Magnetic Anomaly and Dielectric Tunability of (Sr,Mn)TiO₃ Thin Films

Abstract

Polycrystalline Sr_0.98Mn_0.02TiO₃ thin films are prepared by sol-gel spin-coating method on Si/SiO₂/TiO₂/Pt substrates. Their dielectric permittivity, polarization, and magnetization are investigated as a function of temperature (from 10 to 300 K), electric and magnetic fields. Temperature dependences of the magnetization M ^ZFC-FH(T), real part of the dielectric permittivity ϵ′(T), and dissipation factor tanδ(T) of Sr_0.98Mn_0.02TiO₃ films show anomalies around 41–45 K, implying an interrelation between polar and magnetic order. “Butterfly”-like dc bias dependences of the real part of the dielectric permittivity ϵ′(E _dc), as well as slim polarization and magnetization hysteresis loops are observed, suggesting that Sr_0.98Mn_0.02TiO₃ thin films belong to “multiglass” systems.

Keywords:

• Multiferroics
• thin films
• magnetisation
• dielectric polarisation; permittivity
• dielectric losses
• electric field effects
• sol-gel processing

Acknowledgments

Thanks are due to the FCT (Portuguese Foundation for Science and Technology) and DAAD/GRICES (Acções Integradas Luso-Alemãs) for financial support.

Special thanks to Prof. Wolfgang Kleemann. It is a great pleasure for us to join this special edition of Ferroelectrics in the honour of Professor Wolfgang Kleemann. And we are thankful to Dr. Jan Petzelt for having invited us to join this project. It is also a great pleasure to see that many of us share similar feelings: our admiration for Wolfgang Kleemann, a man that markedly contributed to the physics of functional materials. We have been collaborating with Prof. Kleemann since 2007, under Bilateral Actions between Portugal (FCT) and Germany (DAAD) and the European Project MULTICERAL. Our common interests in incipient ferroelectrics, such as strontium titanate, SrTiO₃, triggered our relation and led us to have important contributions in the field. Worth noting is the proposal of the coexistence of long-range electric and magnetic order in Sr_0.98Mn_0.02TiO₃ ceramics via a ‘‘multiglass’’ scenario of two different glassy states. Sr-site substituted Mn²⁺ ions are at the origin of both a polar and a spin glass with glass temperatures Tg 38 K and 34 K, respectively. The structural freezing triggers that of the spins, and both glassy systems show individual memory effects. Thanks to strong spin-phonon interaction within the incipient ferroelectric host crystal SrTiO₃, large higher order magnetoelectric coupling occurs between both glass systems. The paper that we present now reports new data obtained within this collaboration and reports the magnetic and dielectric behaviour of Mn doped SrTiO₃ thin films. It has been very rewarding and a pleasure working in close collaboration with someone like Wolfgang Kleemann.