ferromagnetism in hpht c 60 polymers: magnetic carbon or magnetic impurities? alexandr talyzin, (...

Ferromagnetism in HPHT C60 polymers: “magnetic carbon” or

magnetic impurities?

Alexandr Talyzin, (Department of Physics, Umea University, Sweden)

A.Talyzin, Umea University, Sweden

1. History of “magnetic carbon”. Questions?

1996, 1998, 2000- Synthesis of 3 sets of samples. Metallic conductivity in high pressure polymer of C60 (Makarova et al. Synth. Met. 121, (2001).)

2001- Pressure polymerized C60 is intrinsically ferromagnetic (as occasionally discovered) Makarova et al., Nature 413, 716-718, (2001)2002-2004 – four experimental papers confirming ferromagnetism of high pressure polymers of C60 (from two groups)2002-2006- about 15 theoretical papers aimed to explain high temperature ferromagnetism of C60 polymers. 2005- “Ferrocarbon”: EU project aimed on study of “Magnetic Carbons”.

August 2005 – Corrigendum to original paper on “magnetic carbon” is published in “Nature”30 March 2006 – The Nature paper is retracted by 7 authors out of 9 citing results presented below. Two authors (T.Makarova and P.Scharff have not joined retraction).

Polymeric C60- “magnetic carbon”?

Figure by T.Makarova,2003- 2005.

Summary of discovery (Makarova et al,

Nature,2001), five main arguments:

1. Synthesis temperatures close to the point of C60 collapse.

P=6 GPa, T=1025-1050K

2. Ferromagnetic with Curie T ~500K

3. Reproducible: 3 sets of samples, one of them “specially synthesized” were reported in original Nature paper.

4. Ferromagnetism disappears after thermal depolymerization of samples (700K)

5. 22 ppm level for all ferromagnetic impurities (0.003 emu/g) (30 fold less compared to measured magnetization)

No confirmation (Han et al, Phys.Rev.B, 2005)


5 10 15 20 25 30 35 40

1193K

1093K

1085K

1073K

1053K

983K

953K

923K

Inte

nsi

ty (

arb

.un

its)

Diffraction angle (2)

Over 20 samples synthesized at 3.5 GPa. Structure and samples and synthesis conditions are very close to those from “Nature” samples.

X-ray diffraction from one set of samples synthesized in 2004 and studied bySQUID in Germany (Prof.Esquinazi group)

All samples were diamagnetic (including polymers)

Magnetization traces after subtraction of diamagnetic contribution: 0.0003 emu/g

0.1 emu/g in “Nature”, 2001

Why …?

Ferromagnetism disappears after thermal depolymerisation at 700K (Nature, 2001)

DSC (A) R-phase; (B) Magnetic carbon.with Curie T>800K (Korobov et al, Chem.Phys.Lett, 2003)

Nature: magnetization reversible after heating at 640K for 2 hoursAdv.Mat, 2002: Magnetization is reversibleAfter heating at 800K for 16 hours

The same sample (E17) depolymerized at 2000C (473K) in 2001 (Makarova et all, Carbon).In Nature (2001) depolymerization was reported below 700K

Depolymerisation of C60 polymers occurs at 500-560K (1998).(including photopolymers)

Ferromagnetism can not be assigned to polymeric structure.

How to prove existance of new ferromagnetic material?

Ms=0.1 emu/gIntrinsic ferromagnetism of bananas?

Fe Ms=220 emu/g ~450 ppm (0.045%) of Fe- 0.1 emu/g

Any claim of new ferromagnetic material MUST be provided with impurity concentrations- Fe, Ni, Co

Ideally, analyses should be done on the same sample.

Analysis of starting chemicals is NOT sufficient-final sample must be analyzed

Impurity analysis (Makarova et al, Nature 2001).


-“We have paid great attention to chemical analysis of the pristine material as well as of the polymerized phase. The total amount of magnetic (Fe,Ni, Co) impurities is 22 ppm in the pristine phase”.

-Sample cited in Nature: 3 mg. Impurity analysis mentioned in the paper (atomic absorption spectrometry) required 20 mg.

Contamination introduced during synthesis was not taken into account.

