ASTM_A_883_-_A_883M_-_01.pdf

Designation:A 883/A 883M 01Standard Test Method forFerrimagnetic Resonance Linewidth and GyromagneticRatio of Nonmetallic Magnetic Materials1This standard is issued under the fixed designationA 883/A 883M;the number immediately following the designation indicates the yearof original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the measurement of the ferri-magnetic resonance linewidth and gyromagnetic ratio of iso-tropic microwave ferrites.This test is restricted to sphericalspecimens possessing resonance linewidths greater than 10 Oe796 A/m.1.2 The values and equations stated in customary(cgs-emuand inch-pound)or SI units are to be regarded separately asstandard.Within this standard,SI units are shown in brackets.The values stated in each system may not be exact equivalents;therefore,each system shall be used independently of the other.Combining values from the two systems may result in noncon-formance with this standard.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Summary of Test Methods2.1 Ferrite materials,in general,exhibit at microwave fre-quencies a power loss or absorption which is a function of anapplied DC magnetic field.In many ferrites,this dependence isof a simple form,having a single maximum at some value ofthe magnetic field,which depends on the microwave frequencyand on the specimen shape.For ferrite materials showing thisbehavior,it is useful to characterize the absorption by means ofan effective gyromagnetic ratio and a resonance linewidth.Note that ferrite materials exist for which the absorption has amore complex behavior as a function of DC magnetic field;thismethod is not intended to apply to such materials.2.2 The value of the field for maximum absorption orresonance may be computed in terms of the magnetization ofthe sample,its geometry,the effective gyromagnetic ratio,g,and the test frequency.For the case of a small sphericalspecimen,the dependence on specimen magnetization dropsout and the effective gyromagnetic ratio can be computed fromthe relationship:v 5 gHr(1)where:v=2pf;f=microwave frequency,MHz;andHr=resonance magnetic field strength,Oe A/m.2.3 The second quantity characteristic of the absorption isthe ferrimagnetic resonance linewidth,DH,which for themethod described shall be defined as the separation of the twomagnetic field values at which the power absorbed by theferrite material is one half the maximum absorption.Theperformance obtainable in specific devices such as isolators,rotators,and so forth,is related to the linewidth and gyromag-netic ratio.2.4 This test method of measuring the ferrimagnetic reso-nance linewidth and the gyromagnetic ratio of a ferrite materialuses a cavity perturbation technique,which requires that thespecimen be small compared to one quarter of the wavelengthof the microwave radiation in the sample.Estimation of thiswavelength requires knowledge of the relative dielectric con-stant,k,and permeability,km,of the specimen material underthe conditions of measurement.The relative permeabilitydepends on both the frequency and the magnetic field,but canbe taken as 2 for the resonance condition in a sphere.Thewavelength in centimetres,l,in the specimen is then approxi-mated by the equation:l 5 3 3 104/=k(2)2.5 The absorption in the specimen is measured by deter-mining the changes of power incident on the cavity required tokeep the output power from the cavity at a fixed referencelevel.It is necessary that the microwave frequency be adjustedto cavity resonance for all measurements.The variations ininput power may be characterized by the variations of theattenuation inserted between a monitored source and the cavityto maintain the reference output level.If a0is this attenuatorreading in decibels with no sample present,and aris thisreading for maximum specimen absorption,then the reading1This test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of SubcommitteeA06.01 on TestMethods.Current edition approved Oct.10,2001.Published December 2001.Originallypublished as C 524 63 T.ASTM Test Method F 130 86 was redesignated asA 883 86e1in 1989.Last previous edition A 883 96.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.corresponding to a specimen absorption of half the resonancevalue is given by the equation:a1/25 a01 20 log 2 2 20 log10a02ar/20!1 1!(3)3.Significance and Use3.1 This test method can be used to evaluate materials suchas garnets and so forth for intrinsic loss factors that can be usedin the