# A Study of Reversible and Irreversible Magnetization Behaviour in Conventional Superconductors

## Abstract

^{1}that there exists a thermodynamic reversible region in (

*H,T*) space just below the normal-superconductor phase boundary (

*T*

_{ c }(

*H*) line). Here

*H*is the applied field,

*T*is the temperature of the sample. Hysteretic behaviour sets in only below the irreversibility line, (

*T*

_{ r },

*H*

_{ r }), and different techniques have been used to determine this (

*T*

_{r},H

_{r}) line in the HTSC. We have searched for such an irreversibility line in specimens of conventional type I and type II superconductors by both dc and ac magnetization techniques. The following four different procedures were employed to determine the (

*H*

_{ r },

*T*

_{ r }) line in HTSC:

- (a)
Field-cooled (FC) and zero field-cooled (ZFC) magnetization curves in a constant dc field

*H*were measured as a function of temperature. The temperature at which these merge [*T*_{ r }(*H*)] gives a point on the irreversibility line. - (b)
Hysteretic isothermal magnetizaton, i.e,

*M vs H*, curves were measured where*M*is the sample’s magnetization per unit volume and*H*is the applied field. The field, [*H*_{ r }(*T*)], at which the hysteresis vanishes gives a point on the (*T*_{ r },*H*_{ r }) line. - (c)
The complex ac magnetic susceptibility (χ = χ′

_{ H }+*i*χ″_{ H }) was measured in constant dc field*H*as a function of temperature. A thermoaynamic response requires that χ′_{ H }(T) be positive just below*T*_{ c }and this is called the*Differential Paramagnetic Effect*(DPE).^{2}The temperature at which χ′_{ H }(T) switches from positive to negative is identified with*T*_{ r }(*H*). - (d)
From the simultaneous measurements of χ″

_{ H }(T) as a function of temperature in a constant dc field, the temperature at which it peaks is identified as*T*_{ p }(*H*).

## Keywords

Hysteresis Loss Perpendicular Orientation Disc Plane Irreversibility Line Conventional Superconductor## Preview

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