John Blackburn

A new magnetic recording read head technology based on the magneto-electric effect

The existing magnetic recording read head technologies use one of the well-known magneto-resistance effects (i.e. anisotropic magneto-resistance, giant magneto-resistance or tunnelling magneto-resistance (TMR)) to read back the data from the magnetic recording medium. These are usually sophisticated devices that require a dc test current flowing through the sensor stack in order to measure its change in resistance (i.e. amplitude response signal) as a function of the fringing magnetic flux of the recorded bits, when the reader moves along the recorded track. In this paper, we propose the design of a new kind of highly sensitive read sensor for magnetic recording heads, which directly produces a voltage response without the need for a test current. This new design is based on the magneto-electric effect in laminated multiferroic materials. Such a magnetic read head is much simplified in terms of sensor construction (i.e. number of layers involved and horizontal biasing requirements) and has a range of potential advantages including similar sensitivity to that of the TMR heads, reduced power consumption, better thermal performances, excellent high frequency operation and reduced cost of production.

Nonlinear piezoelectric resonance: A theoretically rigorous approach to constant I−V measurements

Methods for piezoelectric characterization include the standard resonance test. At higher powers, however, the material’s inherent nonlinearity acts to significantly affect the expected resonance response. High-power resonance methods have previously been developed to describe piezoelectric nonlinearity. In this article we specify and describe the approximations adopted in the current theory and propose a more rigorous theory derived from fundamental principles. We first use thermodynamics to derive the form of the constitutive equations. In particular, we propose that the envelope rather than instantaneous values of stress, strain, and electric field must appear in these equations to yield a type of nonlinearity which, nonetheless, yields a sinusoidal current for sinusoid applied voltage. An alternative approach is set out describing the highly nonlinear experimental data by fitting just one adjustable material parameter to the entire impedance response measured around resonance. Theoretical descriptions...

Multiferroic magnetic recording read head technology for 1 Tbit/in.2 and beyond

Multiferroic (MF) materials are very promising candidates for new technologies and applications because they exhibit simultaneously multiple cooperative phenomena (i.e., magnetic, electric, and piezoeffects). The main feature of MF materials is the magnetoelectric (ME) effect, which can be used to engineer highly sensitive magnetic/electric sensors. In this paper, we discuss the requirements of a new kind of magnetic recording read head for 1Tbit∕in.2 recording densities, which is based on a MF structure. The MF sensor operates at room temperature via the strain mediated ME effect by producing a voltage signal in response to the magnetic field excitation from the recorded bits. We calculated the theoretical output from such a recording read head assuming a magnetic recording density of 1Tbit∕in.2. Our calculations demonstrate that the proposed read head technology could replace in the future the conventional magnetoresistive read heads bringing also a number of considerable advantages, as detailed in the ...

Verified finite element simulation of multiferroic structures: Solutions for conducting and insulating systems

Composite multiferroics are an exciting class of engineered materials with a wide range of existing and potential applications. This paper describes an original finite element (FE) simulation for composite multiferroic devices. Detailed analysis is given on the flow of electric/magnetic fields between the composite regions with attention given to the conductivity of the magnetostrictive layers (piezoelectric assumed to be insulating). The simulation is verified against an existing FE code and against a theoretical analysis, also presented here. The issue of boundary and continuity conditions is discussed in detail and approximations made in both FE and analytical treatments are specified. We derive the I-V curves of the composite device when acting as a magnetic field detector, in both conducting and insulating cases. The magnetic field detector acts as a voltage source: we calculate its open-circuit voltage and internal impedance in each case.

Non-linear piezoelectric resonance analysis using burst mode: a rigorous solution

The burst mode experiment is commonly used to measure non-linear piezoelectric material properties. However, the theory that is often employed is highly simplified, making use of linear results. Here we represent a more rigorous theory based closely on the underlying non-linear partial differential equations. Since time domain solutions are not available analytically, the approach is in two parts: the PDE is solved in the frequency domain, then an auxilliary non-linear ordinary differential equation is solved in the time domain. Comparison of the two yields the material parameters. Also, we suggest the excitation portion of the I(t) curve be studied rather than the decay part normally used since the former contains more features, has a well-defined initial condition (current and charge both zero) and is less susceptible to experimental artefacts.

