Complex nature of magnetic field induced ferroelectricity in GdCrTiO5
Résumé
This work shows an unconventional route for spin-driven ferroelectricity originating from a metastable magnetic field-induced canting of the chromium sublattice in the presence of gadolinium moments in GdCrTiO5 at low temperatures. Compared to the isostructural neodymium compound, significant differences of magnetism and magnetoelectric effects are seen. We present the results of thorough investigations of temperature and magnetic field dependent magnetization as well as ac and dc magnetic susceptibility. These bulk measurements are complemented by local-probe spectroscopy utilizing electron-spin resonance and muon-spin rotation/relaxation for probing the chromium moments. Ferroelectric order is inferred from pyro-and magnetocurrent measurements. GdCrTiO5 shows a pyrocurrent signal around 10 K, only if the system is cooled in an applied magnetic field exceeding 10 kOe. A distinct spin-driven ferroelectric order is revealed in this state for temperatures below 10 K, which can be switched by changing the magnetic-field direction and the polarity of the electric field. The magnetic measurements reveal no clear signature of long-range magnetic ordering. The presence of such "meta-magnetoelectric-type" behavior in the absence of any "meta-magnetic" behavior is rare in literature. Our microscopic spectroscopy results indicate significant changes of the magnetic properties around similar to 10 K. Probably there exists exchange frustration between Gd and Cr moments, which prevents long-range magnetic ordering at higher temperatures. Below 10 K, weak ferromagnetic magnetic order occurs by minimizing frustration due to lattice distortion, which supports magnetoelectric coupling. However, nonpolar distortions attain appreciable values after application of magnetic fields above 10 kOe, obviously breaking spatial inversion symmetry and creating ferroelectricity.