will not be dealt with here the reader is referred to the review by Lonsdale (1937 a). 

Diamagnetism.—It was discovered by Faraday that most substances when placed in a magnetic field develop a magnetic moment opposed to the field. Such a substance is said to be diamagnetic. (Substances that develop a moment parallel to the field are called paramagnetic substances.)1... 

A sample of a diamagnetic substance placed in an inhomogeneous magnetic field is acted on by a force that tends to push it away from the strongfield region. This force is proportional to the diamagnetic susceptibility of the substance, which is defined as the ratio of the induced moment, /x, to the field strength, H ... 

There is a common misapprehension that a bar of a paramagnetic substance in a uniform magnetic field sets itself parallel to the lines of force of the field and that a bar of diamagnetic substance sets itself perpendicular to the lines of force in fact, a bar of substance either paramagnetic or diamagnetic sets itself parallel to the lines of force in a uniform field. 

The value of k will be negative for a diamagnetic substance and positive for one that is paramagnetic. 

In diamagnetism substances are repelled by a magnetic field this property is associated with all closed electron shells. Paramagnetic substances are attached into a magnetic field, the force being related to the magnetic susceptibility. Paramagnetism normally arises from the spin of unpaired electrons. The Curie law for the susceptibility per mole (cm) is... 

Magnetic Properties Solids can be classified into different types depending upon their behaviour towards magnetic fields. The substances which are weakly repelled by magnetic field are called diamagnetic substances. For example, Ti02 andNaCl. Diamagnetic substances have all their electrons... 

For a paramagnetic substance, x is positive for a diamagnetic substance, it is negative. It is a dimensionless number, ordinarily very small in comparison with unity (except in the case of ferromagnetism) and essentially independent of H for fields readily available in the laboratory. 

Figure 8.2. Different types of magnetic behavior (a) a typicai M-H curve (both axes in Tesias) of a paramagnetic substance (b) a diamagnetic substance and (c) a ferromagnetic substance (note the change in the scaie of the M axis). An isotropic singie crystai, or poiycrystai with random crystaiiite orientation, is assumed.

The diamagnetic susceptibility is a measure of the averaged electronic distribution in bulk matter. Careri et al. (1977, 1980) showed that the differential diamagnetic susceptibility per gram of water adsorbed on lysozyme powders reached the bulk water value at 0.2 h. Lysozyme behaved as a normal diamagnetic substance. The diamagnetic susceptibility and the enthalpy of sorption for lysozyme change similarly at low hydration. 

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