Interpretation and analysis of vibrating sample magnetometer (VSM) results - (2022)

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Increasing media storage density continues to be a very active area of research. Magnetic media may be divided into particulate and continuous media.

Particulate media are comprised of small magnetic particles bonded on a plastic tape or disk, the thickness of the magnetic overcoat is typically on the order of 10,000 Å. Since these are single domain particles, the information is stored by inverting the magnetization of some of the particles. Continuous media are metallic thin films, typically a few hundred angstroms in thickness. Particulate media are advantageous in that they are relatively simple to prepare and are chemically stable, however their recording density is relatively low.

Continuous media on the other hand have higher storage densities and the shapes of their hysteresis loops (and hence recording characteristics) may be varied in a controlled way.

Hard and Soft Magnetic Materials

Magnetic materials are classified into two broad categories, soft or hard. Soft magnetic materials are characterized by large permeabilities and very small coercivities, typically less than 1 Oe. Hard magnetic materials are most often used in permanent magnet applications, and are characterized by large saturation magnetizations, large coercivities, typically greater than 10 kOe, and also by large energy products (i.e., BHmax). Intermediate magnetic materials are generally characterized by coercivities on the order of 1 kOe, and these materials are usually used in magnetic media.

Intermediate magnetic materials include; Gamma-Fe2O3, Co80Cr20, Co77Ni10O13, and thin films. The characteristics of any magnetic material, whether it is hard, soft, or intermediate, are best described in terms of their hysteresis loop. The most common measurement method employed for hysteresis loop determinations at ambient temperature is the Vibrating Sample Magnetometer (VSM).

This paper will discuss the utility of the VSM in the characterization of magnetic media materials. We will limit our discussion to longitudinal recording media, i.e., where the magnetization is parallel to the plane defined by the substrate/film. Perpendicular media, where the magnetization is perpendicular to the plane defined by the substrate/film, and magneto-optical materials are currently enjoying considerable research effort because of their potential for increasing areal storage densities.

Vibrating Sample Magnetometer (VSM) Systems

Vibrating Sample Magnetometer (VSM) systems are used to measure the magnetic properties of materials as a function of magnetic field, temperature, and time. They are ideally suited for research and development, production testing, quality and process control. Powders, solids, liquids, single crystals, and thin films are all readily accommodated in a VSM.

Contemporary commercial VSM’s feature virtually automated operation via data acquisition/control and analysis software that runs on a personal computer, thus making the VSM accessible to the non-specialist. This has dramatically increased the utility of this measurement technique in a broad range of measurement applications.

Theory of Operation of Vibrating Sample Magnetometer Systems

If a material is placed within a uniform magnetic field H, a magnetic moment m will be induced in the sample. In a VSM, a sample is placed within suitably placed sensing coils, and is made to undergo sinusoidal motion, i.e., mechanically vibrated. The resulting magnetic flux changes induce a voltage in the sensing coils that is proportional to the magnetic moment of the sample.

The magnetic field may be generated by an electromagnet, or a superconducting magnet. Variable temperatures may be achieved using either cryostats or furnace assemblies. In the context of the current discussion, we will consider electromagnet based systems only, as magnetic media are usually characterized at ambient temperature, and for only moderate field strengths. Tape and thin film samples to 1 inch in diameter may be characterized in the Lake Shore VSM.

The Hysteresis Loop

In the case of a typical recording medium the hysteresis loop gives the relation between the magnetization M and the applied field H. A hysteresis loop of a magnetic recording medium is illustrated schematically in Figure 1.

The parameters extracted from the hysteresis loop that are most often used to characterize the magnetic properties of magnetic media include; the saturation magnetization Ms, the remanence Mr, the coercivity Hc, the squareness ratio SQR, S* which is related to the slope at Hc , and the switching field distribution SFD. The loop illustrated in Figure 1 shows the behavior for the easy axis of magnetization (i.e., in the anisotropy direction). The loop has a rectangular shape and exhibits irreversible changes of the magnetization.

