ASTM_A_894_-_A_894M_-_00_2011e1.pdf

Designation:A894/A894M00(Reapproved 2011)1Standard Test Method forSaturation Magnetization or Induction of NonmetallicMagnetic Materials1This standard is issued under the fixed designation A894/A894M;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()indicates an editorial change since the last revision or reapproval.1NOTEUpdated 6.3 and 6.3.2 editorially in October 2011.1.Scope1.1 This test method covers the measurement of saturationmagnetization of magnetic materials using a vibrating samplemagnetometer.1.2 Explanation of symbols and abbreviated definitionsappear in the text of this test method.The official symbols anddefinitions are listed in Terminology A340.1.3 The values stated in either customary(absolute(orpractical)cgs-emu)units or SI units are to be regardedseparately as standard.Within the text,the SI units are shownin brackets.The values stated in each system are not exactequivalents;therefore,each system shall be used independentlyof the other.Combining values from the two systems mayresult in nonconformance with this method.1.4 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.Referenced Documents2.1 ASTM Standards:2A340 Terminology of Symbols and Definitions Relating toMagnetic Testing3.Summary of Test Method3.1 The magnetic induction B,magnetic field strength H,and magnetization M in a material are related by the followingequation(1):3B 5 H14Mcgs units!B 5 oH1M!SI units#3.1.1 In this test method,cgs units are given in parentheses()and SI units in square brackets.3.2 The magnetization M is the magnetic moment per unitvolume of material.In a ferromagnetic or ferrimagneticmaterial,M increases with the applied magnetic field H,but atsufficiently high values of H,M approaches a constant maxi-mum value called the saturation magnetization Ms(emu/cm3)or A/m.The corresponding value of B H=4Ms(gauss)orB oH=oMstesla is called the saturation induction.It issometimes given the label Bs.3.3 If a sphere of isotropic magnetic material is placed in auniform magnetic field,the sphere becomes uniformly magne-tized in a direction parallel to the applied field.The magneticfield in the space outside the sphere is exactly that of amagnetic dipole located at the center of the sphere and orientedparallel to the magnetization of the sphere.The strength of thismagnetic dipole is equal to the total magnetic moment of thesphere,which is given by:m 5 Mvemu!orAm2#where:v=is the volume of the sphere,(cm3)or m3.Section 4 describes an apparatus that provides an indicationor reading proportional to the strength of this dipole field andtherefore proportional to the magnetization M of the sample.Ifthe proportionality constant between this reading and themagnetic moment can be established,and if the volume of the1This test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of Subcommittee A06.01 on TestMethods.Current edition approved Oct.1,2011.Published December 2011.Originallyapproved in 1970 as F133.Redesignated as A894.Last previous edition approvedin 2005 as A894/A894M00(2005).DOI:10.1520/A0894_A0894M-00R11E01.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to a list of references at the back ofthis standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 sample is known,the magnetization of the sample is deter-mined.Then if the sample can be shown to be magneticallysaturated,the saturation magnetization is determined.4.Apparatus4.1 The equipment used for the measurement is called avibrating sample magnetometer(2)and is illustrated schemati-cally in Fig.1.The sample is attached to the end of anonmagnetic,nonconducting rod,and placed in a uniformtransverse magnetic field generated by an electromagnet orsolenoid.The sample and rod are oscillated or vibrated in adirection perpendicular to the field.This oscillating drive maybe produced by attaching the end of the sample rod to aloudspeaker cone or a similar electromagnetic oscillator anddriving the loudspeaker coil with an appropriate ac current.Alternatively,the rod may be oscillated by a mechanical crankor cam driven by a small motor.The frequency and amplitudeof the oscillation must be held constant,either by the mechani-cal design of the apparatus or by an appropriate feedbacksystem.The operating frequency is usually chosen in the