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Topic: What's the magnetic ordering of Samarium (Sm) at room temperature?  (Read 33401 times)

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Offline onemilimeter

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Hello,

I'm little bit confused with the magnetic ordering (at room temperature) of the elements in the periodic table. For example, what is the magnetic ordering (paramagnetic, ferromagnetic, or antiferromagnetic) of pure Samarium (Sm) at room temperature? I found different interpretations as follows:

[1] “Ferromagnetic Materials” DoITPoMS Teaching and Learning Packages (University of Cambridge)
Figure E: Diagram of a periodic table showing elements coloured according to the type of magnetism they show at room temperature.
http://www.doitpoms.ac.uk/tlplib/ferromagnetic/printall.php
The author commented that the content of the article relied (heavily) on the book, i.e. "Magnetic Materials: Fundamentals and Device Applications", Cambridge University Press (2003).


[2] An article from Birmingham Univ said Sm is paramagnetic at room temperature.
Figure 3: A periodic table showing the type of magnetic behaviour of each element at room temperature.
http://www.aacg.bham.ac.uk/magnetic_materials/type.htm


[3] The following article by David Harrison said Sm is ferromagnetic.
http://www.newi.ac.uk/BUCKLEYC/magnet.htm


[4] Wikipedia said Sm is antiferromagnetic.
http://en.wikipedia.org/wiki/Samarium


By the way, I noted that the periodic table (showing the type of magnetic behaviour of each element) found in the Univ Birmingham and Univ Cambridge websites are different from that found in a reference book "Magnetism Fundamentals", by Damien Gignoux et al., Springer (refer to attachment). Therefore, I do not know which periodic table that I should refer to when determing the magnetic ordering of pure elements at room temperature. Kindly advise.


Thank you very much

Warmest regards
« Last Edit: November 18, 2007, 01:52:33 PM by onemilimeter »

Offline Alpha-Omega

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Re: What's the magnetic ordering of Samarium (Sm) at room temperature?
« Reply #1 on: January 21, 2008, 07:35:23 PM »
This is not easy subject matter.  These concepts are very difficult to grasp.  I am going to try and explain it as simply as I can.

OK you are confused with the terminology: 

Sm is magnetic….but it is how it behaves as a magnetic material that is confusing to you because of how those articles put forth their information.  One article is very comprehensive:  http://www.doitpoms.ac.uk/tlplib/ferromagnetic/printall.php.  The others tell you to ignore things like antiferromagnetism...and that cannot be done in order to explain this properly.

An element can be magnetic or non-magenetic.  If it is magnetic it behaves a certain way. If an element is non magenitic it will not adopt any of the listed behviors.

If an element is magnetic it will behave in one or all of these ways depending on surroundings and state:

1) It may exhibit antiferromagnetic behavior
2) It may exhibit ferromagnetic behavior.
3) It may exhibit ferrimagnetic behavior.


All matter is composed of atoms.  Atoms are composed of protons, neutrons, and electrons.  As electrons fill shells they will fill up and then down (they pair up-when they pair they are of opposite spin). 

If all electrons in an atom are paired then a material is said to be diamagnetic, and is actually somewhat repelled by a magnet.

In some atoms all the electrons are not paired.  Because these atoms have unpaired electrons they are said to be paramagnetic and have what are known as magnetic moments.  Any element that is magnetic…is magnetic and will exhibit one or more of those listed behaviors under various conditions.

These magnetic moments mean that the electrons align themselves in a certain way in an applied magnetic field or with no applied magnetic field with a certain orientation. 

With or without an applied magnetic field, magnetic materials will adopt a specific orientation under different conditions (state: molten, solid, and under various conditions low temperature, room temperature, high temperature, etc…) The different kinds of orientation are called:

1) It may exhibit antiferromagnetic behavior
2) It may exhibit ferromagnetic behavior.
3) It may exhibit ferrimagnetic behavior

The first link you point to:  http://www.doitpoms.ac.uk/tlplib/ferromagnetic/printall.php

Shows you the ways the electrons line up in an applied magnetic field or when there is no applied magnetic field..

