PHASE TRANSITIONS IN ANTIFERROMAGNETS IN EXTERNAL MAGNETIC FIELDS: MOSSBAUER SPECTRO SCOpy

Known antiferronlagnetic nlaterials far out nwnber known ferronlagnetic and ferrinlagnetic nlaterials. More­ over, the antife rronlagnets display a wide variety of phase transitions in addition to the paranlagnetic to antiferro­ nlagnetic transition at the Neel point, that nlake thenl a rich source of infornlation about the relations hip between exchange interactions, structure, and phase transition phenonlena. Mossbauer spectroscopy has been used ex­ tensively over the last decade to study antiferrornagnets, capitalizing on the fact that the nlagneti c hyperfine field is proportional to the sublattice nlagnetization. In general, these studies have concentrated on deternlining the nlagnetic structure below TN and the sublattice nlagnetization as a function of T below TN' in SOnle cases in the critical region. Less well stuCiied are those transitions in anti­ ferronlagnets which are induced by external nlagnetic fields, although in these cases too, Mo'ssbauer spectro­ scopy can provide inlportant and often unique infornlation.