The hard axis loop, where the hard axis is at right angles to the easy axis, is more or less linear and generally hysteresis free, i.e., the magnetization is reversible. Magnetic materials that show a preferential direction for the alignment of magnetization are said to be magnetically anisotropic. When a material has a single easy and hard axis, the material is said to be uniaxially anisotropic.

Interpretation and analysis of vibrating sample magnetometer (VSM) results - (1)

The intrinsic saturation is approached at high H, and at zero-field the remanence is reached. The squareness ratio is given by the ratio of (Mr/Ms) and is essentially a measure of how square the hysteresis loop is.

In general, large SQR values are desired for recording medium. The formal definition of the coercivity Hc is the field required to reduce the magnetization to zero after saturation. The physical meaning of Hc is dependent on the magnetization process, and may be the nucleation field, domain wall coercive field, or anisotropy field.

Hcis a very complicated parameter for magnetic films and is related to the reversal mechanism and the magnetic microstructure, i.e., shape and dimensions of the crystallites, nature of the boundaries, and also the surface and initial layer properties, etc.

S* and SFD are of particular importance in characterizing the magnetic properties of magnetic media. S* is related to the slope of the hysteresis loop at Hc, i.e., dM/dH|Hc= Mr/(Hc(1 – S*)). This is known as the Williams-Comstock construction. For longitudinal recording media there are two important parameters associated with the recording process that are intimately related to S*.

Namely, the maximum output signal depends on Mr, Hc, and S*, and the optimal bias current also depends on S*. The SFD =ΔH/Hc whereΔH is the full width at half maximum of the differentiated curve dM/dH (as illustrated in Figure 1) can be thought of as a distribution function of the number of units reversing at a certain field. For a particulate medium without collective behavior, the SFD has a close relation to particle size distribution because differently sized and shaped particles will reverse at different field strengths.

For longitudinal media the SFD is related to recording parameters such as noise, optimal bias current, and time dependent behavior. Media with high Hc and small SFD are desirable for high density recording.

Remanence Curves

In addition to the full hysteresis loop properties of magnetic media, there has been increased interest in the measurement of remanence curves. Measurement of remanence determines only the irreversible component of magnetization and thus enables the phenomena of switching to be deconvoluted from the hysteresis measurement, which generally includes a reversible component.

There are two principle remanence curves; the isothermal remanence (IRM) and the DC demagnetization curve (DCD). The IRM is measured after the application and removal of a field with the sample initially demagnetized. The DCD is measured from the saturated state by application of increasing demagnetizing fields. Both are illustrated schematically in Figure 2. These remanence curves are of importance because they yield the true SFD for the material. The VSM may also be used to measure the IRM and DCD remanence curves.

Interpretation and analysis of vibrating sample magnetometer (VSM) results - (2)

The remainder of this paper will present magnetic data for thin film magnetic media, thus demonstrating the utility of the Lake Shore VSM for measuring media magnetic properties.

Magnetic Measurements Using the Lake Shore VSM

The Lake Shore VSM features variable-gap electromagnets providing field strengths to over 2 tesla. Experimental flexibility, both in terms of achievable field strengths, and in terms of allowable sample sizes are provided since the gap spacing may be adjusted to maximize either.

Auto-rotation and Vector options facilitate investigations of anisotropy in magnetic media. With the auto-rotation option the sample may be rotated such that the applied field is oriented parallel to either the easy or hard axis of magnetization, or at any angle in between. The Vector option, which includes 2-axis or 3-axis coil sets placed at right angles to one another, permits simultaneous measurement of both easy and hard axis magnetization for fields oriented parallel to either axis. This option also permits the derivation of torque since torque is equal to the cross product of the field and magnetization vectors (i.e., t = M x H).