Toroid apparatus used for synthesis of samples (Prof. Davydov group,Troitsk, Russia)

Independent confirmations.1) 2.5 GPa- Makarova et al (Synth.metals, 2003). No impurity analysis was done, no magnetic data shown, Ms= 0.01 emu/g (~50 g/g Fe)

2) 6 GPa- Narozhnyj et al (2003), proceedings, 22 ppm in pristine C60 (with reference to Nature paper).Curie T above 800K, not determined.

3) 9 GPa- Wood et al, (2002).Impurity analysis not presented at all.Only one sample shown to be ferromagnetic.

4) 9 GPa- Chan et al,2005 (the same group as 3) Hydrogen amount determined but notFe, Ni,Co.

None of the papers provided satisfactoryImpurity analysis.

22 ppm (mg/g) for all magnetic impurities? No, 400 ppm.


Re-analysis of “Nature samples”by R.Hohne and P.Esquinazi (Adv.Mat., 2002)

-Iron contamination measured by PIXE (30 m depth): 200- 400 g/g,about 20 times higher than previously reported(enough to explain ferromagnetism)

Only 3 samples were studied by SQUID before submission to “Nature” (one split on two pieces)(figure from Adv.Mat., 2002)

Reproducibility and history of samples.All samples used for “Nature” paper were NOT INTENDED (as stated by Prof. V.Davydov) for studies of ferromagnetism.

-All samples were synthesized prior discovery of ferromagnetism, “specially synthesized set (2000)” as well. First observation of ferromagnetism in March 2001 (Prof.P.Esquinazi).

-Samples were split in 1996,1998,2000 by metallic tools (stated in published papers) and repeatedly touched by unprotected magnet in 2001-2004.

-No precautions against contamination was taken during synthesis, several years of storage and handling of samples.

Video from supplementary materials available on line(Makarova et al, Nature, 2001)

The same treatment until 2004 wasgiven to every new sample…

Amounts of iron in ”magnetic carbon”


Figure from Han et al, Carbon 2003Figure from Spemann et al, (2003),conference proceedings

Particles of tens micrometer size.

ImageJ software shows 2-3% of surface are covered by subsurface particles (counting only sharp ones). (~30 m depth of method).

22 ppm of Fe??

Averaging from PIXE:2-3 m spots, 5 points.

1.370, 100, 200,16.000 and 100 (average 482 g/g)

Hundreds of points required!

Conclusion: no impurity analysis-no intrinsic ferromagnetism

No evidence for intrinsic ferromagnetism in HPHT polymers of C60 .

Additional arguments:

1. Ferromagnetism observed for samples synthesized in short interval of temperatures (1025-1050K)?

2. How to explain 500K Curie T?

How impurity could explain Curie T of 500K?


Fe3C is ferromagnet with Curie Temperature 480-500K

Fe, Nb, W, V are known to induce collapse of C60 with formationof carbides in thin films already at 400K.

Model experiments: Fe+C60 at HPHT conditions

Two samples of C60: mixed with 10% (mass) of Fe and 3% of Fe.Samples subjected to the same P-T treatment as C60 used forpreparation of “magnetic carbon. Uniform size of Fe particles: 2-3 m

Reaction of Fe with C60 at 2.5 GPa and 1040K

35 40 45 50 55

35 42 49

Si

10% Fe

3% Fe

Rel

ativ

e In

tens

ity

Diffraction angle 2

Inte

nsi

ty, a

rb.u

nits

Diffraction angle 2


20 30 40 50

Fe (110)

Rel

ativ

e in

tens

ity

Diffraction angle 2

Pristine C60

/ 10% Fe powder

The same sample after HPHT treatment

Iron peaks disappear after high pressure high temperature treatment. Excess of C60 transforms into polymeric phase.

More deteail XRD: iron transformed into Cementite, Fe3C.Curie T (Fe3C)= 480-500K

Fe2O3+C Fe3O4+C Fe+C Fe3C

Ferromagnetism in C60 polymer/Fe3C mixture (Prof. P.Esquinazi group, University of Leipzig)


Pristine C60/10 % Fe mixture

HPHT treated with 10% FeHPHT treated with 3% Fe

Saturation magnetization of Fe3C at (RT) Ms=128 emu/g.

