The study of changes in the refractive indices (with consequent changes of birefringence) of a transparent magnetic crystal which accompany changes in the magnetic order is becoming more popular. The authors review why this is. The first reason is that birefringence can be measured very accurately: the different experimental arrangements are reviewed. The second reason is because a birefringence measurement is an integrational spectroscopic technique and therefore it is studied both experimentally and theoretically as a branch of magneto-optics and hence gives information on the detailed energy level structure of the solid. The third reason is that in a number of interesting systems the birefringence is proportional to the magnetic energy over a wide temperature range and it is often a more convenient method of obtaining the magnetic specific heat than direct specific heat measurements; this is particularly true in magnetic crystals which show low dimensional ordering. The last reason is that in all magnetic crystals the birefringence change should vary like one of the thermodynamic critical exponents near to the phase transition. They review in detail the reasons why birefringence studies have become so successful for measuring critical exponents in pure and particularly mixed crystals.

https://iopscience.iop.org/article/10.1088/0034-4885/47/5/002/pdf

Linear optical birefringence of magnetic crystals

Phenomenological analysis of the linear magnetic birefringence in dysprosium iron garnet

Anomalous magnetic reordering in magnetodielectric terbium iron garnet at low temperatures

Accurate measurement of the γe, 2 magnetostriction constant of a single crystal of TbIG has been performed from 90 K up to the Neel temperature. Both spontaneous and forced magnetostriction differ markedly from the one ion model predictions. Moreover, the forced magnetostriction modulus is much stronger below the compensation temperature than expected from extrapolating the high temperature variations. The spontaneous [111] linear magnetic birefringence and its field derivative exhibit thermal variations proportional respectively to those of the spontaneous and forced magnetostriction from 80 to 200 K.

A refined study of the [111] magnetoelastic properties of terbium iron garnet: Relation to the cotton mouton birefringence

Crystal field effects in terbium iron garnet

The specific circular φF and linear φCM magnetic birefringences of Tb3 Fe5 O12 single‐crystal are reported as a function of the d.c. field Ha and from liquid helium temperature to room temperature. The sign, amplitude and slope of the Cotton‐Mouton effect are strongly dependent on T, Ha and on the direction of this field with respect to the crystal axis. Well defined maxima of % % the slope ΔφF/ΔHa and ΔφCM/ΔHa, observed near T=45 °K, are discussed both from the paramagnetic evolution of the Tb3+ ions in the anisotropic exchange and crystal fields which induce a noncolinear magnetic structure.

A. Lepaillier‐Malécot

Papers

Magnetooptical and magnetic properties of terbium iron garnet at low temperatures