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The classic pattern of magnetic "lines of force" described by iron filings.

Magnetism is one of the more mysterious of the materials properties that are familiar from everyday experience. Magnetism arises from the so-called quantum spin of the electrons within a material; the orientation of this spin can be defined in terms of the direction of the axis or rotation. (Actually, the quantum spin of an electron is most properly thought of as associated with an angular momentum, not an actual spinning). The most familiar type of magnetism is ferromagnetism, defined as the state when the relevant electron spins within a material all point in the same direction. This state is most familiar for the simple reason that when a large number of spins all point in the same direction, their magnetic effects add together to produce a noticeable macroscopic magnetic field. In the other main class of magnets, the antiferromagnets, neighboring electron spins point in opposite directions and tend to cancel each other out as regards large-scale everyday magnetic properties.

Publications

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S. Zhang, I. Gilbert, C. Nisoli, G. Chern, M. J. Erickson, L. O'Brien, C. Leighton, P. E. Lammert, V. H. Crespi and P. Schiffer, "Crystallites of magnetic charges in artificial spin ice," Nature 500, 553 – 557 (2013) Abstract/Comments
P. E. Lammert, C. Nisoli and V. H. Crespi, "Gibbsianizing nonequilibrium dynamics of artificial spin ice and other spin systems," New Jour. Phys. 14, 045009 (2012) Abstract/Comments
S. Zhang, J. Li, J. Bartell, X. Ke, C. Nisoli, P. E. Lammert, V. H. Crespi and P. Schiffer, "Ignoring Your Neighbors: Moment Correlations Dominated by Indirect or Distant Interactions in an Ordered Nanomagnet Array," Phys. Rev. Lett. 107, 117204 (2011) Abstract/Comments
J. Li, S. Zhang, J. Bartell, C. Nisoli, X. Ke, P. E. Lammert, V. H. Crespi and P. Schiffer, "Comparing frustrated and unfrustrated clusters of single-domain ferromagnetic islands," Phys. Rev. B 82, 134407 (2010) Abstract/Comments
J. Li, X. Ke, S. Zhang, D. Garand, C. Nisoli, P. E. Lammert, V. H. Crespi and P. Schiffer, "Comparing artificial frustrated magnets: tuning symmetry in nanomagnet arrays," Phys. Rev. B 81, 092406 (2010) Abstract/Comments
P. E. Lammert, X. Ke, J. Li, C. Nisoli, D. Garand, V. H. Crespi and P. Schiffer, "Direct entropy determination and application to artificial spin ice," Nature Phys. 6, 786 (2010) Abstract/Comments
X. Ke, J. Li, C. Nisoli, P. E. Lammert, W. McConville, R. Wang, V. H. Crespi and P. Schiffer, "Energy Minimization and ac Demagnetization in a Nanomagnet Array," Phys. Rev. Lett. 101, 037205 (2008) Abstract/Comments
R. Wang, C. Nisoli, R. S. Freitas, J. Li, W. McConville, B. Cooley, M. S. Lund, N. Samarth, C. Leighton, V. H. Crespi and P. Schiffer, "Artificial 'spin ice' in a geometrically frustrated lattice of nanoscale ferromagnetic islands," Nature 439, 303 – 306 (2006) Abstract/Comments
V. H. Crespi, L. Lu, Y. X. Jia, K. Khazeni, A. Zettl and M. L. Cohen, "Thermopower of single-crystal Nd1-x (Sr,Pb)xMnO3-?," Phys. Rev. B 53, 14303 – 14307 (1996)
K. Khazeni, Y. X. Jia, V. H. Crespi, L. Lu, A. Zettl and M. L. Cohen, "Pressure dependence of the resistivity and magnetoresistance in single-crystal Nd0.62Pb0.30MnO3-δ," J. Phys. Condens. Mat. 8, 7725 – 7729 (1996)
Y. X. Jia, L. Lu, K. Khazeni, V. H. Crespi, A. Zettl and M. L. Cohen, "Magnetotransport properties of La0.6Pb0.4MnO3 and Nd0.6 (Sr0.7Pb0.3) 0.4MnO3 single crystals," Phys. Rev. B 52, 9147 – 9150 (1995)

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

V. H. Crespi : Magnetism