Pulsed Field Magnetometer Research Articles

Nanosecond magnetization reversal in nanocrystalline magnetic films

This paper reports on the investigation of dynamic magnetization reversal process in electrodeposited nanocrystalline Ni and Ni80Fe20 films by employing nanosecond magnetic pulse technique. The surface morphology has been investigated using SEM, EDAX, XRD and AFM analyses and static magnetic properties of the films are characterized by vibrating sample magnetometer (VSM). Two different techniques are designed and employed to study the nanosecond magnetization reversal process in nanocrystalline thin films: Magneto-Optical Kerr Effect (MOKE) and nanosecond pulsed field magnetometer. Results of dynamical behavior as a function of several variables such as magnitude of applied bias magnetic field, amplitude and width of the pulsed magnetic field are analyzed in detail using both techniques. A computer simulation package called Object Oriented Micro-Magnetic Framework (OOMMF) has been used to simulate the magnetic domain patterns of the samples.

A new system for local area measurements in a pulsed field magnetometer

This paper describes a new measuring system to perform local area magnetization measurements on the surface of a magnetic sample in a pulsed field magnetometer at room temperature. A commercial point pick-up coil is used to detect the induction signal along the radius of samples with cylindrical or disc shapes. The relationship between the induced voltage and the sample geometry is treated and a calibration procedure is proposed to obtain the magnetization values in physical units for the case when the point pick-up coil is at the centre of the sample. The local demagnetizing factor is obtained using the measurement of the local anisotropy field applying the single-point detection (SPD) technique. The measurement of this SPD singularity detected in the transverse reversible susceptibility, using a sample with cubic geometry, is demonstrated for the first time in this type of magnetometer. The application of the system for the investigation of commercial permanent magnets is illustrated, and the advantages and disadvantages are discussed.

Coercivity and magnetic viscosity in mechanical milled nanocrystalline YCo5

High coercivity and magnetic viscosity in nanocrystalline YCo5 alloy were observed. The alloy was obtained by arc-melting the raw materials, mechanical milling for 4h with subsequent heat treatment for short times at 1103K and a final quenching in water. The x-ray diffraction pattern showed a single hexagonal 1:5 phase. The average crystallite size determined by transmission electron microscopy was 13nm. Magnetic measurements were carried out at 85K in a pulsed field magnetometer varying the field in the range 50–250kOe and keeping the pulse duration equal to 0.3s. A maximum coercivity of 50kOe was measured when applying a maximum magnetic field of 250kOe. The viscosity parameter was measured varying the dH/dt rate in the range 511–1113kOe∕s. The calculated activation volumes from viscosity data were smaller than the crystallite volume from transmission electron microscopy, consistent with their different physical meanings.

Improved Repeatability of Pulsed Field Magnetometry Measurements Through Peltier Effect Temperature Control of Measurement Coils

Pulsed Field Magnetometers (PFMs) offer a method for high speed full loop characterisation of hard magnetic materials. As there is no dependency on iron to close a circuit, the repeatability of the technique is good. By utilising Peltier effect techniques to control the temperature of the measurement coil systems employed in a Pulsed Field Magnetometer, the level of repeatability of measurements can be significantly improved.

희토류 영구자석의 자성측정을 위한 고감도 펄스마그네토미터

8 MA/m급 펄스자석과 픽업코일, 아날로그 전자적분기, 계수기록형 오실로스코우프, 퍼스널컴퓨터 등을 이용하여 펄스고자장하에서 자성을 정밀 측정할 수 있는 펄스마그네토미터를 구성하였다. 픽업코일은 작은 공간에서 정밀측정이 가능하도록 3-축보상원리를 채용하여 제작하였으며 펄스자장에 대한 신호 보상은 <TEX>$10^{-6}$</TEX>수준이었고 적분기와 오실로스코우프를 거친 후의 최종 자기모멘트의 측정감도는 <TEX>$5{\cdot}10^{-7}\;Am^2$</TEX>이었다. 본 실험을 통하여 구성된 펄스마스네토미터는 지름 <TEX>$3\;mm{\phi}$</TEX>, 이하의 소형 및 박막형 희토류 영구자석의 특성평가에 적합하였다. A 8 MA/m-class pulsed field magnetometer has been constructed by composing a pulsed field magnet, a pickup coil, analog integrators, a digital storage oscilloscope and a personal computer. For precision measurements, a 3-axis compensation principle has been applied for the fabrication of pickup coil, and the compensation level of the order of <TEX>$10^{-6}$</TEX> and the sensitivity of <TEX>$5{\cdot}10^{-7}\;Am^2$</TEX> for magnetic moment have been obtained. The high sensitivity of the magnetometer is good enough for measurements of magnetic properties of rare earth magnets in small size or thin films shorter than <TEX>$3\;mm{\phi}$</TEX> in diameter.

