Anomalous magnetic field dependence of T-AF in La0.95Sr0.05MnO3

The magneto-elastic properties of single-crystalline La0.95Sr0.05MnO3 have been studied ultrasonically. Our investigations focussed on the temperature interval where magnetic ordering starts to evolve and results in a spin ca nted antiferromagnetic ground state. In detail the experiments revealed tha t the magnetic order parameter in low-doped manganite is only weakly couple d to lattice strains. Furthermore, the anomalous temperature dependence of the order parameter as found resembles highly that in stoichiometric LaMnO3 . However, the main and most surprising finding is that external magnetic f ields favor the spin canted phase in La0.95Sr0.05MnO3. It is unclear at pre sent how the exchange interaction can be tuned by magnetic fields in the wa y observed and we are not aware of existing theoretical concepts which migh t give a plausible explanation for the unexpected field dependent behavior of the critical temperature. We believe, however, that this behavior primar ily results from the fact that the exchange interaction depends sensitively on the orbital configuration of the manganese d electrons.