Data collection is fully automated with Windows based data acquisition/control and analysis software. Broad application versatility is maintained since measurement parameters may be easily defined and controlled. The software automatically extracts any of a number of parameters, e.g., Ms, Mr, Hc, SQR, S*, SFD, etc., directly from the measured hysteresis loop. And, extensive data analysis capabilities are also provided, e.g., derivative (SFD) curves, substrate and paramagnetic background corrections, etc.

Measurement Results

Hysteresis Loops for a Thick Film Disk Material

Figure 3 shows the initial, minor, and major hysteresis loop for a thin film disk material. In the context of the present discussion, the minor loops of magnetic media are sometimes of interest as they relate to modeling of the write process. Taken together with the major loop, the minimum head field strength required to ensure saturation and hence maximum remanence are determined.

Interpretation and analysis of vibrating sample magnetometer (VSM) results - (3)

Figure 4 shows the initial magnetization curve, major hysteresis loop, and also the DCD demagnetization or remanence curve for a flexible magnetic media material.

Interpretation and analysis of vibrating sample magnetometer (VSM) results - (4)

Major Hysteresis Loop for a Flexible Media Material

Figure 5 shows the major hysteresis loop for a flexible media material, and the derivative curves are also illustrated. These derivative curves are directly related to S* and the SFD. Since small SFD’s are desirable, the sharpness and width of these derivative curves are of interest. A narrow and stable switching transition produces a small SFD, and hence the derivative curves yield useful information concerning the magnetic structure of the media, which in turn is related to the microstructure and chemical inhomogeneities in the layer. These parameters are principally related to the deposition process itself.

Interpretation and analysis of vibrating sample magnetometer (VSM) results - (5)

Figure 6 shows the isothermal remanence (IRM) and DC demagnetization (DCD) remanence curves for a flexible media material. Interaction effects may be investigated by analyzing these curves. If the particulate media is characterized by non-interacting particles then a Henkel plot, i.e. IRM(H) vs. DCD(H), will be linear, and the forward and reverse SFD’s will be identical. Deviations from linearity are attributable to the effects of interactions in the system.

Figure 7 shows the Henkel plot corresponding to Figure 6 and Figure 8 illustrates the forward and reverse SFD’s obtained from differentiation of the IRM and DCD curves. Clearly the SFDs are not identical. The extent to which interactions exist in the system are revealed by these types ofΔM vs H curves. A larger interaction yields a largerΔM peak. The use of this type of analysis is becoming increasingly common in the investigation of interaction effects in particulate and thin film media. A strong correlation exists between the form of these interaction effects, and the degree of dispersion of the particles.

Interpretation and analysis of vibrating sample magnetometer (VSM) results - (6)
Interpretation and analysis of vibrating sample magnetometer (VSM) results - (7)
Interpretation and analysis of vibrating sample magnetometer (VSM) results - (8)

Hysteresis Loop for Hard Disk Magnetic Film

Figure 9 shows a hysteresis loop for hard disk CoPt magnetic film deposited on a rigid disk substrate. Critical M(H) loop parameters are indicated in the figure.

Interpretation and analysis of vibrating sample magnetometer (VSM) results - (9)

Figures 10 and 11 show the hysteresis loop and derivative curve, respectively, for a hard disk film sample.

Interpretation and analysis of vibrating sample magnetometer (VSM) results - (10)
Interpretation and analysis of vibrating sample magnetometer (VSM) results - (11)


Selecting a VSM and Future Requirements

There are a number of considerations that come into play when selecting an appropriate VSM. These include; the types of materials that are to be measured, i.e., both intrinsic magnetic characteristics and physical properties and dimensions are important, required magnetic field strength, accessible temperature range, available measurement options, ease-of- use which is largely dictated by the software interface, etc.

Current research trends in magnetic media include the development of perpendicular recording media, magneto-optical materials, the development of pseudo-contact recording techniques, the use of magnetoresistive (i.e., GMR and CMR) multi-layer films for read heads, the use of alternative substrate materials (e.g., glass), and patterned media. Additionally, the superparamagnetic limit is being approached as magnetic film thicknesses are decreased. This trend will force VSM manufacturers to enhance the sensitivity characteristics of their VSM’s.