Expected magnetic moments at saturation due to Fe3C were calculated from known Fe concentrations and masses of samples.

Values calculated for both samples are in agreement with the measured data within experimental error.

Iron do not induce ferromagnetism in in carbon

Comparing C60/Fe3C to ”magnetic carbon”.


Pristine C60/10% Fe mixture

Right axis: two samples of ”magnetic carbon”: E17 (Nature, 2001) and E16 (Adv.Mat., 2002)

Left axis: C60/Fe3C samples obtained at HPHT.

Conclusion: ”magnetic carbon” and C60/Fe3C show nearly identical magnetic properties. Rejected from Phys.Rev.B, Published in Eur.Phys. J B., 2007

Ferromagnetism is found reproducibly only for synthesis temperatures close to the point of C60 collapse?


-Nature (2001)- 6 GPa , only at T=1025K-1050K (just below collapse point 1075K)

-Review paper (Makarova, Semiconductors, 2004) -“about one hundred degrees below point of C60 collapse..” That will be 975K. Out of range.

-Review by Makarova, JMMM, (2003)- “….with maximum at 1075K”, exactly the point of collapse.

-MFM paper (Han et al, Carbon, 2003) only one sample studied, the same as in “Nature”: synthesized at ….P=6 GPa and 1125K Above point of C60 collapse!

-The same study published earlier (Nucl. Instr. and Meth. in Phys. Res. B 210 (2003) 531–536) :P=2.5 GPa and 1125K, this sample could not be Rhombohedral at this pressure.

Verified synthesis conditions for “Nature” samples (Corrigendum, 2005).


Stated in the paper: 6 GPa and 1025-1050K, ferromagnetism only in this “narrow interval of temperatures”, 5 samples ferromagnetic from 3 different sets.

Only three samples were studied by SQUID(Prof. Esquinazi, Germany) prior to paper submission. Only two of them were ferromagnetic:

- “Nature sample” 6 GPa and 975K lowest temperature from all set.

-2.5 GPa and 1125K (1998) both P and T out of reported range.

- 6 GPa and 1025K (2000) Not ferromagnetic.

Corrigendum published in Nature, 2005. Reports minor mistakes in synthesis conditions. Celsius to Kelvin calculation error,mistake with sample labels.

Implications of “new” synthesis conditions


-Only one ferromagnetic sample was true Rhombohedral polymer, synthesis temperature 975K was lowest from all samples. “Narrow interval” of temperatures do not exist.

-Second sample (2.5 GPa and 1125K) was not polymeric and not fullerene:C60 collapses at these temperatures.

-Magnetic properties of these two samples were identical: ferromagnetism could not be connected to fullerenes!

-Curie T of 500K was EVER observed only for these two samples, only one of them true Rh polymer.Next set of samples showed Curie T above 800K (Narozhnyj, 2003).

Summary and Retraction (29 March 2006, Nature)


“..T.L.Makarova and P.Scharff decline to sign this retraction because they do not believe that the earlier results, supported in subsequent studies, are totally invalidated by these findings…”. Claim is based on unpublished data for both magnetization measurements and impurity analysis.

Retraction (2006) signed by : B. Sundqvist, R. Hohne, P. Esquinazi, Y. Kopelevich, V. Davydov, L. S. Kashevarova & A. V. Rakhmanina

Ferromagnetism of high pressure polymers of C60 :

- not connected to polymeric structure- not connected to C60

- not reproduced in new experiments- level of magnetization can be explained by impurities without suggesting “magnetic carbon”. - Curie T of ~500K was ever observed only for two samples and can be explained by Fe3C

Magnetic carbon in meteorite? (Coey et al, Nature, 2002)


Magnetisation measured from graphite nodule reported to be 30% higher compared to magnetisation calculated from mineral composition.

Curie Temperature of “magnetic graphite” : ~500KInterpretation: iron induces ferromagnetism ingraphite. Fe3C is actually named

as mineral composing the meteorite.

Cohenite (typical mineral of metheorites): Fe (Ni,Co)3C- antiferromagnetic or ferromagnetic, not counted in the calculations.

