SHAPE DEPENDENT FIELD INHOMOGENEITY OF HOMOGENEOUS SPECIMEN: CONSEQUENCES IN HR PMR IN SOLIDS

S.Aravamudhan

Department of Chemistry, North Eastern Hill University, PO NEHU Campus, Mawkynroh Umshing, East Khasi Hills District, Shillong, 793022, Meghalaya, INDIA

Magnetization within a material is inhomogeneous for specimen of shapes other than the regular ellipsoids. Whilediscussing the demagnetization effects in a (homogeneously) magnetized sample,it becomes necessary to describe the hypothetical Lorentz sphere (Inner Volume Element: I.V.E.) around a specific site. This has brought in a compulsion that for HR PMR in solids a spherical outer shape for the specimen must be ensured for the possibility that the induced field at a specific site due to bulk susceptibility is zero ¹.The material within the IVE is effectively absent (a cavity) if the contributions of the molecules within this IVE is calculated independently and taken into account finally. Similarly, if the outer macro shape and the inner [IVE] shape are both ellipsoids and with same ellipticity, then the induced field within the inner element can be zero as much as for the spherically shaped sample specimen. Moreover, it has been found that the contribution from the neighboring molecules within the ellipsoidal IVE can be the same as the spherical IVE². For shapes other than ellipsoids, since the magnetization would be inhomogeneous within the sample, calculating contributions at one representative point within the sample would not be enough. Thus, it would be necessary to calculate the induced fields at every one of the points of interest independent of the other points. Even for shapes other than ellipsoidal, if the shape is describable as regular, then an IVE can be carved out with the same shape, and, proportionate shape factors. However, defining a demagnetization factor in such cases, even when it becomes possible, is associated with limitations. Because a simple summation procedure for calculating demagnetization factors is now known³ it seems it would be possible to consider the case of such inhomogeneously magnetized specimen with much better ease and to use the results with better confidence⁴. If the requirement of single crystal spheres could become less stringent in HR PMR studies in solids then the technique can be applied with much less constraints.