A near-monochrome collage of seven laboratory photographs cut into diagonal panels: a cryostat and vacuum chamber trailing cabling and steel flanges; an optical table with posts, a glowing lamp and a circuit board; a bright ring of light seen through a dark chamber viewport; a chamber interior with a finned copper disc, translation stages and stepper motors; a rack of long cryostat probe inserts with stacked baffles; a vacuum chamber wrapped in aluminium foil with pneumatic valves; and a chamber with a brilliant glowing plume beneath a circular electrode.

Magnon spin valve in Pt / CrPS4 / Pt

The short version

This device sandwiches a magnetic semiconductor between two platinum layers: one platinum layer injects a wave of the material's magnetism, called a magnon, and the second layer reads it out on the other side. Switching the orientation of the magnetic layer in the middle turns that signal on or off, like a valve. This is an earlier-stage, ongoing project, and this page is a short summary rather than a full write-up.

Active project, 2024 to present, in Mathias Klaeui's group at JGU Mainz.

Device and mechanism

A three-layer Pt / CrPS4 / Pt device. The bottom platinum layer excites magnons in the central CrPS4 antiferromagnetic semiconductor, both thermally (via the spin Seebeck effect) and electrically (via the spin Hall effect). The top platinum layer detects the resulting magnon signal via the inverse spin Hall effect. Valve behaviour is tuned by setting the CrPS4 antiferromagnet into different magnetic orientations under an applied field.

Three panels. Left and centre: optical micrographs of two devices, each a long narrow strip crossing between gold contact pads on a brown substrate, green in the first device and pink in the second, with several finer leads meeting the strip along its length and a dark scale bar at bottom right. Right: detected voltage in microvolts against applied magnetic field from minus 10 to plus 10 tesla at 24 K, with four curves for field angles of 0, 30, 60 and 90 degrees. All four are symmetric about zero field, dip to a minimum of about 0.4 microvolts near zero, and rise to maxima of about 1.2 to 1.5 microvolts near plus and minus 8 tesla, the 90 degree curve lying highest throughout. An inset schematic shows a slab with two electrodes on top wired to a voltmeter and a third electrode beneath wired to a current source.

Two of the devices, and the detected voltage against applied field at 24 K for four orientations of the field. The signal is symmetric about zero field and grows towards maxima near ±8 T, with the separation between the four angle curves showing that the response depends on how the field is oriented relative to the crystal.

Techniques

E-beam lithography, ion-beam etch, EDX, SEM, sputter deposition, dry-transfer stacking, optical lithography, and glove-box handling.

This project is thinly sourced. The vault holds only a terse evidence block (dates, device description, technique list) with no narrative write-up, and the only stated verification is internal Klaeui Group lab records rather than an independent source. The figure above is described from what is visible in it: what the field-angle dependence means, whether the ±8 T maxima are the valve effect itself or a background that has to be subtracted, and what the two devices differ in, are all unstated. This page needs a proper write-up pass with Aditya: what was measured, what was found, and current status, before it carries the same depth as the exchange-bias and magnetoresistance pages.