# Presentation: 161404

## Weak Localization of Itinerant Electrons in FerromagnetsArthur F. Hebard, University of Florida, DMR 0404962

**Weak Localization of Itinerant Electrons in Ferromagnets****Arthur F. Hebard, University of Florida, DMR 0404962**

**S****ample ****H****andling ****I****n ****VA****cuum (****SHIVA****) Deposition Chamber**

- A novel one-of-a-kind vacuum chamber (SHIVA) has been constructed which allows the transfer (without exposure to air) of freshly deposited ultra-thin air-sensitive films into an adjacent cryostat for measurements at low temperatures and high magnetic fields. We have used this capability to study magnetotransport and the Hall effect in a series of disordered iron films with thicknesses on the order of 10-100 Å. Detailed temperature and magnetic field dependent studies show that the itinerant electrons, which are spin aligned and hence responsible for the magnetism of iron, become weakly localized and hence more constricted in their motion. Such effects were not expected to be seen in magnetic metals such as iron because the presence of magnetic fields tends to scramble the coherent interactions between electrons that give rise to the localization effect.

**Notes:**
Abstract and title for non-scientific audience* 

Electrons in ferromagnets invited to the quantum dance!
Condensed matter physicists have for a long time been intrigued by the manner in which electrons in metals assume a quantum wave-like character as the temperature is lowered. This character trait becomes manifest when electrons remember their travels and interfere with themselves, much like water waves building up in amplitude when suitably channeled. The resulting tendency of the electrons to stay in one place, or equivalently to be “localized”, causes an increase in electrical resistance that has a non-classical quantum origin. This signature quantum resistance is easily observed in ordinary metals but is not expected to be present in magnetic metals (i.e., ferromagnets) such as iron, since intrinsic magnetic fields severely compromise the ability of the electrons to self interfere. Contrary to these expectations, this paper shows that electrons in ferromagnets can behave much like their brethren in ordinary metals and execute a dance in which they revisit their former coordinates and self interfere. In the experiment, atomically thin films of iron are fabricated and then measured at low temperature and high magnetic field without being exposed to harmful air oxidation. Theoretical analysis takes into account electron-electron interactions and explains the observed localization behavior. 

“Weak localization correction to the anomalous Hall effect in polycrystalline Fe films” , P. Mitra, R. Misra,  A.F. Hebard, K. A. Muttalib and P. Woelfle, Phys. Rev. Lett. 99, 046804 (2007). 

## Weak Localization of Itinerant Electrons in Ferromagnets Arthur F. Hebard, University of Florida, DMR 0404962

- This research has been published in a specialized journal (Physical Review Letters) with a title, *Weak localization correction to the anomalous Hall effect in polycrystalline Fe films*, that is undoubtedly intimidating to a non specialist reader. To increase outreach and make their work more visible to the public, members of our group are encouraged to collaboratively write a PUblic RElations byte (PURE byte) in 200 words or less describing their work in layman’s terms and using a title that will entice the attention of even the most casual reader. A PURE byte is essentially an abstract for a non-technical audience, but like a sound bite, must be brief, catchy and informative. For example, the PURE byte submitted to the University of Florida’s public relations department with the title, “*Electrons in ferromagnets invited to the quantum dance”*, was translated to “*Physicists: Quantum dance draws unexpected guests”* and published as a University news release*****. Writing PURE bytes provides students with an opportunity to practice outreach and gain perspective on the relevance of their own work.

*Outreach with **PU**blic **RE**lations **bytes** (**PURE bytes**)*

***** _[http://news.ufl.edu/2007/07/30/quantum-dance-party/](http://news.ufl.edu/2007/07/30/quantum-dance-party/)_

**Notes:**
First drafts of additional PURE bytes on work supported by this grant:

PURE byte #1
Abstract and title for non-scientific audience*
Anisotropy in thin films: A new direction!
Conventional electrical measurements of conducting thin films fabricated on insulating substrates are only sensitive to in-plane currents that are forced to flow parallel to the film interfaces. Accordingly, there is a critical lack of information about perpendicular electrical transport in strongly correlated electronic materials, such as manganites and high-Tc superconductors, which have anisotropic (direction-dependent) properties due to atomic layering and/or substrate-induced strain. We show that incorporation of an anisotropic manganite film as the base layer of a three-layer capacitor configuration allows simultaneous measurement of electrical transport in both perpendicular and parallel directions. This unconventional technique advantageously employs the simultaneous measurement of dc resistance to extract the in-plane properties and ac capacitance to extract the out-of-plane properties. The information uncovered confirms separate anisotropic percolation transitions that reflect temperature and magnetic field dependent competition between insulating and metallic magnetic phases of the manganite film. In addition, we find a very striking length scale invariance in the distribution of the insulating and metallic phases.
* “Colossal magnetocapacitance and scale-invariant dielectric response in phase-separated manganites”, Ryan P. Rairigh, Guneeta Singh-Bhalla, Sefaatin Tongay, Tara Dhakal, Amlan Biswas and Arthur F. Hebard, Nature Physics 3, 551 (2007), cond-mat/0703046.

PURE byte #2
Abstract and title for non-scientific audience*
Building new walls on a magnetic landscape
To reduce magnetostatic energy, a ferromagnetic metal such as iron forms domains of aligned spins separated by domain walls. The domain walls are metallic regions, typically one micron in width, which manifest gradual changes in spin orientation to accommodate the transition between misaligned spins of neighboring domains. In ferromagnetic manganites, the domain walls can comprise an insulating phase which coexists with the metallic magnetic phase. Our measurements on sub-micron width manganite constrictions show that these insulating domain walls have record-high resistances and can be as thin as a few atomic layers, thus allowing quantum-mechanical tunneling of spin-aligned electrons between adjacent antiparallel domains.
* “Intrinsic Tunneling in Ferromagnetic Perovskites”, Guneeta Singh-Bhalla, Sinan Selcuk, Tara Dhakal, Amlan Biswas, Arthur F. Hebard, submitted to Nature, archive reference: arXiv:0707.4411.