This paper has discussed some of the more important magnetic properties of magnetic media, their relation to the recording process, and their determination utilizing a Vibrating Sample Magnetometer measurement methodology. The wide spread use of magnetic media materials for audio, video, and data storage systems results in a continual research effort to increase storage densities, and decrease access time.

Advances made possible by materials science, combined with the development of commercially available computer automated characterization tools, such as the VSM will certainly result in significant advances in this area.


How does a vibrating sample magnetometer work? ›

A vibrating sample magnetometer (VSM) operates on Faraday's Law of Induction, which tells us that a changing magnetic field will produce an electric field. This electric field can be measured and can tell us information about the changing magnetic field.

What is VSM characterization? ›

The Vibrating Sample Magnetometer (VSM) by MicroSense is a measurement system to characterize magnetic properties like DC magnetization. Different magnetic fields can be set, depending on the magnet pole gap.

What are the uses of vibration magnetometer? ›

Vibration magnetometer is used for comparison of magnetic moments and magnetic fields. This device works on the principle, that whenever a freely suspended magnet in a uniform magnetic field, is disturbed from it's equilibrium position, it starts vibrating about the mean position.

What is VSM instrument? ›

The VSM is the instrument used to measure the magnetic moment, the most fundamental quantity in magnetism, of solid samples. When a sample material is placed in uniform magnetic field, a dipole moment proportional to the product of sample susceptibility and applied field is induced in the sample.

How do you plot VSM? ›

Vibrating-sample magnetometer (VSM) data (DAT file) in Origin ...

Why do readings on both sides of magnetometer to be taken? ›

The pivot of the magnetic needle may not lie at the centre of the circular scale and the two pointers will show different angular readings. Such error is eliminated by taking the average of the two readings. The magnetic centre and the geometric centre of a bar magnet may not coincide to each other.

What is meant by vibration magnetometer? ›

Vibration magnetometer is used for comparison of magnetic moments and magnetic fields. This device works on the principle, that whenever a freely suspended magnet in a uniform magnetic field, is disturbed from it's equilibrium position, it starts vibrating about the mean position.

How do you measure coercivity? ›

We can measure Coercivity by measuring the external magnetic field required to reduce the material's magnetic field to zero. This is the amount of negative (H) required to reduce (B) to zero, so it is the crossing of the horizontal axis to the left of the vertical axis.

What instrument measures magnetic field? ›

magnetometer,, instrument for measuring the strength and sometimes the direction of magnetic fields, including those on or near the Earth and in space. Magnetometers are also used to calibrate electromagnets and permanent magnets and to determine the magnetization of materials.

What is VSM physics? ›

Vibrating-sample magnetometry (VSM) is a scientific tool that measures magnetic properties. VSM involves vibration of a magnetic material within a uniform magnetic field H, generating an electric current in properly placed sensing coils.

When a magnet of vibration magnetometer is heated? ›

The magnet of a vibration magnetometer is heated so as to reduce its magnetic moment by 19%. By doing this the periodic time of the magnetometer will [MP PMT 2000, 01]

What is the formula for magnetic moment? ›

τ=p×B. The SI unit for magnetic moment is clearly N m T−1. τ=IA×B.

What is the first step in the VSM? ›

The first step in value stream mapping is to create a current state map. This map can help identify waste such as delays, restrictions, inefficiencies, and excess inventories. These are then eliminated in the ideal state map, which gives the organization a working plan to achieve lean efficiency.

What does VSM tool help produce? ›

VSM is a workplace efficiency tool designed to combine material processing steps with information flow, along with other important related data. VSM is an essential lean tool for an organization wanting to plan, implement, and improve while on its lean journey.

What are the first two areas that should be identified in value stream mapping? ›

There are two main types of value stream maps: current state and future state.

What is the output of magnetometer? ›

Description. The Magnetometer block reads the strength of the magnetic field around an Android™ device. The built-in magnetometer sensor on the Android device measures the magnetic field along the X, Y, and Z axes. The block outputs the magnetic field as a 1-by-3 vector in microtesla (μT).

