Described is pentamycin in a purity exceeding 95%, certain polymorphs and solvates of pentamycin, processes for their manufacture, and a method for decreasing the rate of degradation of pentamycin. Since this insulation layer has magnetic properties an increased amount of flux is transferred between the flux guide to the tunnel valve sensor for rotating a magnetic moment of a free layer in the tunnel valve sensor. In many instances the copolyesters, assuming they are not randomized in later transesterification reactions, have unique microstructures related to the sequencing of repeat units the their polymer chains. The first magnetic body and the second magnetic body are maintained in non-contact with each other.