Interface-driven magnetocapacitance in a broad range of materials

Triggered by the revival of multiferroic materials, a lot of effort is presently undergoing as to find a coupling between a capacitance and a magnetic field. We show in this report that interfaces are the right way of increasing such a coupling provided free charges are localized on these two‐ dimensional defects. Starting from commercial diodes at room temperature and going to grain boundaries in giant permittivity materials and to ferroelectric domain walls, a clear magnetocapacitance is reported which is all the time more than a few percent for a magnetic field of 90kOe. The only tuning parameter for such strong coupling to arise is the dielectric relaxation time which is reached on tuning the operating frequency and the temperature in many different materials. Following the “revival” of multiferroic materials [1], many research groups are looking for a coupling between a magnetic field and the dielectric permittivity of materials. Not only applications but also the basic understanding is the driving force for such an extended effort. Since the number of materials which display simultaneously ferroelectric polarization and magnetic order at room temperature is rather limited [2,3], one is looking for alternative routes. More specifically, concerning the magnetocapacitance, a direct room temperature coupling of an external magnetic field with microscopic polarisabilities is still to be found. This is why integrated [4] and bulk [5] composites have been designed as to increase the density of interfaces between ferroelectric and ferromagnetic materials. In piezoelectric‐based devices, the generation of a ac current at the piezo resonance is readily achieved [6]. Very recently this effect driven by elastic deformation has been found in very standard Multi Layer Ceramic Capacitors [7] which opens a broad range of applications. Nonetheless room temperature magnetocapacitance, i.e. the change of a capacitance by a magnetic field is still an open question. Recently, Catalan has shown that non‐linear resistance at interfaces can be the right way to find such an effective coupling [8]. In this report, we apply this concept to several and very different materials. In a first step, we recall that non‐linear resistance of diodes is of everyday use to sense magnetic field. In the blocking regime, it is thus very easy to observe room temperature 15% magnetocapacitance in 1cent diodes provided the operating frequency is set in the right range. We will then move to so‐called “giant permittivity” materials [9‐12] which include charged interfaces [13‐15]. Setting the temperature, in the right range a magnetocapacitance is observed in the case of CaCu3Ti4O12, an archetype of giant permittivity materials. At last, we focus on more mesoscopic interfaces which are charged ferroelectric domains walls in Fe doped BaTiO3. A magnetocapacitance is clearly seen in the temperature and frequency range where the domain walls are relaxing. With this collection of results in many different materials we demonstrate that effective magnetocapacitance is a very general trend of charged interfaces materials.