Cementite: (also known in meteorites) Fe3C- ferromagnetic stronger than magnetite.

Cigarette ashes and magnetic meteorites


Thermal demagnetisation of ashes from Bulgarian cigarettes ”Shipka” (N.Jordanova, Journal of Magnetism and Magnetic Materials, 2006). “Camel” and “Marlboro” also studied…Fe2O3 - Fe3O4 - Fe3C reactions occur at temperatures higher than 1020K in processof cigarette burning

Fe3C

Fe3O4

Thermal demagnetisation of ”Magnetic meteorite”, J.M.D. Coey et al., Nature (2002)

Fe must have reacted with carbonat temperatures of meteorite fallingand impuct.

Metallic conductivity in high pressure polymers of C60:result of mistakes in Celsius to Kelvin calculations

Makarova, T. L. et al. Anisotropic metallic properties of highly-oriented C60 polymer. Synth. Met. 121, (2001).Makarova, T. L. et al. Electrical properties of two-dimensional fullerene matrices. Carbon 39, (2001).Okotrub et al, J.Chem.Phys. (2001) –model proposed to explain metallic Rh C60.

Makarova (JMMM), 2004

1075K

1025K

975K

Makarova, (2002)

1025 K

1050 K

1075K

Makarova, (Mol.Mat) 2000

1048K

1073K

1123K

Point of C60 collapse: 1075K (Nature)

More carbon magnets?


- Proton irradiated graphite (Prof. P. Esquinazi group). Impurity analysis presented, interesting subject to study.

-Carbon nanofoam (A.V.Rode, Phys.Rev.B, 2004 ). Impurity analysis presented. Ferromagnetism below 90K

-Chemically etched graphite (A.V.Mombru, PRB, 2005). Impurity analysis presented. Results not confirmed (J.M.D.Coey group, 2006), large Fe particles found in their samples in Umea (K. Han)

- Talapatra et al, Phys.Rev.Lett., 2005: ferromagnetism in nitrogen irradiated Nanodiamonds. Commercial detonation nanodiamonds are always contaminated with metallic alloy catalyst. Impurity analysis not presented.

Questions ?

Acknowledgements:

- Prof. B.Sundqvist, (Umea university).- A.Dzwilewski, samples synthesis (Umea University, Sweden)- Prof. L.Dubrovinsky, facilities for synthesis (Bayreuth University,

Germany)- Prof. P. Esquinazi and A. Setzer and (University of Leipzig, Germany).

SQUID magnetometry measurements.

- Special thanks to Prof. P. Esquinazi for providing us with all available raw data related to C60 ”magnetic carbon” and many discussions.

More details in recent papers:

1. A. Talyzin, A. Dzwilewski, L. Dubrovinsky, A. Setzer, and P. Esquinazi, “Structural and Magnetic properties of polymerized C60 with Fe”. Eu. Phys. J.l B, 2007.

2. A. Talyzin and A. Dzwilewski ,J.Nanoscience and Nanotechnology, Review, April 2007

Increased stability of magnetic carbon to depolymerization?


Depolymerisation of ALL C60 polymers occurs below 600K(including photopolymers).

T.Makarova, Semiconductors, 2004

XRD shown in figure were taken from two different samples, both are not from Rh polymer!

Heated at 800K(2.5 GPa, 1125K)

Pristine polymer(2.5 GPa, 1050K)

Makarova (Semiconductors, 2004):“One of the samples lost only 2% of magnetization, and the X-ray diffraction patterns remained unchanged after annealing and corresponded as before to the rhombohedral phase of polymerized C60.” This sample (E17) was destroyed during heating due to oxygen leak (Prof. Esquinazi)

The same sample (E17) depolymerized at 2000C in 2001 (Makarova et all, Carbon).

In Nature (2001) depolymerization was reported below 700K

ferromagnetism in hpht c 60 polymers: magnetic carbon or magnetic impurities? alexandr talyzin, (...

Documents

synthesis of samples

set of samples

history of samples

sets of samples

magnetic fe

original nature paper

impurity analysis makarova

gpa makarova et