A pulsed field magnetometer for the measurement of small sized permanent magnets

A pulsed field magnetometer with maximum field of 8 MA/m has been constructed by applying 3 axis compensation and analog integration techniques. The m-coil homogeneity, calibration, measurement sensitivity and sample loading problem have been examined. Using the magnetometer full magnetic characterisation of a small sized NdFeB magnet was performed satisfactorily. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of time dependent effects in the magnetization processes of YxSm1−xCo3Cu2 alloys

The magnetic viscosity coefficient in YxSm1−xCo3Cu2 alloys, with x=0, 0.25, 0.5, 0.75, and 1, was determined from measurements of the magnetization reversal relaxation close to the coercive field using a vibrating sample magnetometer and from the coercive field relaxation by the sweep-rate method using a pulse-field magnetometer, respectively. The coercive field and the magnetic viscosity coefficient, as determined from both methods, decrease with increasing yttrium concentration. However, the magnetic viscosity coefficient obtained from magnetization relaxation is always smaller (about six times) than that obtained by means of pulsed field measurements. These results are explained on the basis of different time windows of the measurements, proving different flat distributions of energy barriers due to a complex distribution of activation energies.

Generation, measuring technique and application of pulsed fields

The aim of this work is to give an overview of reproducible pulsed field techniques. Special emphasis is laid on magnetization measurements. A calibration method well suited for pulsed field magnetometers will be described. Pulsed fields can be used for measuring not only the magnetization but also the magnocrystalline anisotropy, and the complete hysteresis loop of permanent magnets can be determined as well.

A study of La-substituted strontium hexaferrite by hydrothermal synthesis

The possibility of replacing Sr by La and Fe by Co and the subsequent improvement of the magnetic properties of the M-type ferrite stimulated our interest in studying other rare-earth ion substitutions. We have found that Sm and Nd substitutions can increase the coercivity of the hydrothermally synthesised Sr hexaferrite powder without causing any significant fall in the saturation magnetisation. In the present work, La-substituted Sr hexaferrite particles were prepared by hydrothermal synthesis and subsequent calcinations. The effects of the initial La/Sr ratio and the calcination temperature on the structure, particle morphology and magnetic properties of La-substituted Sr hexaferrite were investigated by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometry and a pulsed field magnetometer. It was found that, under hydrothermal conditions, the La 3+ additives did not substitute exclusively into the SrM structure but this could be achieved to a greater extent by subsequent calcinations at high temperatures. Compared to the effect of Sm and Nd substitutions, La substitution only increases slightly the coercivity for the samples with initial La/Sr ratios up to 1/8, and for the samples with La/Sr ratios such as 1/4 and 1/2, the coercivity is smaller than that of the sample without La. This can be attributed to grain growth during calcination. Most of the La-substituted samples exhibit a similar magnetisation to that of SrFe 12O 19.

A pulse field magnetometer for local magnetization measurements

A pulse field magnetometer with a new flat pick-up coil device is presented for the characterization of magnetic materials in high magnetic fields. The dimensions of this pick-up coil allow the registration of local hysteresis loops. Magnetization measurements and anisotropy field measurements were performed locally on Nd-Fe-B and M-type ferrite permanent magnets at room temperature. Estimation of the local demagnetizing factor by the measurement of H A using the SPD technique is presented. Local hysteresis loops show the eddy current effect in conducting magnetic metallic samples. The field calibration with the surface coil is also discussed.

The characterisation of magnetic pigment dispersions using pulsed magnetic fields

In this work, we describe the application of pulsed field magnetometry techniques for the characterisation of magnetic pigment dispersions. Magnetic pigment dispersions are important technological materials as in one form they are the material which are used to coat base film in order to make magnetic recording tape. It is these materials that have been evaluated. In this work, we describe the use of two pulsed field magnetometers, one being a low-field instrument with a maximum field of 750 Oe and the other a high-field instrument with a maximum field of 4.1 kOe. Using inductive sensing, the magnetisation is monitored in real time as the pulse is applied. We find that using these techniques we can successfully monitor the progress of the dispersion process, the effects of different resin systems and the effect of different processing conditions. We find that our results are consistent with rheological and other measurements.

Pulsed field magnetometery for high coercivity permanent magnets

A high sensitivity pulsed field magnetometer for the measurement of thin films or small volume of high coercive rare earth permanent magnets has been constructed. The pickup coil designed in principle of 3-axis compensation has the sensitivity of 5×10−4 emu at tested field of 76 kOe. The compensation has been repeatable within 4×10−4–10×10−4 emu, which is enough for measurement within 2% accuracy for the materials with magnetic moment as small as 5×10−2 emu. Measurements on NdFeB magnet show excellent repeatability within 0.3% discrepancy for remanence and coercivity. The magnetic hysteresis loop of a NdFeB thin film (1050 nm) was measured satisfactorily. Estimation of the eddy current effect, by measuring the similar dimensioned but lower resistive nonmagnetic metals, has also been investigated.