What is the range of a magnetometer? ›

With a measuring range of 2,400 mT, the magnetometer covers a wide range of measuring tasks. The magnetometer has an accuracy of 1%. This makes the magnetometer a very precise measuring device. With a measuring range of 2,400 mT, the magnetometer covers a wide range of measuring tasks.

How is deflection of a magnetometer calculated? ›

Deflection Magnetometer - YouTube

What is a tangent magnetometer? ›

A system composed of a set of photodiodes in a circular arrangement, proposed as an alternative to measure the deflection angle on the needle of the compass. Depending on the photodiode activated the position of the needle is indicated.

How are the magnetic moment of two bar magnets compared without measuring their moment of inertia? ›

Let the two magnets have moments of inertia l1 and I2 and magnetic moments M1 and M2 respectively place the two given magnets one upon the other if fig (a). This combination is called sum combination.It has moment of inertia (l1 + l2) and magnetic moment (M1 + M2).

Is deflection magnetometer in JEE syllabus? ›

No teacher at my coaching institute has even mentioned it, so I think it's not there. If it is there, I'm in for a big ride.....

What is coercivity in VSM? ›

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”.

What is the unit of coercivity? ›

Coercivity is usually measured in oersted or ampere/meter units and is denoted HC.

What is coercivity formula? ›

The coercivity of a bar magnet is 100A/m. It is to be demagnetised by placing it inside a solenoid of length 100 cm and number of turns 50. The current flowing the solenoid will be :- (1) 4A (2) 24 (3) 1A (4) zero.

What is the principle of magnetometer? ›

Based on the principle of Faraday's laws of induction, these magnetometers comprise copper coils wrapped around a magnetic core. The core gets magnetized by the magnetic field lines produced inside the coils and the fluctuations in the magnetic field bring about the flow of electrical currents.

How accurate is a magnetometer? ›

The same magnetometer could have noise of 1pT, and so able to measure 101.000001uT, it remains that there is a 1% error from the true reading. Some magnetometers will reach accuracy at the level of fractions of a percent, and some can reach ppm level of accuracy, in short, magnetometers can be extremely accurate.

What is retentivity and coercivity? ›

Retentivity: The property of the magnetic material to retain magnetism even in the absence of the magnetizing field is known as retentivity or remanence. Coercivity: The magnetizing field (H) needed to demagnetize the magnetic material completely is known as its coercivity.

What is hysteresis loop explain with diagram? ›

The hysteresis loop shows the relationship between the magnetic flux density and the magnetizing field strength. The loop is generated by measuring the magnetic flux coming out from the ferromagnetic substance while changing the external magnetizing field.

What is squid VSM? ›

Superconducting Quantum Interference Device – Vibrating Sample Magnetometer (SQUID-VSM) A VSM is used to measure magnetic moment. The sample is mounted upon a carbon-fibre rod, which is inserted into a helium flow cryostat and sits between two pick-up coils.

When a freely suspended bar magnet is heated? ›

When a freely suspended bar magnet is heated, its magnetic dipole moment decreases by 36 %.

Which one of the following is equivalent to a bar magnet? ›

Hence, bar magnet can be modeled equivalent to a solenoid. Was this answer helpful?

What is the symbol of magnetic moment? ›

τ is the torque acting on the dipole. m is the magnetic moment.

What is the difference between magnetic moment and magnetic dipole moment? ›

They both are the same. The strength of a magnetic dipole, called the magnetic dipole moment, may be thought of as a measure of a dipole's ability to turn itself into alignment with a given external magnetic field.

What is effective magnetic moment? ›

The effective magnetic moment is a convenient measure of a material's magnetic properties because it is independent of temperature as well as external field strength for diamagnetic and paramagnetic materials.