All non-magentic materials are termed DIAMAGNETIC (all electrons are paired and all pairs have antiparallel spins).

All Magnetic materials are termed:  Paramagenetic, Ferromagnetic, Antiferromagnetic, or Ferrimagnetic.

All magnetic materials may exhibit one or all of these magnetic behaviors under different conditions.

Indeed, Sm is magnetic at room temperature, it is also antiferromagnetic which just means that the electrons align themselves at room temperature with no applied magenetic field with the pattern you see in that article you point to. The net result of the orientation they adopt results in a nonmagnetic orientation.  The culimination is nonmagnetic. There is no NET or overall magnetism.

As your article states: 
“Antiferromagnetism:
Adjacent magnetic moments from the magnetic ions tend to align anti-parallel to each other without an applied field. In the simplest case, adjacent magnetic moments are equal in magnitude and opposite therefore there is no overall magnetisation.”


This basically tells you that the overall effect is there is no overall magnetism. This is simply the orientation the electrons adopt in this magnetic material under certain cinditions (i.e., Sm at room T-ambient T is antiferromagnetic).

Now as a comparison let’s look at iron.  Iron is magnetic. It is also ferromagnetic.  So it adopts the configuration your article shows: 
“Ferromagnetism:
The magnetic moments in a ferromagnet have the tendency to become aligned parallel to each other under the influence of a magnetic field. However, unlike the moments in a paramagnet, these moments will then remain parallel when a magnetic field is not applied (this will be discussed later). “


In ferromagnetic materials (iron, nickel, and cobalt), the spins of neighboring atoms do align (through a quantum effect known as exchange coupling), resulting in small (a tenth of a millimeter, or less) neighborhoods called domains where all the spins are aligned.
When a piece of unmagnetized iron (or other ferromagnetic material) is exposed to an external magnetic field, two things happen. First, the direction of magnetization (the way the spins point) of each domain will tend to shift towards the direction of the field. Secondly, domains which are aligned with the field will expand to take over regions occupied by domains aligned opposite to the field. This is what is meant by magnetizing a piece of iron.

The factors that determine the magnetic property of a material are the configuration of the electrons in the material, the ability of the atoms or molecules in the material to align magnetically, and the alignment of domains or sections in the object. Since alignment is so important in the magnetic properties of materials, liquids and gases are typically not magnetic because their molecules aren't held in place as they are in solids. An exception is in rotating fluids.

Ferrimagnetic materials adopt another type of magnetic ordering.  In ferrimagnets the moments are antiparallel in alignment-BUT THEY DO NOT CANCEL-like in ANTIFERROMAGNETIC materials.

Magnetite is a good example of a ferrimagnetic material Fe3O4. Two of the iron ions are trivalent Fe3+ and one is divalent Fe2+.  The two trivalent ions align with opposite moments and cancel one another.  The net magnetic moment arises from the divalent Fe2+The opposing moments are unequal and a spontaneous magnetization remains.

Finally, addressing the statement that Sm is ferromagnetic:  Samarium and neodynium in alloys with cobalt have been used to fabricate very strong rare-earth magnets. Such magnets have very high coercivity, remanence, maximum energy product.  Note Sm is alloyed to other metals when it exhibits ferromagnetism.
« Last Edit: April 22, 2008, 07:24:00 PM by Alpha-Omega »

Offline jujofields

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Re: What's the magnetic ordering of Samarium (Sm) at room temperature?
« Reply #2 on: April 21, 2008, 01:01:05 AM »
^^^^Wow!  An extremely helpful reply!  Thanks for all your effort :)

Offline Alpha-Omega

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Re: What's the magnetic ordering of Samarium (Sm) at room temperature?
« Reply #3 on: April 22, 2008, 07:24:27 PM »
NP  ;)

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