MAGNETIC TRILAYERS WITH BILINEAR AND BIQUADRATIC EXCHANGE COUPLINGS -CRITERIA FOR THE MEASUREMENT OF J(1) AND J(2)

We have analytically calculated phase boundaries of magnetic trilayers with bilinear and biquadradic exchange couplings in order to investig ate possible phase transitions in these systems as the external magnet ic field, applied either along an easy or a hard magnetization axis, i s varied. A simple scheme is obtained for both antiferromagnetic and f erromagnetic couplings that is shown to be consistent with magnetizati on curves previously measured in different systems. In addition, exper imental data regarding static and dynamic responses in sputtered (100) Fe(40 Angstrom)/Cr(t(Cr))/Fe(40 Angstrom) are reported for the Cr thi ckness in the range 15 Angstrom < t(Cr) < 35 Angstrom. As a result, ou r model calculations indicate that the bilinear and biquadratic exchan ge coupling constants, J(1) and J(2), cannot be accurately determined from a fit to the experimental data when the ratio J(2)/\J(1)\ > 1, an d if only the main magnetization axes are considered. [S0163-1829(98)0 2725-8].