Correlation of electron backscatter diffraction and piezoresponse force microscopy for the nanoscale characterization of ferroelectric domains in polycrystalline lead zirconate titanate

The functional properties of ferroelectric ceramic bulk or thin film materials are strongly influenced by their nanostructure, crystallographic orientation, and structural geometry. In this paper, we show how, by combining textural analysis, through electron backscattered diffraction, with piezoresponse force microscopy, quantitative measurements of the piezoelectric properties can be made at a scale of 25 nm, smaller than the domain size. The combined technique is used to obtain data on the domain-resolved effective single crystal piezoelectric response of individual crystallites in Pb(Zr0.4Ti0.6)O3 ceramics. The results offer insight into the science of domain engineering and provide a tool for the future development of new nanostructured ferroelectric materials for memory, nanoactuators, and sensors based on magnetoelectric multiferroics.

Emerging technologies and opportunities based on the magneto-electric effect in multiferroic composites

Multiferroic materials are recognized today as one of the new emerging technologies with huge potential for both academic research and commercial developments. Multiferroic composites are in particular more attractive for studies due to their enhanced properties, especially at room temperature, in comparison to the single-phase multiferroics. In this paper, we examine some of the theoretical aspects regarding one type of multiferroic composites (laminated structures) and we discuss one of the many possible applications of these exciting structures. We highlight the main advantages composite systems have over single-phase multiferroics and the similarities that exist between them.

Composite multiferroics as magnetic field detectors: how to optimise magneto-electric coupling

Abstract Abstract We present a computer simulation and theoretical study of composite multiferroics acting as magnetic field detectors. Our set-up consists of a layer of piezoelectric sandwiched between two magnetostrictive layers. When magnetic field is applied the magnetostrictive strains and this is passed onto the piezoelectric producing a detectable voltage. We model the device using our own finite element code and calculate open circuit voltage and input impedance. Good agreement is shown with analytical formulas. We then optimise the coupling by altering the ratio of piezoelectric to magnetostrictive volume and the shape of the inner piezoelectric layer: the former effect is more important. We show that nearly equal amounts of piezoelectric and magnetostrictive give best coupling but the exact optimal ratio depends on the relative stiffnesses of the two materials. Most calculations carried out in previous literature have assumed that the magnetic field found in the device is simply the applied field. Here we show to what extent such an applied field can enter the device by simulating also the air region around the detector. The field in the device is calculated to be ∼17% less than the applied field.

Compressive Current Response Mapping of Photovoltaic Devices Using MEMS Mirror Arrays

Understanding the performance and aging mechanisms in photovoltaic devices requires a spatial assessment of the device properties. The current dominant technique, electroluminescence, has the disadvantage that it assesses radiative recombination only. A complementary method, laser beam-induced current (LBIC), is too slow for high-throughput measurements. This paper presents the description, design, and proof of concept of a new measurement method to significantly accelerate LBIC measurements. The method allows mapping of the current response map of solar cells and modules at drastically reduced acquisition times. This acceleration is achieved by projecting a number of mathematically derived patterns on the sample by using a digital micromirror device (DMD). The spatially resolved signal is then recovered using compressed sensing techniques. The system has fewer moving parts and is demonstrated to require fewer overall measurements. Compared with conventional LBIC imaging using galvanic mirror arrangements or xy scanners, the use of a DMD allows a significantly faster and more repeatable illumination of the device under test. In this proof-of-concept instrument, sampling patterns are drawn from Walsh-Hadamard matrices, which are one of the many operators that can be used to realize this technique. This has the advantage of the signal-to-noise ratio of the measurement being significantly increased and thus allows elimination of the standard lock-in techniques for signal detection, reducing measurement costs, and increasing measurement speed further. This new method has the potential to substantially decrease the time taken for measurement, which demonstrates a dramatic improvement in the utility of LBIC instrumentation.

Small-scale piezoelectric devices: Pyroelectric contributions to the piezoelectric response

The recent trend in miniaturization of piezoelectrically active devices is driving research on size effects of these functional materials under reduced length scales. In this paper, we measure and model the generation of charge in thin piezoelectric structures under sinusoidal hydrostatic pressure and show how the subsequent thermally induced pyroelectric effect dominates the response in the smallest samples. We calculate the temperature profiles through the lead zirconate titanate structures, and determine the pyroelectric coefficient in these materials to be p′=0.28±0.02 mC m−2 K−1. The analysis of the piezoelectric and pyroelectric charge response described in this paper has significant impact on the design and fundamental functional behavior of small-scale piezoelectric devices.