ARkival measures the coercivity of magnetic material from a magnetic hysteresis loop measured with a vibrating-sample magnetometer (VSM). Coercivity is measured and reported in Oersted or ampere/meter units and denoted by Hc in the Hysteresis loop. In the VSM measurement, the coercivity Hc is measured by applying a (reverse) magnetic field  to reduce the sample magnetization to zero after the samples has been magnetized to saturation. Coercivity is defined from a Hysteresis loop at the point where H Field has a value at “0”. Ferromagnetic materials with high coercivity are called magnetically hard, and materials with low coercivity are said to be magnetically soft.

ARkival’s Torque Measurements are performed with a MicroSense VSM employing an ultra-low friction, air bearing suspending the sample with virtually zero friction. The resulting torque measurement reports the actual force on the sample. All pre-measurement calibrations are directly based upon a known torque sample. ARkival’s magnetic torque measurements can accommodate solid, bulk, and thin film samples with a torque measurement capability from 0.05 dyne-cm to 500 dyne-cm depending upon the sample magnetics, applied field, sample type and size.

Direct Magnetic torque measurements can, in some samples be more sensitive than SQUID magnetometry as our direct torque measurement is more precise and more sensitive than an indirect vector coil-based torque system.

Whereas torque is a measure of the sample’s magnetic or shape anisotropy, the magnetic torque measurement can detect magnetic phase transitions or quantum oscillations. Under certain conditions, the sample magnetization can also be extracted from the measured torque.

Permeability is the measure of the resistance of a material against the formation of a magnetic field. It is a measure  of the magnetization that a material obtains in response to an applied magnetic field. Magnetic permeability is typically represented by the Greek letter μ. In general, permeability is not a constant value, as it can vary with the position in the medium, the frequency of the applied magnetic field, humidity, temperature, and other criteria. In a nonlinear medium, the permeability can depend on the strength of the magnetic field. Permeability as a function of frequency also addresses real or complex values.

A closely related property of materials is magnetic susceptibility, which is a dimensionless proportionality factor that indicates the degree of magnetization of a material in response to an applied magnetic field.

About Permeability Units

In SI units, permeability is measured in henries per meter (H/m), or equivalently in newtons per ampere squared (N⋅A⁻²). The permeability constant μ₀, also known as the magnetic constant or the permeability of free space, is a measure of the amount of resistance encountered when forming a magnetic field in a classical vacuum.

Until 20 May 2019, the magnetic constant had the exact (defined) value μ₀ = 4π × 10⁻⁷ H/m ≈ 12.57×10⁻⁷ H/m.

On 20 May 2019, a revision to the SI system went into effect, making the vacuum permeability no longer a constant but rather a value that needs to be determined experimentally; 4π × 1.00000000082(20)×10⁻⁷ H⋅m⁻¹ is a recently measured value in the new system. It is proportional to the dimensionless fine-structure constant with no other dependencies.

In 2019, the SI base units were redefined in agreement with the International System of Quantities, effective on the 144th anniversary of the Metre Convention, 20 May 2019. In the redefinition, four of the seven SI base units – the kilogram, ampere, kelvin, and mole – were redefined by setting exact numerical values for the Planck constant, the elementary electric charge, the Boltzmann constant, and the Avogadro constant, respectively.

In electromagnetism, the auxiliary magnetic field H represents how a magnetic field B influences the organization of magnetic dipoles in a given medium, including dipole migration and magnetic dipole reorientation. Its relation to permeability is

where the permeability, μ, is a scalar if the medium is isotropic or a second rank tensor for an anisotropic medium.

Relative permeability and magnetic susceptibility 

Relative permeability, denoted by the symbol  , is the ratio of the permeability of a specific medium to the permeability of free space μ₀:

 4π × 10⁻⁷ N⋅A⁻² is the magnetic permeability of free space.

In terms of relative permeability, the magnetic susceptibility is

The number χ_m is a dimensionless quantity, sometimes called volumetric or bulk susceptibility, to distinguish it from χ_p (magnetic mass or specific susceptibility) and χ_M (molar or molar mass susceptibility).

Demagnetization is a procedure or method used to eliminate unwanted (major or minor) magnetic fields. Demagnetization is also the reduction or elimination of magnetization. The demagnetization procedure can be performed as an automated process done in a VSM to remove residual magnetization resulting from substrate materials, magnetic artifacts, magnetic noise and exchange interactions and the like. The process results in a clearly differentiated ‘before and after’ Hysteresis loop measurement report.

Alternative means to perform demagnetization are to heat the object above its Curie temperature, where thermal fluctuations have enough energy to overcome exchange interactions, the source of ferromagnetic order, and can destroy that order. In some applications and materials an electric coil with alternating current running through it, can also be used to generate alternating magnetic fields that oppose the magnetization.

Application Measurements include Field data and corresponding frequency measurements for inductive coils, transformer coils and windings, flat coils, vapor deposited materials and Automotive device applications, remote communication and remote charging applications.

Using both manual AC testers and/or AC robotic testers ARkival can measure and report AC magnetic fields emanating  from AC sources in both in 2 dimensional and 3 dimensional designs and products. Field reports can be used to substantiate Finite Element calculations and results as well as produced graphic plane-plane reports that include individual field data and frequencies, Magnetic Energy plots and specific point -point Magnetic Energy values.

ARkival calibrates AC field data reporting with a variable Helmholtz coil array designed for AC Field data over different bandwidth specta.

Magnetic saturation is the state reached in a sample when increases in applied external magnetic field H cannot increase the magnetization of the material further. At saturation, the total magnetic flux density B does not increase with increases in applied external fields. Saturation is a characteristic of ferromagnetic and ferrimagnetic materials, such as iron, nickel, cobalt and their alloys.

Saturation is most clearly seen in the Hysteresis loop (above).. As the H field increases, the B field approaches a maximum value asymptotically, denoted as the saturation magnetization of the substance. 

Different materials have different saturation levels. High permeability iron alloys used in transformers reach magnetic saturation at 1.6–2.2 teslas (T), whereas ferrites saturate at 0.2–0.5 T.  Some amorphous alloys saturate at 1.2–1.3 T. Mu-metal saturates at around 0.8 T.

source: Wikipedia

A vibrating-sample magnetometer (VSM) is an accurate scientific instrument used to measure magnetic properties.

A magnetic material sample is first magnetized via a uniform external magnetic field. The sample is then sinusoidally vibrated via linear actuator or a mechanical vibrator. The induced voltage from the magnetized sample is sensed in a close-proximity pickup coil whereby the induced voltage is proportional to the sample’s magnetic moment, which in turn,  is directly dependent on the strength of the applied magnetic field. Typically, the induced voltage is measured via a lock-in amplifier where the output is used to generate the hysteresis curve of a material during the sweep of the applied external magnetic field.

Remanence , remanent magnetization, Retentivity  or residual magnetism is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed. After certain classes of magnet material are “magnetized” they have remanence. The remanence of magnetic materials provides the magnetic memory in magnetic storage devices, and in common magnets or easily magnetized materials. In cases where where Remanence is unwanted, it can be removed by applying a negative inducing field in a proocess often called degaussing.

In magnetic studies and applications, ARkivak measures and reports residual magnetization using a VSM Magnetometer.  The magnitude or strength of the material remanence is used to characterize permanent magnets; Neodymium magnets, for example, have a remanence approximately equal to 1.3 teslas

The default definition of magnetic remanence is the magnetization remaining in zero field after a large magnetic field is applied (enough to achieve saturation).

Source: Wikipedia