Do phones have magnetometers? ›

A system called Pulse uses the magnetic field sensor, or magnetometer, for the compass app in iPhones and Android phones, to receive messages in the form of a varying magnetic field produced by a nearby electromagnet.

What is a deflection magnetometer? ›

Deflection Magnetometer-This is a device which is used to measure the magnetic moment and polar strength of a bar magnet. It consists of a very small magnet or a magnetic needle piovoted on a sharp support and free to rotate in a horizontal plane.

What is EMU G? ›

The term emu is short for 'electromagnetic unit' and is not a unit in the conventional sense. It is sometimes used as a magnetic moment (1 emu = 1 erg G−1) and sometimes takes the dimensions of volume (1 emu = 1 cm3). Quantity. symbol. SI unit.

What is hysteresis loop explain with diagram? ›

The hysteresis loop shows the relationship between the magnetic flux density and the magnetizing field strength. The loop is generated by measuring the magnetic flux coming out from the ferromagnetic substance while changing the external magnetizing field.

How do I check the magnetometer on my phone? ›

Check the “Sensors” section under “Features”. If it doesn't mention a magnetometer or compass sensor you probably don't have one. If your device doesn't have a magnetometer, you still might be able to use a compass app which works via GPS – check for this in the app description.

How do I check the magnetic field in my house? ›

Put a material in a magnetic field. Run a current through this material. The magnetic field will create a "sideways" change in electric potential across the material - which you can measure. Using this change in potential and the size of the material, you get the magnitude of the magnetic field.

Why is there a magnetometer on my phone? ›

Compass functionality in phones and tablets is enabled by something a bit more sophisticated – a sensor called a magnetometer, which is used to measure the strength and direction of magnetic fields. By analyzing Earth's magnetic field, the sensor allows a phone to determine its orientation pretty accurately.

How do you calculate magnetometer deflection? ›

Deflection Magnetometer - YouTube

How do you calculate magnetic deflection? ›

Here's a brief recap: If a charged particle is moving in a magnetic field (B), then it experiences a force of magnitude: |F| = q |v x B| = qvBsin(theta) where q is the charge of the particle, v is its velocity, B is the magnetic field strength, and theta is the angle between v and B.

What is inverse square law in deflection magnetometer? ›

When the north pole of magnet A and the north pole of magnet B or the south pole of magnet A and the south pole of magnet B are brought closer, they repel each other. COULOMB'S INVERSE SQUARE LAW OF MAGNETISM. Consider two bar magnets A and B as shown in Figure 3.14.

What is the value of 1 emu? ›

The abcoulomb (abC or aC) or electromagnetic unit of charge (emu of charge) is the derived physical unit of electric charge in the cgs-emu system of units. One abcoulomb is equal to ten coulombs.

What is gauss value? ›

One gauss corresponds to 10-4 tesla (T), the International System Unit. The gauss is equal to 1 maxwell per square centimetre, or 104 weber per square metre. Magnets are rated in gauss. The gauss was named for the German scientist Carl Friedrich Gauss.

Is EMU a SI unit? ›

EMU are the same as Gaussian units for magnetostatics: Mx = maxwell, G = gauss, Oe = oersted. SI: Wb = weber, T = tesla, H = henry, N = newton, J = joule.
Table 1.
SI SymbolSI QuantityConversion from EMU and Gaussian Units to SI Units (a)
MMagnetization, volume magnetization1 erg/(G·cm3) = 1 emu/cm3 → 103 A/m
13 more rows
13 May 2019

What causes hysteresis loss? ›

Hysteresis loss is caused by the magnetization and demagnetization of the core as current flows in the forward and reverse directions. As the magnetizing force (current) increases, the magnetic flux increases.

How do you read hysteresis? ›

The Hysteresis loop explained - YouTube

What is the common cause of hysteresis? ›

The phenomenon of hysteresis in ferromagnetic materials is the result of two effects: rotation of magnetization and changes in size or number of magnetic domains. In general, the magnetization varies (in direction but not magnitude) across a magnet, but in sufficiently small magnets, it does not.

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