Transverse Susceptibility
We measure transverse susceptibility (TS) in our lab using a a resonant radio frequency technique based on a tunnel diode oscillator (TDO). This method has been validated by us over the years to be an excellent probe of the dynamic magnetic response and, in particular, the anisotropy. In this technique, a small fixed amplitude (<5 Oe) RF (10 MHz) field is applied parallel or perpendicular to to the variable external dc field and the parallel (chip) and transverse (χT) components of susceptibility can be independently resolved. Since the sample is placed in an inductive RF coil that is part of a self-resonant circuit, the shift in the resonant frequency with varying dc field and/or temperature gives a direct measure of the change in inductance and thus the sample susceptibility.
Schematic of the TDO-based TS measurement geometry. Drawing of the TDO probe.
The sample is placed in a gelcap that fits in the inductive coil. The coil is part of a multifunctional probe integrated into our Physical Properties Measurement System which provides the dc field and the the variable temperature.
Typical graphs of the transverse susceptibility versus magnetic field of a sample shows peaks at the switching and anisotropy fields of the sample. For thin films and structurally anisotropic materials, these peaks are highly independent of their orientation within the gelcap. How these peaks shift with field and temperature gives insight into the fundamental nature of these magnetic systems.
The difference in the parallel (χP) and transverse susceptibility (χT) for iron nanoparticles. The TS data show distinct peaks associated with the effective anisotropy fields.
Relevant Publications
“Magnetic anisotropy in CrO2 and epitaxial CrO2/Cr2O3 bilayers” –N. A. Frey, S. Srinath, H. Srikanth, M. Varela, S. Pennycook, G. Miao and A. Gupta, Physical Review B (submitted, 2006))
“Magnetic properties of polydisperse and monodisperse NiZn ferrite nanoparticles interpreted in a surface structure model” –R. Swaminathan, M. McHenry, P. Poddar and H. Srikanth, Journal of Applied Physics 97, 10G104 (2005)
“Observation of charge ordering and the ferromagnetic transition in single crystal LSMO using RF transverse susceptibility” –G. T. Woods, P. Poddar, H. Srikanth and Y. M. Mukovskii, Journal of Applied Physics 97, 10C104 (2005)
“Probing magnetic
anisotropy and spin polarization in spintronic
materials” –P. Poddar, G. T. Woods,
“Inter-particle interactions and magnetism in manganese-zinc ferrite nanoparticles” –P. Poddar, H. Srikanth, S. A. Morrison and E. E. Carpenter, Journal of Magnetism and Magnetic Materials 288C, 443 (2005)
“Magnetism and RF dynamics in nanocomposite materials” –H. Srikanth and P. Poddar, Journal of Metastable and Noncrystalline Solids (special issue on Science and Technology of Nanomaterials, to appear in Vol. 23, p. 355, Jan. 2005)
“In-plane and out-of-plane transverse susceptibility in close-packed arrays of
monodisperse Fe nanoparticles”
– P. Poddar, J. L. Wilson, H.
Srikanth, D. F. Farrell and S. A.
Majetich
“The transverse susceptibility of uniaxial ferromagnets” –L. Spinu, A. Stancu, H. Srikanth and C. J. O’Connor, Applied Physics Letters 80, 276 (2002)
“Relaxation and interaction effects on transverse susceptibility measurements of nanoparticle systems” –L. Spinu, A. Stancu, L. D. Tung, P. Postolache, J. Fang, H. Srikanth and C. J. O’Connor, Journal of Magnetism and Magnetic Materials 242, 604 (2002)
“Magnetic studies of polymer-coated Fe nanoparticles synthesized by microwave plasma polymerization” –H. Srikanth, R. Hajndl, C. Chirinos, J. Sanders, A. Sampath and T. S. Sudarshan, Applied Physics Letters 79, 3503 (2001)