Research Interests

Antiferromagnetism in thin Cr films

 

Bulk Cr

 

 

Bulk chromium orders below the Néel temperature of TN = 311 K as an incommensurate spin-density wave antiferromagnet. The wave vector q of the SDW is parallel to one of the <100> directions and the polarization S of the Cr magnetic moments is perpendicular to q, what is called a transverse spin-density wave (AF1 structure). Below the spin-flip temperature TSF = 123 K the stable phase switches from the transverse to a longitudinal spin-density wave with S parallel to q, the so-called AF2 structure.

 

Thin Cr films

The magnetic behaviour of thin Cr films deviates from the bulk properties mainly due to size effects, epitaxial strain, and exchange coupling at the interface. The aim of the experiments is to understand the influence of all these factors on the antiferromagnetism of thin Cr films.

We have performed a detailed neutron diffraction study on (110) oriented Fe/Cr multilayers as well as V/Cr multilayers to compare directly the proximity effects of a paramagnetic with a ferromagnetic layer. The neutron diffraction experiments benefit from the fact that for a bcc crystal the reflections with h+k+l = odd are structurally forbidden. So, the Cr{100} reflections are of pure magnetic origin. This is also valid for a body centered tetragonal structure.

We studied the influence of temperature and magnetic field on the phase diagram by neutron diffraction and determined the epitaxial strain in the Cr films by XRD measurements.

 

 

 

 

Results on V(110) / (1.2 nm Fe / 26 nm Cr)15

The stable phase at room temperature is the commensurate AF0 structure with a Néel temperature of about 520 K and a transition to the incommensurate phase at 200 K. More details can be found in:

D. Aernout, C. L'abbé, M. Rots, H. Fritzsche, and J. Meersschaut
Dynamical magnetic properties of Cr in an Fe/Cr(110) multilayer
Phys. Rev. B 73, 134419 (2006)

H. Fritzsche, S. Bonn, J. Hauschild, J. Klenke, K. Prokes, and G. J. McIntyre

Antiferromagnetic order of thin epitaxial Cr layers in an Fe/Cr(110) multilayer

Phys. Rev. B. 65 , 144408 (2002)

H. Fritzsche, J. Hauschild, T. Nawrath, A. Hoser, S. Welzel, H. A. Graf, and H. Maletta

Spin density waves of thin Cr layers in Fe/Cr(110) multilayers

Physica B 276-278 , 590 (2000)

 

The easy axis of magnetization is the [001] direction. When rotating the Fe magnetization from the easy axis into the in-plane hard-axis direction [1 -1 0] by applying a magnetic field of 0.45 T the intensity of the commensurate Cr(001) peak decreases by a factor of 2. This can be interpreted as a simultaneous rotation of the Fe and Cr moments pinned together in its initial perpendicular orientation and shows the strong exchange coupling at the Fe/Cr interface. More details in:

H. Fritzsche, J. Hauschild, A. Hoser, S. Bonn, and J. Klenke

Perpendicular pinning of Cr magnetic moments to the Fe magnetization in Fe/Cr(110) multilayers

Europhys. Lett. 49 , 507 (2000)

 

Results on MgO / ( 5 nm V / 30 nm Cr)13

In this sample no phase transition from the commensurate to the incommensurate phase is observed. The AF0 structure is visible in the temperature range from 2 K to 550 K. More details:

H. Fritzsche
Antiferromagnetic structure of thin Cr(110) films in large magnetic fields
J. Magn. Magn. Mater. 302, 160 (2006)

H. Fritzsche, S. Bonn, J. Hauschild, K. Prokes, and J. Klenke

Suppression of incommensurate spin-density waves in thin epitaxial Cr(110) layers of a V/Cr multilayer

Eur. Phys. J. B 36, 175 (2003)

 

S. Bonn, H. Fritzsche, J. Hauschild, J. Klenke, H. Maletta

Spin density waves of thin epitaxial Cr(110) layers in a V/Cr multilayer

Appl. Phys. A, 74 [Suppl.] , S932 (2002)