The two main difficulties encountered in the design of a sensitive hysteresis loop tracer for thin magnetic films are the flux calibration and the reduction of noise. The aim of this paper is to examine their nature and to show the possible solution for the design of very sensitive hysteresis loop tracers. The study of the flux distribution around a thin magnetic film specimen permits determination of the merits of various pickup coil configurations, as well as the form which optimizes the signal‐to‐noise ratio. The various disturbing voltages and the ways to eliminate them are examined. Optimization of the amplifier noise figure, proper choice of the integration network, dc restoration, and hum synchronization are described for the reduction of the output noise after integration and amplification. Two instruments built according to these principles are outlined. The first has a single wire pickup and is well suited for measurement of the flux distribution around a thin magnetic film and for experiments in vacuum at elevated temperatures; the second is more flexible and sensitive. By using different pickup coils covering a frequency range from 50 cps to 10 kc, its sensitivity is sufficient to measure flux values of 2×10−12 v‐sec at a frequency of 500 cps.

Sensitive Flux Measurement of Thin Magnetic Films

An instrument for measurement of the low frequency magnetic properties of thin layers is described. The difference signal from two opposed pick‐up coils, one of which contains the sample, is amplified, integrated, and amplified again to cause the vertical deflection of a cathode‐ray oscillograph to be proportional to the intensity of magnetization of the specimen. A signal is applied to the horizontal deflecting plates of the oscillograph to cause it to represent the applied magnetizing field in the region of the pick‐up coils. A large reduction in low frequency noise in the difference signal preamplifier is accomplished by use of a circuit similar to electrometer tube circuits. Noise introduced through integration of sharp peaked signals is reduced by use of first and third harmonic components in the magnetizing field current. A signal equal to noise is produced by a flux change of 75×10−6 maxwell.

Magnetization Hysteresis Loop Tracer for Long Specimens of Extremely Small Cross Section

A simple form of 60‐cps hysteresis loop tracer for materials of high and low permeability is described. By including a differential form of balance control, all 60‐cps voltage present in the leads and pickup coils, prior to the insertion of a magnetic specimen into the field coils, may be completely balanced out. The sensitivity is sufficient to provide a one‐inch peak to peak deflection on a Dumont 304A cathode‐ray oscilloscope for a flux change of 0.1 maxwell.

Simple 60‐cps Hysteresis Loop Tracer for Magnetic Materials of High or Low Permeability

This chapter provides an overview of the various techniques for the growth and characterization of magnetic thin films and nanostructures. The chapter is divided broadly into two parts: the first part focuses on growth and characterization for magnetic thin films and multilayer in general. In the second part, emphasis is on the use of advanced techniques for the fabrication and characterization of magnetic nanostructures. Various examples of lithographic and other controlled nanofabrication techniques are discussed. Practical examples on how the static and dynamic properties of magnetic nanostructures are characterized using a combination of magneto-optical Kerr effect measurements, magnetic force microscopy, broadband ferromagnetic resonance spectroscopy, and Brillouin light scattering spectroscopy are given. The discussion presented in this chapter will serve as a useful resource and reference material for researchers and students working in the field of low-dimensional magnetism and in the broader context of nanotechnology.

Growth and Characterization of Magnetic Thin Film and Nanostructures

A combination high‐sensitivity alternating current (ac) susceptometer and high‐frequency B–H looper is described. Based on the well‐known inductance technique, the design uses modern low‐noise components and stable temperature control to achieve the high sensitivity. The mechanical assembly is designed for use inside a glass Dewar, enabling measurements to be made at any temperature between 4.2 and 300 K. Initial ac susceptibility can be measured over a frequency range of 10 Hz to 120 kHz with sensitivity of 1×10−8 emu, comparable to a superconducting quantum interference device (SQUID) magnetometer. B–H loops are measured at 2 kHz with a low duty cycle, damped oscillatory field pulse, and have sensitivity of 4×10−8 emu. The instrument can thus measure ac susceptibility at higher frequencies than ac‐equipped SQUID magnetometers and commercially available inductive ac susceptometers, and can also measure B–H loops at much higher frequencies and with greater applied fields than steady‐state loop tracers.

Combination high-sensitivity alternating current susceptometer and high-frequency b-h looper

An instrument for measurement of the magnetic properties of samples of small cross‐sectional area is described. The signal from two opposed pick‐up coils, one of which contains the sample, is integrated, amplified, and applied to the vertical deflecting plates of a cathode‐ray oscillograph. Each of the pick‐up coils lies in one of a pair of identical magnetizing solenoids. The signal from a non‐inductive resistance in series with the solenoids provides the horizontal deflection for the cathode‐ray oscillograph so that the hysteresis loop of the sample is displayed on the fluorescent screen. The instrument is well suited for measurement of the magnetic properties of samples having cross‐sectional areas of the order of magnitude of 10−5 cm2.

Eugene C. Crittenden

Papers

B–H Meter for Samples of Small Cross‐Sectional Area