Calibration of an industrial pulsed field magnetometer

Summary form only given. Based on the existing knowledge an industrial pulsed field magnetometer (PFM) was developed focusing on the industrial needs. The system shall be used for characterizing the hysteresis parameters (coercivity, remanence, energy product) of permanent magnets. The purpose is two use a fast and reliable magnetometer for the quality control but also in a later step as a standardized measurement method for magnets. For this purpose the best suited setup but also effects like that of eddy currents in such transient fields were studied in the past. It is the purpose of the present work to investigate a high accurate calibration procedure for such pulsed field magnetometers.

Pulsed field magnetometer for industrial use

Summary form only given. An industrial Pulsed Field Magnetometer (PFM) was developed, focusing on industrial needs. The system is to be used for the complete characterising of permanent magnets in a production line situation. The purpose is to create a fast, reliable and accurate magnetometer for quality control but also, in a later step as a standard measurement method for magnets.

Eddy currents in pulsed field measurements

The eddy-current magnetization of spherical and cylindrical samples of technical Cu and Al were measured in a pulsed field magnetometer using different pulse durations τ=9.1 and 15.7 ms. Good agreement between the measured eddy-current moment as a function of the applied field with that calculated by a finite element program was found.

A pulsed field magnetometer for the qualitiy control of permanent magnets

A pulsed field magnetometer (PFM) for industrial applications was developed. The system has a capacitor bank of 5 mF for energy storage, which can be charged up to 3000 V. The pulse magnet has a bore of 30 mm (including the pickup coil), which is subdivided into two coils and produces a maximum field of 5 T with pulse frequencies of 17.5 and 25 Hz. The magnetisation is measured with a well balanced and temperature stabilised coaxial pickup system. The signal is integrated with a stable analogue integrator with selectable time constants. The signals are connected to a 14bit 5M sample/s two-channel ADC in a computer. For the data handling a C ++-based computer program was written. The effects of eddy currents on the metallic samples are corrected by using the so-called f/2 f method. Here two hysteresis measurements with two different time constants are used to measure the eddy current error. The function and reliability of the system is demonstrated by measuring the hysteresis of standard permanent magnets in the PFM and in a static system.

Finite element modeling of permanent magnets under pulsed field

This paper describes a mathematical approach for modeling the eddy current effects in permanent magnets under pulsed field. This approach is particularly useful for designing and optimizing pulsed field magnetometers, which are widely used for complete characterization of permanent magnets. The scheme is based on a transient finite element model and it takes into account the real texture of the permanent magnet. Numerical examples are presented to validate the method.

Measurement accuracy of a pulsed field magnetometer designed for rare earth based permanent magnets

A pulsed field magnetometer with maximum field of 120 kOe has been constructed. The pulsed field generated by a 18 kJ capacitor bank system combined with a pulsed coil was oscillation damped with a period of 10.12 ms. The specimen space was designed to heat up to 200/spl deg/C by flowing hot N/sub 2/ gas. Magnetic hysteresis curve was measured by induction method during 10.12 ms of a pulsed duration from the first positive to the second positive peak. The accuracy of PFM is 2% within the space of /spl plusmn/2 mm/spl times/8 mm at the center of the J-coil.

Pulsed field magnetometer for low-temperature study of high-performance permanent magnets

A pulsed magnetometer is useful for testing high-performance magnets because it can produce high magnetic fields that are sufficient to magnetically saturate them. We installed a cryostat in a pulsed magnetometer and tested several prevailing permanent magnets at low temperatures. The measurements were successfully performed down to 4.2 K, and it was shown that a pulsed magnetometer is useful for low-temperature measurement on permanent magnets as well as room-temperature measurements.

Giant magnetic viscosity in SmCo5−xCux alloys

Hysteresis loops in SmCo5−xCux as-cast and annealed magnets (1&amp;lt;x⩽3) were measured at room temperature using a pulsed-field magnetometer and a static vibrating sample magnetometer. At field sweeps between 2 and 17 (GA/m)/s a giant—in this field range nearly constant—magnetic viscosity Sv was obtained. The viscosity is approximately proportional to the Cu concentration and to the coercive field. A heat treatment at 1273 K for three weeks changes the microstructure and enhances strongly the intensity and the time dependence of the coercivity. The decay of the inverse of the coercive field Hc with time follows a simple ln(t) relation between 10−5 and 10 s. Data analysis allows a density of stacking faults N to be extracted for each sample. Sv (and Hc) increases with N which increases with x.