Abstract
Pyrrhotite, Fe7S8, is a common sulfide mineral in the Earth's crust and mantle, as well as in a range of meteorites and is of interest to a wide variety of disciplines including economic geology, geophysics, and material science. The 4C variety of pyrrhotite shows a dramatic change in magnetic properties at T 30 K, known as the Besnus transition. Although this transition is frequently used to detect pyrrhotite in geologic samples, the underlying mechanism driving the transition has not yet been identified. This study presents a high-resolution view of the changes in heat capacity, magnetic, and electronic properties of a natural single crystal of nearly pure, monoclinic 4C pyrrhotite across the Besnus transition. Contrary to previous studies, all of these properties show clear evidence of the Besnus transition, specific heat, in particular, revealing a clear transition at 32 K, apparently of second-order nature. Small-angle neutron scattering data are also presented, demonstrating an unusual change in short-range magnetic scattering at the transition. Furthermore, a magnetic field dependence of the transition temperature can be seen in both induced magnetization and electrical resistivity. These new observations help narrow the possible nature of the phase transition, clearly showing that interactions between intergrown coexisting 4C and 5C superstructures, as suggested in some literature, are not necessary for the Besnus transition. In fact, the changes seen here in both the specific heat and the electronic transport properties are considerably larger than those seen in samples with intergrown superstructures. To further constrain the mechanism underlying the Besnus transition, we identify five separate potential models and evaluate them within the context of existing observations, thereby proposing experimental approaches that may help resolve ongoing ambiguities.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1674-1689 |
| Number of pages | 16 |
| Journal | American Mineralogist |
| Volume | 103 |
| Issue number | 10 |
| DOIs | |
| State | Published - Oct 25 2018 |
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Keywords
- Besnus transition
- heat capacity
- magnetism
- phase transition
- pyrrhotite
- resistivity
- sulfide
Cite this
Changes in physical properties of 4C pyrrhotite (Fe7S8) across the 32 K Besnus transition. / Volk, Michael W; McCalla, Eric; Voigt, Bryan; Manno, Michael A; Leighton, Chris; Feinberg, Joshua M.
In: American Mineralogist, Vol. 103, No. 10, 25.10.2018, p. 1674-1689.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Changes in physical properties of 4C pyrrhotite (Fe7S8) across the 32 K Besnus transition
AU - Volk, Michael W
AU - McCalla, Eric
AU - Voigt, Bryan
AU - Manno, Michael A
AU - Leighton, Chris
AU - Feinberg, Joshua M
PY - 2018/10/25
Y1 - 2018/10/25
N2 - Pyrrhotite, Fe7S8, is a common sulfide mineral in the Earth's crust and mantle, as well as in a range of meteorites and is of interest to a wide variety of disciplines including economic geology, geophysics, and material science. The 4C variety of pyrrhotite shows a dramatic change in magnetic properties at T 30 K, known as the Besnus transition. Although this transition is frequently used to detect pyrrhotite in geologic samples, the underlying mechanism driving the transition has not yet been identified. This study presents a high-resolution view of the changes in heat capacity, magnetic, and electronic properties of a natural single crystal of nearly pure, monoclinic 4C pyrrhotite across the Besnus transition. Contrary to previous studies, all of these properties show clear evidence of the Besnus transition, specific heat, in particular, revealing a clear transition at 32 K, apparently of second-order nature. Small-angle neutron scattering data are also presented, demonstrating an unusual change in short-range magnetic scattering at the transition. Furthermore, a magnetic field dependence of the transition temperature can be seen in both induced magnetization and electrical resistivity. These new observations help narrow the possible nature of the phase transition, clearly showing that interactions between intergrown coexisting 4C and 5C superstructures, as suggested in some literature, are not necessary for the Besnus transition. In fact, the changes seen here in both the specific heat and the electronic transport properties are considerably larger than those seen in samples with intergrown superstructures. To further constrain the mechanism underlying the Besnus transition, we identify five separate potential models and evaluate them within the context of existing observations, thereby proposing experimental approaches that may help resolve ongoing ambiguities.
AB - Pyrrhotite, Fe7S8, is a common sulfide mineral in the Earth's crust and mantle, as well as in a range of meteorites and is of interest to a wide variety of disciplines including economic geology, geophysics, and material science. The 4C variety of pyrrhotite shows a dramatic change in magnetic properties at T 30 K, known as the Besnus transition. Although this transition is frequently used to detect pyrrhotite in geologic samples, the underlying mechanism driving the transition has not yet been identified. This study presents a high-resolution view of the changes in heat capacity, magnetic, and electronic properties of a natural single crystal of nearly pure, monoclinic 4C pyrrhotite across the Besnus transition. Contrary to previous studies, all of these properties show clear evidence of the Besnus transition, specific heat, in particular, revealing a clear transition at 32 K, apparently of second-order nature. Small-angle neutron scattering data are also presented, demonstrating an unusual change in short-range magnetic scattering at the transition. Furthermore, a magnetic field dependence of the transition temperature can be seen in both induced magnetization and electrical resistivity. These new observations help narrow the possible nature of the phase transition, clearly showing that interactions between intergrown coexisting 4C and 5C superstructures, as suggested in some literature, are not necessary for the Besnus transition. In fact, the changes seen here in both the specific heat and the electronic transport properties are considerably larger than those seen in samples with intergrown superstructures. To further constrain the mechanism underlying the Besnus transition, we identify five separate potential models and evaluate them within the context of existing observations, thereby proposing experimental approaches that may help resolve ongoing ambiguities.
KW - Besnus transition
KW - heat capacity
KW - magnetism
KW - phase transition
KW - pyrrhotite
KW - resistivity
KW - sulfide
UR - http://www.scopus.com/inward/record.url?scp=85054588258&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85054588258&partnerID=8YFLogxK
U2 - 10.2138/am-2018-6514
DO - 10.2138/am-2018-6514
M3 - Article
AN - SCOPUS:85054588258
VL - 103
SP - 1674
EP - 1689
JO - American Mineralogist
JF - American Mineralogist
SN - 0003-004X
IS - 10
ER -