Study of covalent spin interactions in Cd1-xMnxSe by cryobaric magnetophotoluminescence

Pressure dependence of exchange interactions among small Mn clusters scattered throughout the network of sp3 covalent bonds in a diluted magnetic semiconductor Cd1-xMnxSe has been studied by a cryobaric measurement of the exciton magnetophotoluminescence. The pressure is generated up to 2 GPa with a diamond anvil cell, being subjected at low temperatures to the static magnetic field up to 23 T generated with a hybrid magnet. The observed specific spin temperature T0 of the clusters gives the effective internal exchange constant J*/k≡J2/k +(10/3)J3/k +2J4/k to be –2.0±0.4 K at 1 atm, where Jn denotes nth-neighbor exchange constant. The nearest-neighbor interaction constant is obtained to be J1/k = -7.4±0.4 K at 1 atm from an analysis of the effect of the stepwise magnetization of Mn pairs. J*, as well as J1, increases rapidly with increasing pressure. The pressure coefficient dln|J*|/dP = 0.2-0.4 GPa-1 agrees with dln|J1|/dP = 0.25±0.05 GPa-1 within experimental errors. This result supports Larson's covalent spin interaction picture that the exchange interactions between the scattered, localized spins are determined by kinetic exchanges mediated by the extended p orbitals making the valence band of the host II-VI semiconductor.